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Magnificent Meizodon

December 10, 2012, 8:54 am
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It isn't often that I'm sent a photo of a snake that I can't identify, but last week Alvaro Permartin found the time both to finish translating all of my old blog posts into Spanish (many thanks to him!) and to obtain photographs of a snake that I had never heard of before. When he sent them to me, I was struck by how beautiful and distinctive the snake was, and it turned out to be quite difficult to identify. I shouldn't have been surprised, because it is from a herpetologically-poorly-known region of the world, western Africa. Alvaro works as a doctor in Guinea, and his nurse, Sandrine Chabassieu, photographed the snake as it crawled across their porch one day.

The mystery snake
Although Kate Jackson's new key to identifying snakes of western and central Africa is a great tool, we couldn't use it to identify this snake because we didn't have close-up pictures of the all-important scale characters that can be indispensable in identifying species of snakes. The backup method, sending the photos to as many people who might know as possible, eventually proved effective when Laurent Chirio, of the Muséum National d'Histoire Naturelle in Paris, France, wrote me that "This is without any doubt a beautiful Meizodon coronatus. I found some specimens with this kind of colour pattern in Guinea."

I wanted to learn what I could about this snake, because it was so striking and previous unknown to me. There isn't a lot out there. Meizodon coronatus, also known as the Western Crowned Snake, is one of five species in Meizodon, a genus of poorly known colubrine snakes found in sub-Saharan Africa. Western Crowned Snakes are found from Senegal to the Congo along the coast of western Africa, while the other four species are found in eastern and central Africa. The Western Crowned Snake was the first species of Meizodon described, by Hermann Schlegel in 1837, who called it Calamaria coronata in his first major published work (Essai sur la Physionomie des Serpens) as assistant curator of the Natural History Museum of Leiden in the Netherlands. The species was later moved to Coronella (subgenus "Mizodon") by Giorgio Jan of the Milan Museum in 1866, then placed in Meizodon in 1955 by Arthur Loveridge.

Plate from Jan 1866

No genes of any species of Meizodon have been sequenced, so it's difficult to say exactly how they are related to other snakes, but if their placement in Colubrinae is correct, then they are probably closely related to other west African species of colubrine, such as the egg-eating Dasypeltisand wolf-toothed Lycodon. These snakes are descended from the same common ancestor as North American kingsnakes and ratsnakes, from which they diverged about 33 million years ago.

Another of Sandrine's photos

Meizodon are primarily predators of lizards, especially skinks, although they are also known to eat geckos, small mammals, and frogs. They are not as specialized for feeding on skinks as their relatives the wolf snakes (Lycodon), on which an upcoming article will focus, but their genus name describes their teeth, which increase in robustness toward the back of the jaw. Meizodon coronatus seem to be a diurnal foragers. A few individuals were observed foraging along the base of a crumbling wall by Godfrey Akani and colleagues at Rumueme, Nigeria. These snakes probed with their heads into holes and crevices where geckos and other lizards were sleeping. Typically, Meizodon are apparently found in refugia such as under rocks, within hollow trees, and underneath loose bark during the day. Don Broadley of the Zimbabwe Natural History Museum  recalls capturing several Meizodon semiornatus that were sheltering inside tree hollows in a flooded forest in western Botswana, along with the psammophine snakes Psammophylax and Psammophis. Broadley noted that several snakes were sometimes captured per tree, including evidence of shed skins and skeletons, although these observations might be atypical given the flooded nature of the forest at the time of Broadley's visit.

The best of Sandrine's photos, in my opinion, showing the gorgeous anterior pattern.

Likely viviparous, Meizodon coronatus inhabits savannahs, forests, plantations, and urban areas. They are mentioned in a study conducted by Godfrey Akani and colleagues on anthropogenic causes of snake mortality in west African suburbs. They found that anthropogenic snake mortality in suburbs of southeastern Nigeria were about 50% intentional, 50% unintentional (e.g., roadkills, snares set to trap more edible wildlife), and that more snakes were killed in the wet season, when they are presumably more active. Even though most of the snake species in this region are harmless and beneficial to humans (in that they exert strong top-down control on populations of pesty rodents, by eating them), most people did not know how to differentiate venomous from non-venomous snakes. It's interesting to know that some ecological problems are common to places as different as North America and Africa. I was glad to hear from Alvaro and Sandrine that, now that they know their beautiful snake is a harmless Meizodon, they have encouraged their camp guards not to kill other Meizodon they might see in the future.

M. coronatus from Cameroon. Not nearly as striking as the one from Guinea.
ACKNOWLEDGMENTS

Thanks to Alvaro and Sandrine for the photos, and to Pierson Hill, Peter Uetz, and Laurent Chirio for nailing the ID.

REFERENCES

Akani G, Eyo E, Odegbune E, Eniang E, Luiselli L (2002) Ecological patterns of anthropogenic mortality of suburban snakes in an African tropical region. Isr J Zool 48:1-11 <link>

Barbault R (1976) Population dynamics and reproductive patterns of three African skinks. Copeia 1976:483-490 <link>

Böhme W (2000) Diversity of a snake community in a Guinean rain forest (Reptilia, Serpentes). Bonn Zool Monogr 46:69-78

Broadley DG (1988) Meizodon semiornatus semiornatus: Semiornate Snake. Habitat, Diet, and Distribution. The Journal of the Herpetological Association of Africa 34:44

Günther A (1860) On a West-African genus of snakes (Meizodon). Proc Zool Soc Lond 28:427-430

Jan G (1866) Iconographie Générale des Ophidiens. Livraison. J.B. Bailière et Fils, Paris <link>

Luiselli L, Akani GC, Angelici FM (2001) Diet and foraging behaviour of three ecologically little-known African forest snakes: Meizodon coronatus, Dipsadoboa duchesnei and Hapsidophrys lineatus. Folia Zool 50:151-158

Schlegel H (1837) Essai sur la physionomie des serpens. Partie descriptive. Kips and Van Stockum, La Haye

Segniagbeto GH, Trape JF, David P, Ohler A, Dubois A, Glitho IA (2011) The snake fauna of Togo: systematics, distribution and biogeography, with remarks on selected taxonomic problems. Zoosystema 33:325-360
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The Unusual Soft Anatomy of Snakes

December 26, 2012, 12:57 pm
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This year I had the opportunity to help my friend Lori Neuman-Lee dissect a number of Wandering Gartersnakes (Thamnophis elegans) for her research on the effect of toxic chemicals on reptile physiology. During my Master's, I had the opportunity to help teach a Comparative Anatomy course, during which I learned a great deal about the internal anatomy of vertebrates. However, dissecting an animal for research requires greater accuracy and precision than dissecting for teaching, and we decided to read up on snake anatomy before we got started. Because we found few resources to aid us in our work, we video-taped one of the dissections to help future would-be snake anatomists locate and identify snake organs, several of which can be a little tricky. Check out the video below and learn to dissect a snake! Lori is doing the dissection in the video, and like many things, she makes it look easy. I would recommend some pretty intense practice first if you want to become as accomplished as she is. Salvaged, all-too-common road-killed specimens often make for ideal practice if you don't mind bits of them being smashed, and they sometimes have interesting things in their stomachs.


A few notes: Snakes are long - it's in the blog title. But the implications of being long for the internal anatomy of an animal are not usually considered. For example, in humans and most other animals, paired organs, such as kidneys, lungs, and gonads, are found next to one another, across the body's plane of symmetry. This is not so in snakes; there simply isn't room. Add to their body shape the fact that a great deal of the body cavity must sometimes be filled with eggs or prey items, and there's little room left for the vital organs: heart, lungs, liver, kidneys, spleen and pancreas. That's why snakes have A) evolved elongate organs, B) evolved staggered paired organs, and C) lost some organs or members of paired organs.


Many snake organs are similar in shape to their overall body form. The liver, stomach, gonads, kidneys, and lung are all elongate. Those that come in pairs are either staggered, such as the kidneys and gonads (right always anterior to left), or asymmetrical, such as the lungs. See the tiny left lung near the heart? In a real snake it's almost impossible to find. It is a vestigial organ, meaning it does not function in breathing any more, although in some sea snakes it does have a co-opted function: it helps regulate buoyancy much like the swim bladder of a fish. These adaptations are part of what makes snakes so amazing and unique.

Finally, because 2013 has been designated the Year of the Snake by non-profit conservation group Partners in Amphibian and Reptile Conservation, I hope to help them promote snake research and snake conservation through frequent writing and outreach. As always, thanks for your comments and your readership. Life is Short but Snakes are Long received over 22,000 hits in 2012 and I'm looking forward to an even bigger 2013!

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Galápagos Racers

January 16, 2013, 9:03 am
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Sadly, snakes are inactive this time of year in northern Utah. With lower-than-average temperatures dipping below 0° F every night, I've had a lot of time indoors to read and daydream about snakier times and places. You can imagine my envy of my colleagues Susannah French, Nick Kiriazis, and Lori Neuman-Lee, who are currently in the Galápagos Islands studying Marine Iguanas. Nick, a student teacher at South Cache Middle School in Hyrum, Utah, is blogging about their research experiences at his blog, The Learning Scientist, which you should check out. Before they left, I instructed them that they were not to pass up an opportunity to observe the endemic racers of the Galápagos, the only snakes to inhabit the famous archipelago (other than one sea snake species, found offshore).

Galapagos Snake from Bartholome Island
Before I began the research for this article, I was under the impression that there was only a single species of Galápagan Racer. But speciation is quick to act in the birthplace of research on evolutionary principles, and in fact there are five species, each inhabiting different groups of islands. This isn't too surprising. As with most organisms inhabiting the Galápagos (and archipelagos in general), new species evolve on different islands over a relatively short period of time. Archipelagos are natural classrooms for evolutionary biologists, each island differing slightly in a number of qualities: size, rainfall, elevation, isolation. These differing characteristics, combined with long periods of reproductive isolation from populations on other islands, result in the evolution of endemic species to each island or group of closely spaced islands. Many groups of organisms have colonized the volcanic Galápagos from South America since the islands rose from beneath the sea some 8 million years ago. In that time, many of the plants and animals have diversified and speciated, leaving behind a pattern of relationships so telling that the idea of evolution by natural selection was formulated based on observations Charles Darwin made of the islands' fauna (for a recap, follow the link above to see a video to which my friend Rosemary Mosco contributed artwork).

Galapagos Snake eating a lava lizard (Microlophus sp.)
Although one might think that Darwin probably discovered most of the species native to the Galápagos Islands, others had been there before him. The first mention of these snakes in the scientific literature came 80 years before Darwin was born, by explorer William Dampier, a natural historian whose scientific accomplishments have been largely overshadowed by his reputation as a buccaneer. In his 1729 memoir, New Voyage Round the World, he wrote "There are some Green Snakes on [the Galápagos]; but no other land-animal that I did ever see." (Although they are hardly green.) In 1839 Darwin wrote "There is one snake which is numerous; it is identical, as I am informed by [French herpetologist Gabriel] Bibron, with the Psammophis Temminckii from Chile." This turned out not to be true, and the snakes were officially described as a new species in 1860 by Albert Günther, who named it Herpetodryas biserialis, a snake "light brown with a dark brown dorsal band" and having "maxillary teeth...of moderate size,...nearly equal length,...and entirely smooth". In 1912 John Van Denburgh, Curator of the Department of Herpetology at the California Academy of Sciences, wrote a monograph on the snakes of the Galápagos as part of a report on an expedition taken by the Academy in 1905-06. In it, he gave what is still the most complete account of the snakes' (by then moved to the genus Dromicus) natural history and ecology, and described four additional species (one of which was later synonomized with an earlier description by Austrian biologist Franz Steindachner). In accordance with the prevailing geologic thinking of the day, Van Denburg suggested that the snakes, along with the other Galápagos fauna, had reached the Galápagos via a land bridge, rather than by oceanic dispersal.

Plate from Steindachner 1876
Galápagos racers mating
Today these five species are known as Pseudalsophis biserialis (which occurs in two phases, dark and light, and is found on most islands), P. dorsalis (which is striped and found on Santiago, Rábida, Baltra, Santa Cruz, and Santa Fé), P. hoodensis (which is striped and found only on Gardner and Española, formerly known as Hood Island), P. slevini (which is banded and found on Fernandina, Isabela, and Pinzón), and P. steindachneri (which is striped and found on Santiago, Rábida, Baltra, and Santa Cruz). One interpretation is that these five species comprise a clade closely related to the mainland species P. elegans, found in Ecuador and Peru and supporting Bibron's suggestion via Darwin that Galápagos racers are related to and descended from mainland snakes. Variation in pattern and scalation is present but relatively minor. Another is that there were two independent colonizations of the Galápagos by South American snakes: one by Philodryas chamissonis from Chile (this is Bibron's Psammophis temminckii) that gave rise to P. hoodensis, and the other, by P. elegans, responsible for the other species. Others have suggested that P. slevini and P. steindachneri are descended from one ancestor (possibly a species of Antillophis from the Caribbean), P. hoodensis from another (P. chamissonis), and P. biserialis and P. dorsalis from yet a third (P. elegans, which might have invaded more than once). These hypothesized dispersal pathways are similar to those suggested for Tachysphex wasps from Chile, Microlophus lizards from Peru, and shrubs of the family Nolanaceae from Peru and Chile.

A Galápagos Snake among some Marine Iguanas
To me, the first explanation seems the most parsimonious; that is, it is simplest to assume that all snakes on the Galápagos archipelago are descended from a single ancestor (P. elegans), and this is what the most up-to-date taxonomy reflects. Similarities in ecology might account for the morphological similarities that led earlier herpetologists to suggest Chilean and Caribbean ancestry. Although on some islands multiple species are found, this could be explained by multiple movements among islands of the archipelago following clonization and subsequent speciation. A 2008 review by University of Texas evolutionary biologist Christine Parent and her colleagues found that most of the Galápagos terrestrial fauna with known phylogenies (family trees), such as tortoises and finches, have diversified in parallel with the geological formation of the islands, supporting the idea that they colonized the islands only once. Because no detailed molecular phylogeny is available for Galápagos snakes, the final answer to the question of their origin and relationships has not yet been revealed.


Galápagos snake eating a small iguana
I was surprised to find how poorly known these snakes were given the infamy of the islands they inhabit. Because they are probably important predators on Galápagos finches, mockingbirds, and small lizards, as well as on non-native rodents, they deserve more study (although as Nick has pointed out, permission to study animals in the Galápagos can be difficult to obtain). Along with many of the Galápagos' other reptiles and birds, the snakes were probably almost driven to extinction by introduced cats and rats, against which they had not evolved defensive behaviors. Their natural predators probably include Galápagos mockingbirds. Today, tourism and development, although limited in the Galápagos, probably threatens these snakes as much as invasive species, which are beginning to be brought under control. Nick, Lori, and Susannah are busy studying the effects of tourism on the Marine Iguanas - who is studying the Galápagos snakes?

Even in the Galápagos, snakes are not immune to vehicular manslaughter

ACKNOWLEDGMENTS


Special thanks to Nick Kiriazis for inspiring me to write this article with his blog, and thanks to Lori Neuman-Lee, Manuel Mejia, Dave Irving, Jim Moulton, Rosalind Gomes, and Phillip Marsh for their pictures.

REFERENCES

Grehan J (2001) Biogeography and evolution of the Galápagos: integration of the biological and geological evidence. Biol J Linn Soc 74:267-287 <link>

Günther A (1860) On a new snake from the Galápagos islands. The Annals and Magazine of Natural History 3:78-79

Parent CE, Caccone A, Petren K, 2008. Colonization and diversification of Galápagos terrestrial fauna: a phylogenetic and biogeographical synthesis. Philosophical Transactions of the Royal Society B: Biological Sciences 363:3347-3361 <link>

Steindachner F (1876) Die schlangen und eidechsen der Galapagos-inseln. Zoologisch-botanischen Gesellschaft, Wien, Germany. <link>

Thomas R, 1997. Galápagos terrestrial snakes: biogeography and systematics. Herpetol Nat Hist 5:19-40.

Van Denburgh J (1912) Expedition of the California Academy of Sciences to the Galapagos Islands, 1905-1906. IV. The snakes of the Galapagos Islands. Proceedings of the California Academy of Sciences (Series 4) 1:323-374

Zaher H, Grazziotin FG, Cadle JE, Murphy RW, Moura-Leite JC, Bonatto SL, 2009. Molecular phylogeny of advanced snakes (Serpentes, Caenophidia) with an emphasis on South American Xenodontines: A revised classification and descriptions of new taxa. Pap Avulsos Zool (Sao Paulo) 49:115-153 <link>
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Africa's Giant Gaboon Vipers

January 29, 2013, 6:57 am
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For as long as I can remember, I've been impressed by Gaboon Vipers (Bitis gabonica). These western African behemoths can reach 5 3/4 feet in length and over 14.5 inches in girth, and weigh up to 25 pounds with an empty stomach. They are the heaviest vipers and possess the longest fangs, up to one and a half inches in length! Furthermore, their geometric dorsal pattern, as intricate as it is beautiful, is ideally suited to camouflaging them against the leafy forest floor, where they lie in wait for their endothermic prey: birds, rodents, rabbits, monkeys, small antelope, porcupines.

A Gaboon Viper, beautifully camouflaged
Like many vipers, Gaboon Vipers are ambush predators, a lifestyle to which they are supremely adapted. Long folding fangs and deadly venom allow them to kill their prey while keeping a safe distance from it. A very low metabolism permits them to wait in one spot for weeks, until the perfect opportunity presents itself. They spend between three-quarters and 95% of their time just sitting quietly, sometimes for up to three months at a time. Every so often, a viper, particularly a male during the breeding season of March through May, will embark on a long-distance movement of one quarter to two thirds of a mile, sometimes in a single day.1 The preferred habitat of Gaboon Vipers is a mosaic of forest, thicket, and grassland, although they will sometimes enter sugarcane fields and rural gardens. As with most snakes, life as a Gaboon Viper is probably pretty dull.

The impressive fangs of a Gaboon Viper
In spite of its impressive size, or perhaps because of it, Gaboon Vipers are, like many of their kin, docile and retiring. "On two occasions, I accidentally stepped directly on B. gabonica during the course of radiotracking, only becoming aware of this after feeling squirming movement beneath my foot. At no point during either encounter did the snake hiss or show aggression in any manner", writes Jonathan Warner in his dissertation, which also contains evidence that hippos, elephants, and leopards may walk right by Gaboon Vipers without noticing them. Being stepped on and squashed by these large herbivores might be the primary cause of mortality for adult vipers, which are not vulnerable to many natural predators.

You can see why
Although Gaboon Vipers produce prodigious amounts of venom (nearly 10 mL), the toxicity is rather low compared to other venomous snakes, and there are only a few detailed clinical reports of bites. They are undoubtedly dangerous snakes, but envenomations are few compared to such infamous species as the Russell's Viper. Like most snakes, particularly slow-moving ones with good camouflage, Gaboon Vipers usually sit still and remain unnoticed whenever a human comes nearby (so in other words, pretty much the exact same thing they were already doing).

Gaboon Viper plate from Duméril, Bibron, & Duméril's Erpétologie Générale;
unfortunately, this is one of the only plates not in color
Like most vipers, female Gaboon Vipers give birth to a litter of live young once every two to three years, usually between 20 and 40. Females do not eat while pregnant. Little is known about their reproductive behavior, but males combat one another over females, which must be an impressive sight. Much recent research on Gaboon Vipers has taken place in South Africa, where they are known as Gaboon Adders. In the southernmost populations, which are disjunct from the main range of the species, the climate is subtropical and seasonal differences in activity are observed, but radiotelemetry studies conducted in tropical areas of Cameroon and Nigeria show no seasonal changes in behavior.2

East African Gaboon Viper (B. g. gabonica)
What's the thing on their nose for? It is much larger in the West African subspecies than in the East African one. Hypotheses range from enhancing crypsis to doing nothing at all. Darren Naish at Tetrapod Zoology has addressed this question, but it seems he met with about the same amount of success as I did in finding a compelling, well-supported reason why these snakes have horns. I couldn't find any studies that examined whether the horns had a sensory function, although it certainly seems possible.


West African Gaboon Viper (B. g. rhinoceros)
I learned something new about these vipers recently. It seems that, among other heavy-bodied snakes, they have evolved the ability to retain their feces for incredibly long periods of time - months to years, after which time 5-20% of the body weight of a single snake may be feces. While this would kill a human, retained fecal material may be functioning as metabolically inert ballast in these species, which require a stationary inertial base for striking. Available data suggest that enhanced uptake of water and nutrients can also be achieved in snakes retaining feces - the poisonous urates (read: pee) are excreted more frequently. Amazing.

1  One exception is that these snakes always move following shedding, which occurs about twice a year, perhaps to distance themselves from potential predators attracted by the sloughed material or to avoid external parasites in the old skin that could reattach to the snake.↩
2 Snake biologists in Africa face challenges unfamiliar to we North Americans: "In several instances, I had to abort tracking efforts due to B. gabonica locations in close proximity to potentially dangerous game; namely [Water Buffalo, Rhinoceros, Elephant, Hippopotamus, and Crocodile]", writes Jonathan Warner in his dissertation.↩


ACKNOWLEDGMENTS

Thanks to Tim Vickers, Wolfgang Wuster, Ivica, Markus Oulehla, and Jonathan Warner for their photos.

REFERENCES

Lillywhite HB, de Delva P, Noonan BP (2002) Patterns of gut passage time and chronic retention of fecal mass in viperid snakes. In: Schuett GW, Höggren M, Douglas ME, Greene HW (eds) Biology of the Vipers. Eagle Mountain Publishers, Eagle Mountain, UT, pp 497-506

Linn I, Perrin M, Bodbijl T (2006) Movements and home range of the gaboon adder, Bitis gabonica gabonica, in Zululand, South Africa. Afr Zool 41:252-265

Luiselli L (2006) Site occupancy and density of sympatric Gaboon viper (Bitis gabonica) and nose-horned viper (Bitis nasicornis). J Trop Ecol 22:555-564

Marsh NA, Whaler BC (1984) The Gaboon Viper (Bitis gabonica): Its biology, venom components and toxinology. Toxicon 22:669-694

Warner JK (2009) Conservation Biology of the Gaboon Adder (Bitis gabonica) in South Africa. PhD dissertation, School of Animal, Plant, and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.
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Malagasy Leaf-nosed Snakes

February 7, 2013, 9:33 am
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Langaha madagascarensis male
Madagascar has been called the "eighth continent" as a result of its large size, unique habitats, and high faunal and floral (not to mention cultural and linguistic) endemism. Of the ninety-six species of snakes inhabiting the island, only two are found anywhere else: one is a sea snake (the widespread Pelamis platura) and the other is a ubiquitous introduced species (the parthenogenetic blindsnake Ramphotyphlops braminus). Most of the rest belong to the subfamily Pseudoxyrhophiinae, and each deserves its own article. But one has to start somewhere, and perhaps the best place to start is with one of the most unique Malagasy snakes, and one of my favorites: Langaha madagascarensis, the Malagasy Leaf-nosed Snake.

Langaha madagascarensis female
Langaha is so unique that it has been placed in its own genus ever since it was described, and was one of only eight1 genera recognized in Bonnaterre's 1790 Ophiologie, a book that covered 224 species of snake. That's right: at a time when snakes as different as wormsnakes, saw-scaled vipers, sea snakes, and blunt-headed tree snakes were being grouped together as "typical snakes" in the genus Coluber, Langaha was considered unusual enough to justify its own genus! Today there are three recognized species of Langaha, but the most is known about L. madagascarensis.

Left: Captive juvenile Langaha madagascarensis exhibiting hanging behavior; photo from Krysko 2003
Right: Seed pods of the Ophiocolea floribunda, a Malagasy legume whose genus is Greek for 'hollow snake'
As their name implies, Leaf-nosed Snakes have bizarre nasal appendages. What's more, these structures are sexually dimorphic to a degree unusual among snakes. Female Leaf-nosed Snakes have a more elaborate, serrated nasal appendage, whereas males bear a longer, pointier one. These structures are present at birth, suggesting that they have some function beyond sexual signaling between rival males or potential mates. Often, these snakes are seen hanging from branches with their heads pointing towards the ground - perhaps the structures serve to drain water off the snake? Several Malagasy plants, including some legumes and bignonias, have long pointed seed pods that hang down from the plant, providing possible models that the snake may imitate with its posture and nasal appendage. No one knows for certain.

Male (right) and female
(left) L. madagascarensis 
This is a timely post in that it comes on the heels of newly published research on Malagasy Leaf-nosed Snakes. An article by recent Cornell University graduate Jessica Tingle has just appeared in the journal Herpetological Conservation and Biology documenting novel aspects of the behavioral ecology of this unusual snake. Everything known about the behavior of Langaha to date has been learned from observing captive individuals. Tingle's paper presents the first data collected on the behavior of Langaha in the wild. She observed several of these snakes foraging for and eating lizards, although one sentence in her paper stands out to me as typical of snake behavior studies: "The vast majority of their time (90%) was spent not moving at all." Although this sounds boring, it provides evidence that these snakes are primarily ambush predators, rather than active foragers (although Tingle did observe one Langaha chasing skinks on the ground). Spending months in Madagascar, Tingle was able to observe only a few snakes, and much remains to be learned about their natural history and ecology.

Plate showing a male Langaha madagascarensis from Bonnaterre's 1790 Ophiologie
From observations made on Langaha in captivity by Kenney Krysko of the Florida Museum of Natural Sciences, we know that Leaf-nosed Snakes lay eggs. When they hatch, the nasal appendages of juveniles are folded up so that their egg tooth can be used to break out of the egg. The appendage gains its normal shape after 36 hours. Juveniles exhibit the same vertical 'hanging' behavior as adults, which Krysko also suggests helps them mimic the seed pods of Malagasy plants (and perhaps deter predation, though by what predator is unclear).

Hatchling Langaha madagascarensis, from Krysko 2003
The other two species of Langaha are very poorly known. In Darren's TetZoo article, he states that only female Langaha alluaudi have nasal appendages, but I have been unable to find another source corroborating this fact, although I did find a photo on Flickr purported to be a male L. alluaudi (it looks similar to a male L. madagascarensis, also sometimes called L. nasuta, to me). Female L. alluaudi have longer, straighter nasal appendages than L. madagascarensis, and female L. pseudoalluaudi have shorter, more upturned ones (no word on what male L. pseudoalluaudi might look like). Why these differences? Perhaps differences in microhabitat or sexual preference are the cause. Who can say?

Female (left) and male(?, right) Langaha alluaudi

Female L. pseudoalluaudi

Although Madagascar is unique, it is similar to the rest of the world in at least one sad way: its natural places are disappearing quickly. Most of its forests have already been logged or converted to slash and burn agriculture, and what little remains is dwindling daily. If more effective conservation measures are not taken,  including supporting the human communities that depend on the rich natural resources of this hottest of biodiversity hotspots, we may never find out what Langaha's nose is for.

Male L. madagascarensis consuming Chalarodon madagascariensis
Photo from Herp. Con. Bio. gallery for Tingle 2012

1 Three of these eight genera turned out not to be snakes at all: the limbless lizards Anguis and Amphisbaena, and  the limbless amphibian Caecilia.↩

ACKNOWLEDGMENTS

Thanks to Dick Bartlett, Jessica Tingle, David d'O, Bernard Dupont, Russell Speight, and G.E. Schatz for use of their photos.

REFERENCES

Bonnaterre PJ (1790) Ophiologie, in Tableau encyclopédique et méthodique des trois règnes de la nature. Panconoke, Paris <link>

Krysko KL (2003) Reproduction in the Madagascar leaf-nosed snake, Langaha madagascariensis (Serpentes: Colubridae: Pseudoxyrhophiinae). African Journal of Herpetology 52:61-68 <link>

Krysko KL (2005) Feeding behaviour of the Madagascar leaf-nosed snake, Langaha madagascariensis (Serpentes: Colubridae: Pseudoxyrhophiinae), with an alternative hypothesis for its bizarre head structure. African Journal of Herpetology 54:195-200 <link>

Tingle JL (2012) Field observations on the behavioral ecology of the Madagascan Leaf-nosed Snake, Langaha madagascariensis. Herpetological Conservation and Biology 7:442-448 <link>
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Screech Owls and Blindsnakes: An Unlikely Mutualism

February 28, 2013, 7:13 am
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Adult Eastern Screech Owl at a nest box
In the 1970s and 80s, a pair of biologists at Baylor University in Waco, Texas, Fred Gehlbach and Robert Baldridge, were studying screech owl nesting ecology. These small owls nest in tree cavities and eat a variety of small animals, from insects to mice. Like most raptorial birds, Eastern Screech Owls usually kill their prey before bringing it home to feed to their nestlings. Gehlbach and Baldridge observed some of the screech owls in their study carrying live Texas Blindsnakes (Rena [formerly Leptotyphlops] dulcis) to their nests in experimental nest boxes like those used by wood ducks and bluebirds (pictured at right). When they checked the nests the next day, they found, to their surprise, between one and fifteen live blindsnakes living among the owl chicks in fourteen different nests! In some cases, the snakes lived with the baby owls for at least a week! Many of the blindsnakes bore scars from adult owl beaks, but few had been killed.

If you're not familiar with blindsnakes (aka scolecophidians), don't worry; few people are. There are about 400 species of these 'seriously strange serpents', as Darren Naish calls them over at TetZoo, distributed chiefly in the world's tropical regions (the Texas Blindsnake is one of the few temperate exceptions). Most have small eyes (or none at all, as their name suggests), smooth round scales, and eat invertebrates. Their jaw architecture is entirely unique: their jaws act like little scoops to effectively shovel ant and termite larvae and pupae into their mouths. Check out the video from BBC's Life in Cold Blood below, or visit the homepage of blindsnake biologist Nate Kley at Stony Brook University.


Almost as cute as baby snakes
How does this help baby screech owls? Gehlbach and Baldridge wanted to find out, so they measured the diversity and abundance of invertebrates in the owl nests with and without live blindsnakes, as well as the health and survival of the baby owls (which they were already measuring). They found that nests with blindsnakes had significantly fewer mites, insects, and arachnids, and that baby owls from these nests were 25% more likely to survive and grew as much as 50% faster; in other words, the presence of the blindsnakes improved the health of the baby owls and the fitness of the adults. The effects were more pronounced for the youngest owl babies, which hatch as many as six days later than their oldest sibling. As the nail in the coffin, Gehlbach and Baldridge tested whether or not the blindsnakes actually ate the invertebrates they found in the owl nests, and sure enough, they chowed down on the soft-bodied fly larvae that kill baby owls in nearly 30% of nests.

Texas Blindsnake (Rena dulcis)
They also noticed that blindsnakes were more likely to be found in nests after it rained, probably because the mother owls had an easier time of finding the blindsnakes when they were crawling around on the surface, which many fossorial snakes tend to do when rainwater fills their burrows. Gehlbach and Baldridge also found that blindsnakes could only survive about two weeks in owl nest boxes that did not contain baby owls, suggesting that they were dependent on insect larvae that entered the nest inside food brought by the mother owl. These snakes can climb trees, so presumably it isn't too challenging for them to climb down out of a nest box after it is vacated by owls; one gravid female blindsnake was found in a nest box, so it is possible that they lay their eggs there before leaving. Some nests contained dead blindsnakes, which Gehlbach and Baldridge hypothesized had been eaten by the baby owls after their food supply had run out. In feeding experiments, baby screech owls readily consumed dead blindsnakes as well as other snakes of similar size, such as Rough Earthsnakes (Virginia striatula).

Skull architecture of Rena dulcis
The skulls of blindsnakes are just amazing, and it's thanks to the research efforts of blindsnake anatomist Nate Kley of Stony Brook University that we know so much about them. Kley has characterized the feeding behavior of two families of blindsnakes, the Leptotyphlopidae, which use  scooping motions of the lower jaw known as mandibular raking, and the Typhlopidae, which use similar motions of the upper jaws, called maxillary raking. It's remarkable how similar the two strategies are given that the snakes are using entirely different parts of their bodies to employ them and that they are separated by about 110 million years of evolution. High-resolution CT scans of the skill of Rena dulcis are also available from the good people at UT Austin's DigiMorph project. The jaws (upper in typhlopids, lower in leptotyphlopids) move about independently of the skull to a remarkable degree. You can get a really good idea of that motion by watching videos of leptotyphlopids here, here, and here, and of typhlopids here and here. As soon as they're in the mouth, those larvae are goners! These snakes are unlike all others in that they eat  huge numbers of prey items very quickly, thanks to their unique jaw architecture. One Blackish Blindsnake (Austrotyphlops nigrescens) from Australia was recorded to have eaten over 1,431 ant larvae/pupae in one sitting! Some blindsnakes have cloacal secretions that aid in repelling attacking ants or chemically camouflaging the blindsnakes, which live inside ant mounds. The list of amazing attributes goes on and on - and there is much more for scientists to find out!

ACKNOWLEDGMENTS

Thanks to Count_Strad, Toby Hibbits, Gary Nafis, and Nate Kley for use of their photos and figures.

REFERENCES

Gehlbach, F. and R. Baldridge. 1987. Live blind snakes (Leptotyphlops dulcis) in eastern screech owl (Otus asio) nests: a novel commensalism. Oecologia 71:560-563. <link>

Kley, N. J. 2001. Prey transport mechanisms in blindsnakes and the evolution of unilateral feeding systems in snakes. American Zoologist 41:1321-1337. <link>
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Non-toxic venoms?

March 19, 2013, 7:52 am
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This article is part of a series highlighting new research in snake biology presented by herpetologists at the World Congress of Herpetology VII in Vancouver, British Columbia. If you want to learn more about the WCH, check out the June 2012 issue of Herpetological Review, or follow the Twitter hashtag #wch2012, with which I will tag all posts in this series.

A while back we heard about reasons why rattlesnakes frequently miss strikes at their squirrel prey. When they do hit their target, however, the prey tend to run off a little ways before kicking the bucket. This is because, although snake venoms are quick-acting, they mostly do not incapacitate immediately (although there are some sea snake venoms that are very, very quick). As a result, snakes that hunt using venom must be able to track down their prey after it has been bitten. This necessity has led Anthony Saviola, Steve Mackessy, and their colleagues at the University of Northern Colorado to an answer for a question that snake biologists have been asking for a long time: why do snake venoms contain molecules that are non-toxic?

Venom is a complex mixture of over one hundred proteins, peptides, enzymes, and small organic and inorganic molecules, many of which are toxic. It is essentially very strong saliva, capable of both breaking down food and chemically incapacitating or killing it. The evolution of venom has allowed many species of advanced snakes to utilize chemical rather than mechanical means of dispatching prey, which helps them avoid retaliation from sharp teeth and claws. Yet a few venom components serve neither to digest nor to kill prey. What on earth is their function?

Timber Rattlesnake, Crotalus horridus
Observations back to the 1960s suggest that rattlesnakes prefer the scent of envenomated mice over non-envenomated ones. When a rattlesnake strikes a prey item, a stereotypic behavior known as strike-induced chemosensory searching (SICS) is induced. This behavior is a fixed-action pattern that involves tongue-flicking to collect chemical information and a stereotyped searching movement pattern that allows the snake to determine which of the many chemical trails in its vicinity should be followed to find the envenomated prey.

To what chemical cues are rattlesnakes responding when they perform SICS? Mackessy separated Western Diamondback Rattlesnake (Crotalus atrox) venom into distinct fractions, each containing molecules of different sizes. This is accomplished by exploiting differences in the weight of each molecule, using techniques that allow different molecules to travel different distances through a gel medium based on how heavy they are. In the same amount of time, smaller, lighter molecules travel farther than larger, heavier ones. When Mackessy injected mice with the fractions containing the larger exonucleases, metalloproteinases, and phospholipases (classes of enzymes that break down, respectively, DNA, proteins, and fatty acids - so, the venom components that are active in digestion and incapacitation), the snakes showed little interest. Together, these well-known active compounds comprise about 85% of the total venom by mass, and they are responsible for all of the venom's digestive and killing activity, so it's a little surprising that snakes should show no interest in mice injected with them.

Structure of disintegrin heterodimer from Echis carinatus
However, when Mackessy injected mice with a venom fraction containing smaller molecules, called crotatroxin disintegrins, not known to have any enzymatic or toxic activity, the snakes behaved as they normally would have when scent-trailing mice injected with whole venom. Although disintegrins make up less than 10% of the venom by mass, they are clearly critical for the snake to find its prey following envenomation. What's more, the disintegrins alone don't induce trail-following behavior in snakes; rather, it is the product of the interaction of the disintegrins with the dead prey tissue that causes snakes to follow their trail.

Crotalus oreganus lutosus
Disintegrins are abundant in the venoms of most Western Rattlesnakes (Crotalus viridis sensu lato)1, and are also found in other rattlesnakes, in Copperheads (Agkistrodon contortrix) and other snakes of the genus Agkistrodon (where they may be undergoing rapid evolution), and in most adult vipers. However, in juvenile rattlesnakes, and in many elapid snakes (cobras, coralsnakes, and other proteroglyphous snakes) disintegrins are present only at low levels or are absent entirely. Why should this be? One possible explanation is that elapids and juvenile vipers are more likely to hold onto their prey following a strike, so they don't need a chemical tracer to follow it because it doesn't usually get that far away. Some elapids do have disintegrins, however, and there is evidence that disintegrins in vipers also function to inhibit blood coagulation. In fact, a disintegrin molecule from Copperhead venom has been shown to slow the spread of breast and ovarian cancer in mice, so there could be much more to this story. One thing is sure: the Mackessy lab is one to watch if you're interested in snake venoms, and this won't be my last post on their fascinating research.
1 Many of the nine previously recognized subspecies of the Western Rattlesnake (Crotalus viridis sensu lato) occur in the southwestern United States, and the complex has been subject to several molecular studies to reevaluate the taxonomic status of these subspecies. The consensus opinion largely follows Ashton and de Queiroz (2001), which recognized two species: C. viridis (Prairie Rattlesnake, two subspecies) and C. oreganus (Western Rattlesnake, six subspecies). This is the only species of rattlesnake that occurs where I live, in northeastern Utah.↩

ACKNOWLEDGMENTS

Thanks to Todd Pierson for his photograph and to Steve Mackessy and Anthony Saviola for their coordination on this article, which was delayed in its release to coincide with the publication of their paper in BMC Biology.

REFERENCES

Ashton KG, de Queiroz A (2001) Molecular systematics of the western rattlesnake, Crotalus viridis (Viperidae), with comments on the utility of the D-loop in phylogenetic studies of snakes. Molecular Phylogenetics and Evolution 21:176-189. <link>

Calvete J, Sanz L, Juárez P, Mackessy S (2009) Snake venomics and disintegrins: portrait and evolution of a family of snake venom integrin antagonists. In: Mackessy S (ed) Handbook of Venoms and Toxins of Reptiles. CRC Press, Boca Raton, Florida, pp 337-357

Finn R (2001). Snake Venom Protein Paralyzes Cancer Cells. Journal of the National Cancer Institute 93:261-262 <link>

Furry K, Swain T, Chiszar D (1991) Strike-induced chemosensory searching and trail following by prairie rattlesnakes (Crotalus viridis) preying upon deer mice (Peromyscus maniculatus): chemical discrimination among individual mice. Herpetologica 47:69-78. <link>

Mackessy SP, Tu AT (1993) Biology of the sea snakes and biochemistry of their venoms. In: Tu AT (ed) Toxin-related Diseases: Poisons Originating from Plants, Animals and Spoilage. Oxford & IBH Publishing Co., New Delhi, pp 305-351 
<link>

Saviola AJ, Chiszar D, Busch C, Mackessy SP. 2013. Molecular basis for prey relocation in viperid snakes. BMC Biology 11 <link>

Soto JG et al. (2006) Genetic variation of a disintegrin gene found in the American copperhead snake (Agkistrodon contortrix). Gene 373:1-7. <link>
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Fea's Viper

April 10, 2013, 8:30 am
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Leonardo Fea
Late one spring night in 1887 in the Kakhyen Hills of Burma, 35-year-old Italian explorer Leonardo Fea crested a karst outcrop and entered a bamboo thicket. He barely noticed the rain, because before him lay a two-foot long snake of indescribable beauty. It was shiny, dark purplish-black and marked with thin, widely-spaced neon orange bands so bright they almost  looked white. The head bore a striking symmetrical pattern of orange, gold, and black. When Fea picked the snake up, he saw that it had a plain purple belly. It appeared to be a harmless colubrid, and luckily for Fea, he wasn't bitten, so he had no opportunity to find out that it wasn't.

Fea was among the many European explorers and natural historians who were pouring into the newly-annexed nation of Burma, whose cultural roots date back to the 2nd century BCE. He collected thousands of vertebrates there for the Genoa Civic Museum, but perhaps none so unique or amazing as that snake. When Belgian-British herpetologist George Boulenger received a loan of Fea's reptiles from the museum, he declared of the single specimen "I may well say that Azemiops is the most interesting ophiological discovery made since that of Dinodipsas [Causus]1". Boulenger described it as a new genus and species in his 1888 report on Fea's expedition, writing "it affords me great pleasure to connect with [this snake] the name of the courageous and highly successful explorer to whom science is indebted for this and so many other additions." Azemiops feae was the first species named for Fea, who was soon to also receive the honors of an eponymous petrel, tree rat, and muntjac, collected with his "untiring zeal" in southeast Asia and the Cape Verde islands.

Azemiops feae. Notice the enlarged head scales
and the absence of a heat-sensing facial pit.
The enigmatic “pitless pitviper,” Azemiops feae or Fea's Viper looks almost nothing like other vipers, with its elliptical head, enlarged head scales, and smooth dorsal scales. In fact, it is so unusual that at times it has been classified as an elapid or a colubrid instead, of which its enlarged head scales in particular are reminiscent. Morphological and molecular evidence point to an ancient relationship between Fea's viper and other old world vipers ("viperines"), which last shared a common ancestor over 56 million years ago. Rather, Fea's viper is more closely related to the crotaline vipers, or "pit vipers", a predominantly New World clade that includes rattlesnakes, copperheads, and bushmasters (although even from these it is distinct, having diverged over 32 million years ago). Although there are a few other Asian crotalines, such as Hypnale and Trimeresurus, even these are more closely related to their New World counterparts than they are to Fea's viper, all sharing an infrared-sensitive facial pit. Indeed, Azemiops occupies a lonely branch of the snake family tree.

We know a little of the natural history of Fea's viper. It is found primarily in karst systems in the tropical uplands of northern Burma, northern Vietnam, and south-central China. Adults are active predominantly during cool, rainy summer nights, when they move slowly through deep leaf-litter in bamboo and tree fern thickets interspersed with well-lit clearings. They spend much of their lives in the holes and crevices of karst outcrops and in open and underground streams. Juveniles are most active on cool, wet fall nights. Like other vipers, Fea's viper hibernates in winter, so presumably they are fairly predictable in space and time when entering and leaving their hibernacula. Only a few prey items have been recorded, all of which have been rodents and shrews abundant in karst outcrops associated with swift mountain streams, although these snakes will also eat geckos in captivity.

This specimen's head shows more than the usual amount
of white. In preservative, the head turns completely white,
causing some to call them "White-headed Vipers".
Fea's vipers are rare and difficult to keep in captivity. In 1986, the price list for Scales & Tails Trading Company in Hong Kong offered five Azemiops feae as "White Head Vipers" for $300 a piece, the most expensive item on the list. Observations of captive individuals indicate that these snakes do not tolerate dry conditions, and develop skin problems when maintained at less than 100% humidity. Ideal temperatures are between 60 and 68°F, surprisingly cool for a reptile (but a little warmer than those preferred by Rubber Boas). In the words of one reptile keeper, they are "so boring & difficult to keep" that he sent his off to a zoo. If widely held, this sentiment may actually bode well for Fea's vipers if it renders them unlikely to become overcollected for the pet trade, especially if the low demand can be met by captive breeding. Mating behavior involves courtship of females by males and is similar to that of other vipers in most respects. Fea's vipers lay small clutches of eggs, a characteristic they share with most viperines but not their closer relatives, the crotalines.

Plate from Boulenger's 1888 Account of the Reptilia obtained in Burma,
north of Tenasserim, by M. L. Fea, of the Genova Civic Museum
Skull of a Fea's Viper, showing the solenoglyphous fang,
the definitive viper characteristic.
How dangerous are Fea's vipers? Few bites have been reported, but these are described as "mild", causing few serious consequences. There are similarities between Fea's viper venom and that of viperines, especially Wagler's Temple Viper, except that Azemiops venom has no blood clotting, hemorrhagic, or muscle-destroying activity. The venom gland itself is similar to a viperine's, but Fea's viper fangs possess a ridge at the tip and a blade on the back seen only in some opisthoglyphous and atractaspid snakes. One venom component, dubbed azemiopsin, has been identified as a potential model in neurotransmitter research, adding to the pharmacopoeia of medicinally-useful compounds found in snake venom. Although discovered 125 years ago, Fea's viper has much still to teach us about evolution, neurology, and much else. Let us hope we can learn from it.

1 The genus Caususconsists of six species of viper from sub-Saharan Africa commonly known as night adders. Night adders were once considered the most primitive vipers due to their round pupils and enlarged head scales, which is why Boulenger found them remarkable. They are oviparous and are now known to be more closely related to viperines than to Azemiops and crotaline vipers. Look out for an article on them up here one day!↩


ACKNOWLEDGMENTS

Thanks to Gernot Vogel, David Nixon, and Michael and Patricia Fogden for use of their photographs.

REFERENCES

Andreone, F. 2000. Herpetological observations on Cape Verde: a tribute to the Italian naturalist Leonardo Fea, with complimentary notes on Macroscincus coctei (Duméril & Bibron, 1839) (Squamata: Scincidae). Herpetozoa 13:15-26

Boulenger, G. A. 1888. An account of the Reptilia obtained in Burma, north of Tenasserim, by M. L. Fea, of the Genova Civic Museum. Annali del museo civico di storia naturale di Genova, Seria 2 6:593-604

Kardong, K. V. 1986. Observations on live Azemiops feae, Fea's Viper. Herpetological Review 17:81-82

Liem, K., H. Marx, and G. B. Rabb. 1971. The viperid snake Azemiops: its comparative cephalic anatomy and phylogenetic position in relation to Viperinae and Crotalinae. Fieldiana: Zoology 34:189-196

Mebs, D., U. Kuch, and J. Meier. 1994. Studies on venom and venom apparatus of Fea's viper Azemiops feae. Toxicon 32:1275-1278 <link>

Orlov N, Ananjeva N, Khalikov R (2002) Natural history of pitvipers in eastern and southeastern Asia. In: Schuett GW, Höggren M, Douglas ME, Greene HW (eds) Biology of the Vipers. Eagle Mountain Publishers, Eagle Mountain, UT, pp 345-360 <link>

Utkin, Y. N., C. Weise, I. E. Kasheverov, T. V. Andreeva, E. V. Kryukova, M. N. Zhmak, V. G. Starkov, N. A. Hoang, D. Bertrand, J. Ramerstorfer, W. Sieghart, A. J. Thompson, S. C. R. Lummis, and V. I. Tsetlin. 2012. Azemiopsin from Azemiops feae viper venom, a novel polypeptide ligand of nicotinic acetylcholine receptor. Journal of Biological Chemistry 287:27079-27086 <link>

Wüster, W., L. Peppin, C. Pook, and D. Walker. 2008. A nesting of vipers: Phylogeny and historical biogeography of the Viperidae (Squamata: Serpentes). Molecular Phylogenetics and Evolution 49:445-459 <link>

Zhao, E.-M. and G. Zhao. 1981. Notes on Fea's Viper (Azemiops feae Boulenger) from China. Acta Herpetologica Sinica 5:66-71
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Spider-tailed Adders

April 30, 2013, 6:27 am
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This species was brought to my attention about two years ago by a friend who, like me, was working on completing her Master's thesis at that time. In the post-script of her message, titled 'Probably the coolest thing I've learned in weeks', she wrote "PS I swear this started out as a legitimate search for information for my thesis." In addition to being a welcome distraction from my writing, the story of the Spider-tailed Horned Viper, Pseudocerastes urarachnoides, is, in my opinion, one of the most interesting recent discoveries in herpetology.

The tail in question
The first specimen of P. urarachnoides was collected in 1968 by the Second Street Expedition, mounted on behalf of Chicago's Field Museum of Natural History by a retired businessman and activist couple, William and Janice Street. The primary purpose of the expedition was to collect mammal specimens, but reptiles were also collected, including the first specimen (also known as a type specimen or holotype) of P. urarachnoides. Because only a single specimen was collected, its unusual tail morphology was thought at first to be a solfugid clinging to the tail. Solfugids (also called solpugids, camel spiders, wind scorpions, or sun spiders) are members of the same arthropod class, the Arachnida, as spiders and scorpions, although they are neither spiders nor scorpions. Upon closer examination, the Field Museum's Steven Anderson found that the tail of the snake bore a peculiar structure with an uncanny resemblance to a solfugid that could have been a tumor, congenital defect, or growth caused by a parasite. The snake was identified as Pseudocerastes persicus, the Persian Horned Viper, and entered into the Field Museum collection, where it was almost, but not quite, forgotten.

Egyptian Giant Solfugid (Galeodes arabs)
The story ended there, until 2001, when Hamid Bostanchi collected a second specimen with identical tail morphology to the first. A third specimen was later discovered in the collection of the Poisonous Animal Section of the Razi Institute in Karaj, Iran, in 2008; it had been misidentified as a Desert Horned Viper, Cerastes cerastes. Together with Anderson, who had described the first specimen, and their colleagues Haji Gholi Kami of Gorgan University and Ted Papenfuss of the Berkeley Museum of Vertebrate Zoology, they described the new species in 2006, naming it Pseudocerastes urarachnoides, from the Greek ura (tail), arachno (spider) and ides (similar to). In their paper, Bostanchi et al. described the structure of the tail, which is formed of the last pair of subcaudal scales, much enlarged, and a single enlarged dorsal scale. The elongated components are modified lateral scales. X-rays taken by the team showed that the caudal vertebrae extend well into this structure and are not deformed or modified. Bostanchi et al. also speculated that the function of the modified tail might be to augment caudal luring behavior exhibited by many vipers. By mimicking a solfugid, birds or other would-be solfugid predators could be enticed to approach within the viper's striking distance.

Behavioral observations made in 2008 of a live P. urarachnoides captured in western Iran and maintained in captivity confirm these ideas. Closed-circuit video was used to record behavior, and the results published in the Russian Journal of Herpetology by Behzad Fathinia of Razi University and his colleagues. They observed the snake, a juvenile male that regurgitated a Crested Lark, using its caudal lure to attract sparrows and baby chickens that they introduced into its enclosure. When the birds approached and pecked the tail, the snake struck and envenomated the birds, a process taking less than one half second. A bird was also found in the stomach of the paratype specimen, further evidence that this species might feed heavily on birds in the wild with the aid of its spectacular caudal lure. The tail of P. urarachnoides probably represents the most elaborate morphological caudal ornamentation known in any snake, with the possible exception of the sound-producing rattles of rattlesnakes.



Within its restricted range in the mountainous terrain of western Iran, P. urarachnoides inhabits rock crevices in the gypsum formations that comprise its hilly, arid habitat. Adaptations of the genus Pseudocerastes to desert life include supralabials (upper lip scales) with a serrated lower margin and a groove to accommodate the lower lip, which provide complete closure of the mouth and prevent sand from entering. The nostrils also have a valvular prominence to the same effect. The other two species of Pseudocerastes, P. persicus and P. fieldi, share these characteristics. These two species are sometimes combined, although differences in venom chemistry and scalation, along with the fact that their ranges are separated by the Zagros Mountains, suggest that they are probably distinct species (and they are certainly distinct morphologically from P. urarachnoides). Both overlap in range with P. urarachnoides in places.

P. urarachnoides

Two other recent and noteworthy discoveries of Old World pitvipers are worth a mention. One, Protobothrops mangshanensis, is a large and beautiful pitviper discovered in 1990 in mountainous regions in southern Hunan and reputed to be the only non-cobra capable of spitting venom. The other, Atheris matildae, discovered in 2011, is a member of an especially popular genus in the pet trade (although this could be said of many of the most beautiful vipers). The exact type locality of A. matildae, in the southern highlands of Tanzania, was concealed in order to limit collection for the pet trade. In addition, a novel strategy is being tested: A. matildae is being bred at a facility in Tanzania and the first few dozen offspring are being given away to collectors in order to reduce the market for illegally collected specimens. Whether this strategy will succeed remains to be seen, but hopefully A. matildae can be saved from the same sad fate as the Lao Newt, Roti Island Snake-necked Turtle, Chinese Leopard Gecko, coelacanth, and other species that have been overcollected almost as soon as they were described.

Atheris matildae
Protobothrops mangshanensis













Check out another amazing new snake discovery at Greg Laden's blog: once thought to be a single deadly sea snake, Enhyrina schistosa is actually two!

ACKNOWLEDGMENTS


Thanks to Heather Heinz for bringing P. urarachnoides to my attention, and to photographers and videographers Michael Kern, Behzad Fathinia, Michael & Patricia Fogden, Omid Mozaffari, and Alireza Shahrdari.

REFERENCES

Bostanchi H, Anderson SC, Kami HG, Papenfuss TJ (2006) A new species of Pseudocerastes with elaborate tail ornamentation from western Iran (Squamata: Viperidae). Proceedings of the California Academy of Sciences 57:443-450 <link>

David P, Tong H (1997) Translations of recent descriptions of Chinese pitvipers of the Trimeresurus-complex (Serpentes, Viperidae), with a key to the complex in China and adjacent areas. Smithsonian Herpetological Information Service 112:1-31 <link>

Fathinia B, Anderson SC, Rastegar-Pouyani N, Jahani H, Mohamadi H (2009) Notes on the natural history of Pseudocerastesurarachnoides (Squamata: Viperidae). Russian Journal of Herpetology 16:134-138 <link>

Fathinia B, Rastegar-Pouyani N (2010) On the Species of Pseudocerastes (Ophidia: Viperidae) in Iran. Russian Journal of Herpetology 17:275-279 <link>

Menegon M, Davenport T, Howell K (2011) Description of a new and critically endangered species of Atheris (Serpentes: Viperidae) from the Southern Highlands of Tanzania, with an overview of the country’s tree viper fauna. Zootaxa 3120:43-54 <link>

Stuart BL, Rhodin AGJ, Grismer LL, Hansel T (2006) Scientific description can imperil species. Science 312:1137 <link>
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Hot-spring Snakes

May 15, 2013, 8:31 am
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Everyone likes a good soak in a hot spring now and again, but imagine spending your whole life in one! Now imagine being the size of a pencil and unable to regulate your own body temperature, and you're doing a pretty good approximation of a Tibetan Hot-spring Snake (Thermophis). These tiny snakes reach only 2.5 feet in length and are found at fewer than ten sites on the Tibetan plateau in the Himalayan Mountains of south-central China, all above 14,000 feet elevation. For comparison, that's at least as tall as Mt. Rainier in Washington, Pike's Peak in Colorado, or Mont Blanc in the Alps. To cope with the cold, hot-spring snakes inhabit marshes, rivers, and rocky areas around sulfur-free hot springs, where they eat amphibians and fishes, including the dicroglossid frog Nanorana parkeri, the minnow Schizothorax oconnori, and elongate stone loaches in the genus Triplophysa. As you can see from this video, these are highly charismatic snakes.

Frank Wall
Hot-spring Snakes were first described in 1907 by a physician and herpetologist living in India named Frank Wall. Wall received specimens of this snake sent  from Tibet by Lieutenant F. M. Bailey, who reported that local people familiar with the snake told him that it could be found within half a mile of certain hot springs at any time of the year (although they did not enter the spring water). Wall was impressed by the altitude at which the snakes were found, which to date is still higher than any other snake known! Wall named the snake Natrix baileyi after Bailey, and in 1953 herpetologist Edmond Malnate moved it into a newly erected genus, Thermophis, meaning "heat snake" in Greek, giving it the name is has today: Thermophis baileyi. In 2008 a second species of Thermophis was discovered which differs slightly in scale characters and body proportions. Peng Guo of Yibin University named it Thermophis zhaoermii for preeminent Chinese herpetologist Zhao Ermi.

Just how remarkable these snakes are was not fully realized until recently. In the past, analyses of evolutionary relationships were limited to comparisons of morphological characteristics (for snakes, early taxonomists primarily relied on features of the scales and of the male reproductive organs, called hemipenes, to inform their hypotheses on how snakes were related to one another). Modern advances in molecular biology have enabled taxonomists to compare genetic sequences of related organisms and discover the intricate branching pattern of the evolutionary tree of life, essentially the family tree of all life on Earth. Although molecular phylogenetics, as this branch of science is called, is not flawless, it can provide incredible insight into the ancestry of species that have no close living relatives and therefore are very unique morphologically, making them difficult to compare with other organisms. Hot-spring Snakes are in this very situation, and although to a non-specialist they look pretty much like any other snake, their evolutionary history remained a mystery until 2009, when a group of biologists led by Zhao Ermi published two papers on the evolutionary origins of Thermophis.

Thermophis baileyi
As it turns out, Hot-spring Snakes are most closely related to South American snakes called xenodontines. Xenodontinae is one of the largest subfamilies of colubrid snakes, with about 90 genera and more than 500 species known. They are primarily tropical snakes previously thought to be restricted to the Americas, and they include several well-known (and many poorly-known) species, among them the South American Hog-nosed Snakes (genus Xenodon). Similarities of hemipenal morphology had hinted at a relationship between these taxa, but who would have guessed that the closest relatives of Hot-spring Snakes lived nearly 10,000 miles away on the tropical other side of the world? Not I, for one.

Thermophis baileyi
Hot-spring Snakes probably diverged from their "nearest" relatives about 28 million years ago. Despite the strengths of molecular phylogenetics, there is still some uncertainty about the position of Thermophis relative to other colubrid snakes because their branch of the tree arises near the base of a major clade (Xenodontinae), meaning that, as suspected, they have no close living relatives. In some phylogenies, Hot-spring Snakes are clustered with the "relict snakes of North America": Carphophis, Contia, Diadophis, Farancia, and Heterodon. Some of my favorite snakes, these are thought to have dispersed from Asia into North America during the Miocene, about 16 million years ago. (Diligent readers will recall that I've told this story before in my post on Rainbow Snakes, although I didn't know then about the involvement of Thermophis.)

Probably the common ancestor of all modern colubrids (Thermophis and NA relicts included) lived in Asia more than 30 million years ago. When the Bering Land Bridge connected North America and Asia, some of these snakes dispersed eastward across it, just like the ancestors of sabre-toothed tigers, woolly mammoths, and even Tyrannosaurus rex1. These evolved into a North American snake fauna, now largely extinct except for the few aforementioned relicts, and a hugely successful South American snake fauna, which was isolated from North America for a 5 million year period during the late Miocene-early Pliocene when the Isthmus of Panama was submerged by the ocean. One reason for this disparity is that two other groups of colubrid snakes, which are today the dominant colubrids of North America, the colubrines and the natricines, dispersed from Asia to North America around the same time as the xenodontines. Apparently ancestral colubrines and natricines dispersed more slowly than xenodontines, because they didn't reach South America before it separated. Instead, they only moved into South America following the most recent closing of the Isthmus of Panama in the late Pliocene, in an event known as the Great American Biotic Interchange. The GABI was responsible for allowing toads, treefrogs, opossums, armadillos, hummingbirds, and vampire bats to colonize North America, and salamanders, pit vipers, rabbits, squirrels, raccoons, deer, and jaguars (and colubrine and natricine snakes) to colonize South America. Assuming that Thermophis are all that's left of the original Asian proto-xenodontine snake stock, this pattern explains the evolutionary and biogeographic relationships of the Hot-spring Snakes and their relatives. However, given other recent discoveries in Asia, I wouldn't rule out the future discovery of another Asian proto-xenodontine more closely related to Thermophis than to any other known snake.

One reason we know only a little about Thermophis is its high mountain habitat. Most of the mountain ranges in China run east-west, but the Hengduan Mountains, where Hot-spring Snakes are found, stretch north-south (the name "Hengduan" means "to transect" and "cut downward" in Chinese). Parallel north-south sub-ranges of the Hengduans are separated by deep river valleys through which flow the famous Three Parallel Rivers: the Nujiang (Salween), Lantsang (Mekong), and Jinshajiang (Upper Changjiang or Yangtze). Thermophis baileyi is distributed west of the Salween, whereas T. zhaoermii is distributed east of the Changjiang. Geologic uplift of the intervening region of southern Tibet has lasted for about the last 20 million years, about the same age as the divergence between the two extant species of Thermophis. It is hypothesized that refuges in the Kyi Chu/Lhasa and Yarlung Zhangbo valleys during the last glacial maximum probably allowed T. baileyi to persist in the west, alongside such glacial relicts as neo-endemic ground beetles, juniper trees, and even humans. Following the end of the last Ice Age, they dispersed to other hot spring sites, and today connectivity among these sites is maintained when male snakes make rare movements among them, probably facilitated by the rivers and streams that connect the sites. Female snakes are less likely to disperse, because the plateau's short summers necessitate highly seasonal reproduction. Whether Thermophis are oviparous or viviparous is still unknown.

Although the advantages of living around hot springs at high altitudes, where the temperature is relatively cold, are pretty obvious, recent surveys by Ding-qi Rao found that Hot-spring Snakes also live in fields and other areas far from hot springs, suggesting that the species' ecological niche may be wider than previously thought. This is fortunate, both because the growing exploitation of geothermal energy has led to destruction and degradation of hot spring habitats, and because global climate change will likely continue to cause mountaintop habitats around the world to shrink, necessitating a shift upward in elevation by high-altitude species in order to follow their habitat. This problem has been documented for pikas and for birds and will likely affect Hot-spring Snakes too. Because the ability of mountaintop species to disperse across intervening areas to higher mountain ranges is limited, many may go extinct. Will we one day see the top of Mount Everest as the last foothold for Hot-spring Snakes? Let's hope not.


1 Not all of these dispersal events happened at the same time. Evidence suggests that the Bering Land Bridge has connected North America with Asia several times over the last seventy million years: at least once during the time of the dinosaurs, again about 55 million years ago, another 20-16 mya, and more recently both 35,000 and 22-7,000 years ago. The ancestors of the New World xenodontines probably came across 20-16 million years ago.↩


ACKNOWLEDGMENTS

Thanks to photographers Kai Wang, Daniel Winkler, Brian McDiarmant, and Gavin Maxwell for use of their photographs.

REFERENCES

Guo, P, Liu S, Feng J, He M (2008) The description of a new species of Thermophis (Serpentes: Colubridae). Sichuan Journal of Zoology 27:321 <link>

Guo, P., S. Y. Liu, S. Huang, M. He, Z. Y. Sun, J. C. Feng, and E. M. Zhao. 2009. Morphological variation in Thermophis Malnate (Serpentes: Colubridae), with an expanded description of T. zhaoermii. Zootaxa 1973:51-60 <link>

He M, Feng J, Zhao E (2010) The complete mitochondrial genome of the Sichuan hot-spring keel-back (Thermophis zhaoermii; Serpentes: Colubridae) and a mitogenomic phylogeny of the snakes. Mitochondrial DNA 21:8-18 <link>

Hofmann S (2012) Population genetic structure and geographic differentiation in the hot spring snake Thermophis baileyi (Serpentes, Colubridae): indications for glacial refuges in southern-central Tibet. Molecular Phylogenetics and Evolution 63:396-406 <link>

Hofmann S, Fritzsche P, Solhøy T, Dorge T, Miehe G (2012) Evidence of sex-biased dispersal in Thermophis baileyi inferred from microsatellite markers. Herpetologica 68:514-522 <link>

Huang S, Liu S, Guo P, Zhang Y, Zhao E (2009) What are the closest relatives of the hot-spring snakes (Colubridae, Thermophis), the relict species endemic to the Tibetan Plateau? Molecular Phylogenetics and Evolution 51:438-446 <link>

Pinou, T., S. Vicario, M. Marschner, and A. Caccone. 2004. Relict snakes of North America and their relationships within Caenophidia, using likelihood-based Bayesian methods on mitochondrial sequences. Molecular Phylogenetics and Evolution 32:563-574 <link>

Sekercioglu, C. H., S. H. Schneider, J. P. Fay, and S. R. Loarie. 2008. Climate change, elevational range shifts, and bird extinctions. Conservation Biology 22:140-150 <link>

Wall, F. 1907. Some new Asian snakes. The Journal of the Bombay Natural History Society 17:612-618 <link>
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Basics of Snake Taxonomy

May 28, 2013, 9:03 am
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A while back, medical-doctor-turned-snake-blog-post-translator-extraordinaire1 Alvaro Permartin asked me to write an article covering basic snake taxonomy. Taxonomy is the branch of biology that deals with naming and classifying organisms. Biologists still use the Linnean hierarchical system for taxonomy, which is convenient for grouping organisms, but there is a move towards using phylogenetic systematics and the evolutionary species concept in taxonomy, particularly in the sense that recognizing and giving names to non-monophyletic groups is discouraged.2 We'll primarily stick with the Linnean system in this article, which uses particular suffixes to denote the taxonomic level (for example, all animal families end in '-idae' and all subfamilies end in '-inae'). However, I've also included some cladograms, which are the most useful figures for understanding evolutionary relationships. If you haven't read one before, you can read up on them here, here, or here, but just know that they essentially work just like a family tree.

Snake Diversity

My sole criticism of this film:
not enough snakes
There are about 3,400 species of snakes in the world. All are placed in the suborder Serpentes (aka Ophidia) of the order Squamata, which also includes lizards, from which snakes evolved about 190 million years ago during the Jurassic Period. Extant (modern or living) snakes are divided into two major groups, the blindsnakes (aka threadsnakes or scolecophidians) and the advanced or true snakes (alethinophidians). Advanced snakes are also divided into two non-monophyletic groups, the "older snakes" (henophidians) and the "recent snakes" (caenophidians). The vast majority of all living snakes, about 77% or 2,650 species, are caenophidians, including most of the snakes you've probably heard of: rattlesnakes, cobras, kingsnakes, and many others. A few well-known snakes are henophidians, namely boas and pythons. Most scolecophidians are poorly known. Let's break down each of these groups in slightly more detail.

Scolecophidians

Ramphotyphlops braminus,
a parthenogenetic blindsnake
There are about 400 species of scolecophidians, divided into five families and found mostly in the tropics. They are commonly called blindsnakes, because many have vestigial eyes as a result of their fossorial lifestyle, or threadsnakes, because most are very thin. Most have unspecialized ventral scales, shed in thick rubbery rings, and have a spine at their tail tip. Many eat termites and ants. Most are probably oviparous, or egg-laying, but their reproductive biology is poorly known. Scolecophidians diverged from alethinophidians about 125 million years ago during the Cretaceous Period. You can read more about a fascinating mutualism between a blindsnake and an owl here, or about basic blindsnake biology here.


Phylogenetic tree showing currently accepted hypotheses of snake relationships. Figure from Lee et al 2007.
Thick lines are supported by both morphological and molecular studies, thin solid lines are supported
primarily by similarity of morphology, dotted lines are supported primarily by molecular analyses.



"Henophidians"

Anilius scytale
Red Pipesnake
"Henophidians" are a diverse, if species-poor, group of snakes. I mentioned earlier that they are non-monophyletic, meaning that some henophidians are more closely related to caenophidians than others, which is why the name of their group is in quotation marks. All henophidians shared a common ancestor about 98 million years ago, during the Cretaceous Period. There is some pretty major uncertainty about how henophidians are related to one another, but many taxonomies divide them into four superfamilies (which end in '-oidea' under the Linnean system). The most primitive, the Uropeltoidea, is comprised of five families (Aniliidae, Tropidophiidae, Anomochilidae, Cylindrophiidae, and Uropeltidae) that lack the ability to open their mouths very widely. These snakes have stout skulls with few lizard-like teeth, short tails, and poorly developed ventral scales. Most are viviparous, meaning that they give birth to live young, except the anomochilids, which are oviparous. There is better evidence linking the former two and latter three groups than there is for combining all five families together into a single superfamily. Also, two enigmatic species in the genus Xenophidion might belong somewhere in here.

Calabaria reinhardtii,
the Cameroon Burrowing Boa,
the only oviparous booid
The rest of the henophidians together with the caenophidians are often called the macrostomatans, because they have the ability to open their mouths (Greek: stomata) very wide and consume very large (Greek: macro) prey items. The most primitive of these are the oviparous Pythonoidea, a superfamily including true pythons (Pythonidae) as well as two small lesser-known groups respectively known as the Asian and Neotropical sunbeam snakes, the xenopeltids and the loxocemids. Pythonoids and a superficially similar but surprisingly unrelated group, the  viviparous booids (consisting of true boas and their less well-known relatives, the ungaliophine dwarf boas and the erycine sand boas),  diverged from other henophidians about 75 million years ago. Finally, the most advanced henophidians, the oviparous splitjaw snakes (aka Round Island "boas" or bolyeriids), diverged just slightly later than or around the same time as the true boas. Because the splitjaw snakes constitute only a single family and were historically considered boas, you don't usually hear them referred to as a fourth superfamily.

Caenophidians


Acrochordus granulatus
Little Filesnake
This huge group is divided into two superfamilies, called Acrochordoidea and Colubroidea. The first is small, containing only three species of Acrochordus, the filesnakes of southeast Asia and north Australia. These diverged from other caenophidians about 60 million years ago. The second is huge and there is some uncertainty about the relationships therein, although thanks to recent work by Alex Pyron and his colleagues, the picture is becoming more clear. Traditionally, colubroids have been divided into groups based on their tooth morphology: those with fixed fangs were placed into Elapidae, those with folding fangs into Viperidae, and those without fangs lumped into Colubridae. The first two of these groups have proven to be for the most part monophyletic, certain exceptions notwithstanding. However, a more nuanced and accurate view of colubroid snake taxonomy is emerging thanks to a combination of molecular tools and decades of careful work by snake morphologists. Ready for it? Here it is:

Figure from Pyron et al. 2011
These snakes are exciting! These snakes have venom, excellent color vision, and sophisticated chemosensory, prey acquisition, and antipredator abilities. Also they have spines on their hemipenes. Also they are awesome. Can you tell which group is my favorite?

Dendrelaphis punctulatus
Common Treesnake
The traditional three-family tooth-morphology arrangement of colubroids has been replaced by the seven family arrangement seen above. Three of those seven families include several subfamilies. The most primitive colubroids are the xenodermatids, or odd-scaled snakes, which diverged from the others about 47 mya. The snail-eating pareatids are next, a group you'll be familiar with if you've been following this blog since the beginning. Next diverged the viperids or vipers, about 35 million years ago. There are three subfamilies of vipers: the old world viperines, the widespread crotalines (or pit vipers), and the monotypic Azemiopsinae, or Fea's Viper. True colubrids are still a large group, even though many species have been removed to the "new" families. The subfamilies are large and diverse, although most lack dangerous venom (a few species notwithstanding). You can read the story of the evolution of some of the subfamilies here. There are many well-known colubrids, including ratsnakes, kingsnakes, racers, hog-nosed snakes, and many others. Homalopsids, including some that chew their food, are a small but interesting group of semi-aquatic snakes found in southeast Asia. The front-fanged elapids (including cobras and coral snakes) have retained their monophyly, and little support has been found for recognizing the sea snakes as a separate family. Finally, we have the Lamprophiidae, a new family erected to contain former colubrids that turned out to be closer relatives of elapids. Lamprophiids also represent several interesting subfamilies, including the side-stabbing atractaspines, scale-polishing psammophines, and Malagasy pseudoxyrhophiines. I think Darren Naish would agree that there's plenty of fodder for future articles in these groups.

One a closing note, some non-snakes that are commonly mistaken for snakes, primarily because they have no legs, include:
  • Legless lizards: There are several groups of legless lizards. The North American glass lizards are among the most familiar. All have external ear openings and most have eyelids. In one sense, snakes are but one very diverse group of legless lizards.
  • Amphisbaenians: These are also technically lizards, but under some older taxonomies they are referred to as a separate group of reptiles, because they have a vestigial right lung and have a unique skeletal structure.
  • Caecilians: These most primitive of amphibians have slimy skin and are found underground in the world's tropics. Many are common prey of coral snakes.
  • Eels: Elongate fishes that actually do have limbs in the form of fins. There are several groups of fishes that are all colloquially called eels, including spiny eels, fire eels, electric eels, and true eels (Anguilliformes). Some amphibians are also sometimes called eels, including amphiumas or conger eels, sirens or mud eels, and rubber eels, a kind of caecilian.
  • Worms: There are several different major groups of worms, including roundworms (nematodes), flatworms (platyhelminths), and segmented worms (annelids).
Snake taxonomy is a complicated field and there is still much disagreement among experts. I have made several oversimplifications above, so if this is your area of expertise feel free to chime in with a comment or two. I hope you're looking as forward to reading more about many of these groups as I am looking forward to writing about them.


1 His wife tells me that mediocre is actually more accurate↩



2 A monophyletic group is one that contains a common ancestor and all of its descendants. Examples include groups like animals, vertebrates, mammals, birds, amphibians, primates, and snakes. A non-monophyletic group is one that either omits some descendants (e.g., "reptiles", which does not include birds, or "fishes", which does not include tetrapods) or omits the common ancestor (e.g., warm-blooded vertebrates, which includes mammals and birds but not their cold-blooded common ancestor).↩


ACKNOWLEDGMENTS

Thanks to ptrick127, Gary Nafis, Tein-Shin Tsai, and Stephen Zozaya for use of their photos.

REFERENCES

Lee, M. S. Y., A. F. Hugall, R. Lawson, and J. D. Scanlon. 2007. Phylogeny of snakes (Serpentes): combining morphological and molecular data in likelihood, Bayesian and parsimony analyses. Systematics and Biodiversity 5:371-389 <link>

Pyron, R. A., F. Burbrink, and J. J. Wiens. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Biology 13. DOI: 10.1186/1471-2148-13-93 <link>

Pyron, R. A., F. T. Burbrink, G. R. Colli, A. N. M. de Oca, L. J. Vitt, C. A. Kuczynski, and J. J. Wiens. 2011. The phylogeny of advanced snakes (Colubroidea), with discovery of a new subfamily and comparison of support methods for likelihood trees. Molecular Phylogenetics and Evolution 58:329-342 <link>
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What the State Snakes Should Be: Part I

June 26, 2013, 6:57 am
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The 50 United States have various state symbols, including state trees, flowers, songs, drinks, and even fossils. Just over half the states have a state reptile, and none have a state snake (although a few of the state reptiles are snakes). This post was inspired by the witty and spot-on post 'The State Birds: What They SHOULD Be' from thebirdist.com, which struck a chord with me because I've always been underwhelmed by the state birds, many of which are uncreative and absurd. The selection of state reptiles has been characterized by the same lack-of-creativity, bordering on willful ignorance of a state’s unique and endemic biodiversity, as the selection of state birds. In fact, it's probably worse, since most people can at least name several different kinds of birds whereas even distinguishing reptiles from amphibians or fishes (or worms) is apparently beyond many. Perhaps having a state snake would help remedy this problem as well as improve upon the massive and undeserved PR problem faced by snakes in general.

At the risk of catalyzing a scandal on par with my home state of North Carolina's State Fruit Fiasco of 2001, which in an effort not to alienate any of several fruit growing lobbies resulted in an official state red berry (the strawberry), state blue berry (wait for it…the blueberry), and state fruit (the scuppernong grape), I've taken the liberty of choosing a state snake for each of the 50 U. S. states, 44 of which I've been to and almost half of which I've caught snakes in. This was surprisingly hard to do, because some snakes have too many good choices and others have too few. I used the same rules as thebirdist: I didn't repeat any species. Feel free to chime in with your opinion about what your state's snake should be, if it differs from my choice.

1. Alabama. Eastern Diamond-backed Rattlesnake (Crotalus adamanteus)

Crotalus adamanteus
The Eastern Diamondback is iconic in the southeast, appearing on America's first flag, the Gadsden flag (better known as the 'Don't Tread on Me' flag) and in the first political cartoon appearing in an American newspaper (Ben Franklin's 'Join, or Die'). State symbolism of the world's largest rattlesnake might help abate pressure from rattlesnake roundups in Alabama and other states, which have caused declines so serious that this species has been considered for listing under the Endangered Species Act.

2. Alaska. Northwestern Gartersnake (Thamnophis ordinoides)

Thamnophis ordinoides
Alaska's only got one snake, and I do mean one: a road-killed juvenile gartersnake was found outside of Haines, Alaska, in August of 2005. The poor condition of the specimen prevented a positive identification based on morphology alone, so some of my colleagues including my fellow USU graduate student Lori Neuman-Leesequenced genes from the snake and identified it as a T. ordinoides. This highly variable species eats mostly slugs. Because the closest known population of Northwestern Gartersnakes is over 600 miles south of Haines, the snake might have been transported there accidentally. However, reports of gartersnakes on the banks of the Taku and Stikine rivers in Alaska, including one ostensibly vouchered (now lost) specimen, keep the door open for future discovery of a naturally occurring population of snakes in The Last Frontier. Don't lose hope, Alaska! If nothing else, gartersnakes from British Columbia will probably disperse there eventually if climate change keeps up the way it's been going.

3. Arizona. Arizona Ridge-nosed Rattlesnake (Crotalus willardi)

Crotalus willardi
This actually is the state reptile of Arizona! Way to go, Arizona! This snake is a phenomenal choice for its beauty and uniqueness. Principally a Mexican species, it is found in scattered, isolated "Sky Island" mountain ranges separated by uncrossable desert. Former Staten Island Zoo reptile curator and herping godfather Carl Kauffeld, in his classic 1957 memoir Snakes and Snake Hunting, called this species "sublime" and said of finding one that "no greater triumph is possible". It was the last rattlesnake species discovered in the United States, in  1905 (just as the "Baby State," as it was once known, was one of the last states to enter the union, seven years after C. willardi was discovered). These small rattlesnakes grow to be only one to two feet long and as a result are relatively unthreatening. Few bites have been recorded, none serious, although I wouldn't go picking one up. Runner up: Glossy Snake (Arizona elegans), which shares its genus name with the state.

4. Arkansas. Cottonmouth (Agkistrodon piscivorus)

Agkistrodon piscivorus
When I asked my colleague Geoff Smith, a native Arkansan, about snakes iconic to Arkansas, he first informed me that, as someone born above the Arkansas River, he was an Arkansawyer rather than an Arkansan. He went on to suggest that the Cottonmouth was a good choice because every snake someone sees in Arkansas is identified as a Cottonmouth (a joke that is all too true, poor Nerodia). He also suggested some similarities between Arkansans and Cottonmouths: they stink, they're fat, they like to eat fish.1 In the end, we decided that a generalist state needed a generalist snake. Because Arkansas' diverse landscapes encompass the range edges of many species that are more characteristic of other places (for example, Queensnakes, Coralsnakes, and Western Diamond-backed Rattlesnakes can all be found in the state), choosing a widespread generalist is appropriate. I know of few better examples than the Cottonmouth, a denizen of river swamps that eats a variety of other vertebrates. Furthermore, Cottonmouths might have the worst PR problem of any snake: in addition to being misidentified, they suffer from exaggerated accounts of their aggression, size, breeding habits and even basking behavior ("A Water Moccasin tried to get in my boat!"). State snakehood might help with that.

5. California. Giant Gartersnake (Thamnophis gigas)

Thamnophis gigas
This largest of gartersnakes is endemic to California's Central Valley, where it historically occupied tule marshes but today persists mostly in rice fields and their associated canals and drains, where it mostly eats introduced fishes and Bullfrogs. Because of the massive agricultural use of this area, this species has lostmuch of its habitat and is on the edge of extinction, so it could use some positive PR. It is highly aquatic, with habits more similar to eastern Nerodia watersnakes than to its  western congeners - the same could be said of many Golden State residents in terms of their political opinions and attitudes.

6. Colorado. Great Plains Ratsnake (Pantherophis emoryi)

Pantherophis emoryi
Once considered a western subspecies of the Cornsnake, Great Plains Ratsnakes were re-elevated to full species status in 2002 by College of Staten Island snake taxonomist Frank Burbrink. Although Colorado's majestic landscapes are home to many beautiful snakes, not one but two geographically-separated forms of Great Plains Ratsnakes are found in the state: the larger, more brightly colored nominate subspecies in the high plains and tablelands of southeastern Colorado, and the smaller, drabber Intermountain Ratsnake (P. e. intermontanus) on the Colorado Plateau in the west-central part of the state. Originally named by Baird & Girard for surveyor and U.S. Army officer William H. Emory, these large constrictors are more subtly colored than other ratsnakes but just as harmless and beautiful.

7. Connecticut. Northern Watersnake (Nerodia sipedon)

Nerodia sipedon
Northern Watersnakes are some of the most common snakes in eastern North America. Found in almost every aquatic habitat, they are frequently seen basking on fallen logs, from which they will drop into the water at the slightest provocation. Leo Finneran reported this species from the Branford area in the 1940s, saying that it was "a very common snake occurring along water bodies in all parts of the town" and noting that some carried heavy loads of parasites, which is common in watersnakes. You can remember how to tell this species from its southern counterpart because the bands across its back fail to connect near the tail. OK, I'm stretching a bit for this one. Keep reading, it gets better.

8. Delaware. Copperhead (Agkistrodon contortrix)

Agkistrodon contortrix
Delaware was the first state, and the Copperhead is the first snake you should learn to identify if you live within its range. Delaware's Brandywine Valley is reminiscent of New England, whereas its middle and lower parts resemble the tidewater South. Both regions are inhabited by Copperheads, which are found from New York to Texas, where they are the most common venomous snakes in many suburban areas. Due to the high encounter rate, more than a third of U. S. venomous snakebites are from Copperheads. Fortunately, they seldom require antivenin, because they have the least potent venom of any North American viper, and the fatality rate is negligible. Furthermore, the vast majority occur when someone deliberately attempts to handle or kill the snake. In this way, Copperheads and their relatives are distinctly "antiwar," eponymous as they are of the vocal antebellum Democrats that once represented Delaware and other Union states in Congress.

9. Florida. Eastern Coralsnake (Micrurus fulvius)

Micrurus fulvius
Florida as a state is unlike any other U. S. state. Coralsnakes are unlike any other North American snakes - they are more closely related to cobras and sea snakes, which live on other continents or in the oceans. They're also brightly colored, like the iconic pink flamingos often seen on Sunshine State lawns. Coralsnakes spend most of their time underground and are difficult to find. When asked how to see one in the wild, most herpers reply: "Go to Florida." Although Coralsnakes are quite venomous, they are secretive and non-aggressive, so very few Coralsnake bites ever occur. Runners up: Short-tailed Snake (Lampropeltis [Stilosoma] extenuatum) or Rim Rock Crowned Snake (Tantilla oolitica), both endemic to the state.

10. Georgia. Eastern Indigo Snake (Drymarchon couperi)

Drymarchon couperi
The largest snakes in North America and literal "lords of the forest" (from the Greek drymos: forest and archos: commander), Eastern Indigo Snakes are in decline due to habitat loss and fragmentation. Georgia boasts some of the best remaining indigo habitat (both Fort Stewart and Fort Benning harbor large, unfragmented tracts of longleaf pine savanna with healthy populations of Gopher Tortoises, the actual Peach State reptile and the burrows of which these snakes depend upon) and the headquarters of the Orianne Society, a non-profit formed to help conserve indigo snakes and other rare reptiles.

11. Hawaii. Yellow-bellied Sea Snake (Pelamis platura)

Pelamis platura
This is the Aloha State's only native snake, making it a pretty easy choice. It's also awesome! Yellow-bellied Sea Snakes are the only pelagic snakes, and the most widely distributed and specialized of the sea snakes. They are most commonly seen in Hawaiian waters in El Niño years, when average water temperatures are in the upper 70s. Pelamis have fast-acting venom that they use to kill fishes. They shed their skin often to remove barnacles, using a knotting behavior to compensate for the absence of objects to brush against in the open ocean. Paying homage, a Scottish tidal energy company adopted the genus name of this snake for both their company and the offshore wave energy converter itself.

12. Idaho. Rubber Boa (Charina bottae)

Charina bottae
I've written about Rubber Boas before, but man are they cool. Some of the best research on Rubber Boa thermal biology and behavior was conducted in southeastern Idaho, and Craters of the Moon National Monument is a great place to see them. Incredibly, these snakes are active at temperatures as low as 40°F, which is good news for them given that they live in Idaho's mountains. Roughly the same color as a potato, Rubber Boas mostly eat small mammals, which they kill by constriction similar to their larger relatives, which include Anacondas and Boa Constrictors. As is fitting for the Gem State, their small, smooth scales have a rubbery shine.

13. Illinois. Prairie Kingsnake (Lampropeltis calligaster)

Lampropeltis calligaster
Illinois, like Arkansas, contains many ecoregions but is not dominated by any one that isn't more iconic of elsewhere. There are actually more species of snakes in Illinois than in many southern and eastern states, due to its mixture of northern, southern, eastern, and western ecosystems. I lived here for a while, but it was hard to pick a snake for Illinois because its habitats are so varied. Prairie Kingsnakes are common along Illinois roads and lake shores in spring. Unfortunately, many are run over by vehicles during this time, and still more are mistaken for venomous snakes are maliciously killed. In fact, these large and harmless constrictors are highly beneficial, consuming mice and voles that would otherwise overrun farms, gardens, and homes. In the agricultural desert of the Prairie State, Prairie Kingsnakes are one species that seems to do reasonably well.

14. Indiana. Eastern Ribbonsnake (Thamnophis sauritus)

Thamnophis sauritus
The slender, long-tailed ribbonsnakes share a genus with gartersnakes, from which they are not terribly different. Ribbonsnakes show a preference for wetter habitats and eat predominantly fishes and amphibians. Indiana harbors two subspecies of Eastern Ribbonsnakes, which together are found essentially throughout the state where suitable habitat still exists. Because of the Hoosier State's intensive agricultural land use, a state snake that requires intact wetlands with healthy prey populations could encourage a shift towards sustainable agricultural practices that use minimal pesticide and fertilizer and promote healthy waterways.

15. Iowa. Western Foxsnake (Pantherophis ramspotti)

Pantherophis ramspotti
These large constrictors used to be considered the same species as Eastern Foxsnakes, Pantherophis vulpinus, but were elevated to full species status by Brian Crother and colleagues in 2011. Rapid northward expansion by Foxsnakes from refugia in various southern states following the last glacial maximum has resulted in their odd modern distribution: two species apparently separated not by the gap in the range of the eastern in Michigan but by the Mississippi River. Because they no longer occupy any of the habitat where their fossils are found, it seems that Foxsnakes simply filled in the new habitat made available by the retreat of the glaciers. They had few barriers since the glaciers flattened the topography, and few states beat the Hawkeye State for flat.

16. Kansas. Milksnake (Lampropeltis triangulum)

Lampropeltis triangulum
The Red Milksnakes of Kansas are like jewels. Essentially fancy kingsnakes, these beauties are easy to find underneath large, flat rocks in prairies and fields almost throughout the state. They eat lizards as well as small mammals and other snakes, which should be easy for them to find since they all live under the same rocks. The late herpetologist extraordinaire Henry Fitch undertook detailed natural history studies of nearly every Kansas snake during his long and productive career, publishing hundreds of articles of the highest caliber, and his 1970 paper on milksnake ecology and natural history is no exception. About as popular as a snake can get, the Red Milksnake (L. t. syspila) is an easy choice for the state snake of the Sunflower State. All those states within the range of the Scarlet Kingsnake (L. t. elapsoides) only wish they weren't also home to so many other strong contenders.

17. Kentucky. Plain-bellied Watersnake (Nerodia erythrogaster)

Nerodia erythrogaster
Common elsewhere, a threatened subspecies of Plain-bellied Watersnake, the Copper-bellied (N. e. neglecta), is found in isolated spots in the western part of the Bluegrass State, as well as in adjacent areas in Illinois and Indiana. It is the most terrestrial of the ten species of watersnakes in the US, in part because it prefers frogs and toads to the other, more aquatic prey of its congeners. Uniquely among watersnakes, this species may possess resistance to toad toxin. It has been found that, atypically for a watersnake, these snakes tend to choose hibernacula close to wetlands, such as crayfish burrows and muskrat lodges. During spring floods, they are often submerged, but somehow are not drowned or swept away. The presence of these amazing snakes helps justify wetland buffers and adjacent upland conservation as part of the innovative Copperbelly Watersnake Conservation Agreement made between coal mining companies and state environmental groups within the range of the snake, particularly in Kentucky.

18. Louisiana. Louisiana Pinesnake (Pituophis ruthveni)

Pituophis ruthveni
Notable for its large eggs and small clutch sizes, the Louisiana Pinesnake is indigenous to west-central Louisiana and eastern Texas, where it relies strongly on Baird's pocket gophers for burrows and food. The Louisiana Pinesnake is rarely seen in the wild and is considered to be one of the rarest snakes in North America. The demise of the species is due to its low fecundity coupled with the extensive loss and degradation of suitable habitat, the longleaf pine savannas of the Gulf coastal plain. Now nearly a lost cause, some positive PR could help ensure that the last fragments of longleaf pine are preserved in perpetuity, for Louisiana Pinesnakes as well as their other unique flora and fauna.

19. Maine. Smooth Greensnake (Opheodrys vernalis)

Opheodrys vernalis
Although the Pine Tree State has a reputation for being snowy and cold, it is actually replete with snakes, at least in summer along its rocky coast. In the crumbling foundations of homes in old fields live many Smooth Greensnakes, a species that is a good example of the ecosystem services that snakes provide because it eats so many insects and spiders. Only a few species of snakes eat insects, this one chief among them. Less arboreal than their rough-scaled congeners, Smooth Greensnakes are quite beautiful and most people seem to know that they are harmless. A ranger in Acadia National Park found them "common" from sea level to above 1000 feet in 1938. Smooth Greensnakes are even found on Isle au Haut, a remote island in the outer reaches of Maine's Penobscot Bay first settled by Europeans in 1792, so it is likely that this is one of the first North American snakes ever seen by Europeans. Isle au Haut is home to Microneta bowditchiae, an endemic spider, which is undoubtedly eaten by the local O. vernalis.

20. Maryland. Queensnake (Regina septemvittata)

Regina septemvittata
Named for Queen Henrietta Maria of France and crisscrossed by myriad freshwater habitats, including the cool crayfish-filled streams preferred by Queensnakes, Maryland is a beautiful but densely-populated state. From the Central Appalachians in the west to the tidal marshes and barrier islands of the Delmarva peninsula and Chesapeake Bay, Maryland seems to represent the entire gamut of eastern North American habitats. Queensnakes inhabit most of these, although they are absent from the lowest and highest elevations and from brackish water. Research has shown that Queensnakes are exquisitely sensitive to the crayfish molting hormone ecdysone. Because numerous stream contaminants are known to imitate ecdysone and disrupt the arthropod molting cycle, this finding may have important implications for the conservation of Queensnakes and their conegners.

21. Massachusetts. Red-bellied Snake (Storeria occipitomaculata)

Storeria occipitomaculata
These little slug-eaters are named for a Massachusetts herpetologist, David Humphreys Storer, who wrote Report on the fishes, reptiles and birds of Massachusetts in 1839. Being one of the original 13 colonies, Massachusetts should show a little appreciation for its herpetological history. In my experience, these snakes are more common in New England's forests than they are throughout the rest of their range, particularly in Maine, which was once a part of Massachusetts. The Bay State gets kudos for actually selecting a group of snakes as their state reptile: the genus Thamnophis, the gartersnakes, is not an inapt choice, although it is a little vague.

22. Michigan: Eastern Massasauga (Sistrurus catenatus)

Sistrurus catenatus
The Eastern Massasauga Rattlesnake has declined dramatically over the last century and is critically endangered in nearly every state where it occurs. Due to human persecution and the nearly complete conversion of native wet prairie habitats to agriculture, this formerly widespread and abundant species is seemingly relegated to just a few viable populations within its historic range in Wisconsin and Illinois. Michigan is its stronghold, and state snakehood might help keep it that way.


23. Minnesota. Plains Gartersnake (Thamnophis radix)

Thamnophis radix
These beautiful gartersnakes are common in the plains of southern Minnesota. In northwestern part of the Land of 10,000 Lakes, the prairie-forest ecotone is characterized by the westward extension of the forests, which terminate roughly along the Big Stone Moraine, from which scattered areas of relict prairie form "fingers" that extend eastward into the woodland. Both Plains and Common (T. sirtalis) Gartersnakes co-occur there, but are not usually found together in high densities, perhaps because the diets of both species consist essentially of the same items: earthworms, minnows, and frogs. Unfortunately, Minnesota's many lakes (the combined shorelines of which exceed those of California, Florida, and Hawaii combined) are too cold, young, and oligotrophic to support any endemic snakes.

24. Mississippi. Mudsnake (Farancia abacura)

Farancia abacura
The Mississippi Mudsnakes has a good ring to it. Found in swamps, which abound in the western part of Mississippi, these gorgeous snakes eat mostly giant aquatic salamanders such as sirens and amphiumas. Seldom seen, their name belies their fabulous coloration, which more than compensates for their clandestine nature. Any state in their range would be proud to honor the Mudsnake with a state snakehood. Mudsnakes prefer still, acidic waters with aquatic vegetation and bottom debris. They also occur along small, acidic streams with swampy edges. Runner up: The Mississippi Green Watersnake (Nerodia cyclopion) shares its name with the state.

25. Missouri. Lined Snake (Tropidoclonion lineatum)

Tropidoclonion lineatum
Little is known about the tiny Lined Snake, a small relative of watersnakes and gartersnakes whose scientific name is longer than it is. Little is left of their original habitat, wet prairies, now mostly converted to agriculture. Lined Snakes, often incongruously misheard as "lion snakes," are secretive and semifossorial. The Forest Park neighborhood of St. Louis, south of the zoo and near the wonderful Turtle Park, was built on a hill during the 1920s and harbors a dense population due to the relatively light disturbance to the area's soil, so many urban residents of this city and others in the Show-Me State could show themselves their state snake by turning over paving stones or garden gnomes in their yard or garden.

Stay tuned, faithful reader, for Part II!


1 Life is Short but Snakes are Long does not officially endorse the views of interviewed persons.↩

ACKNOWLEDGMENTS

Thanks to photographers Dave Irving, JD Willson, Todd Pierson, James Turek, Lost Springs Ranch, Jason Folt, David Jahn, Jonathan Mays, Atrox, Eric Vanderduys, and Nathanael Herrera.
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What the State Snakes Should Be: Part II

August 9, 2013, 8:04 pm
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Several weeks ago, I debuted Part I of 'What the State Snakes Should Be', inspired by 'The State Birds: What They SHOULD Be' from thebirdist.com. With apologies for the late follow-up (I've been on vacation), I now present...

Part II

26. Montana. Bullsnake (Pituophis catenifer)

Pituophis catenifer
These large, harmless, common snakes are known for their loud hiss, which they augment using a flap of skin on the end of their windpipe. They also rattle their tail against dry leaves in order to intimidate their would-be predators. Also known as gophersnakes or blowsnakes, they are commonly mistaken for rattlesnakes, which they superficially resemble. Bullsnakes are found throughout the plains of central and eastern Montana, as well as in the Bitterroot Valley of western Montana. Appropriate to Big Sky Country, bullsnakes are among the longest of North American snakes, reaching incredible lengths of 9 feet as adults! Radiotelemetry studies have found that individuals spend up to 90% of their time in underground burrows, so these snakes must be quite abundant in areas where they are frequently encountered.

27. Nebraska. Western Hog-nosed Snake (Heterodon nasicus)

Heterodon nasicus
I studied these snakes in Illinois for my Master's degree, but nowhere have I seen them so abundant as in the Nebraska sandhills. Western Hognoses love sand, in which they burrow and lay their eggs. They also frequently unearth the buried eggs of other species, including those of lizards and turtles. Like their eastern cousins, they also eat amphibians and possess elaborate anti-predator displays. These snakes are easily observed in open areas during the day by anyone willing to hike around the beautiful sandhills region of the Cornhusker State.

28. Nevada. Desert Nightsnake (Hypsiglena chlorophaea)

Hypsiglena chlorophaea
Known for its nightlife, the Silver State is well-represented by Nightsnakes, which are secretive residents of deserts throughout the west. Nightsnakes are nocturnal, as evidenced by their vertical pupils, and eat lizards and amphibians, as well as lizard and snake eggs on occasion. They are most active on moonless nights after rain. Few people will have seen a Nightsnake, but they occur throughout Nevada. I also heard that the Nevada Nightsnakes might be a competitive team against the Mississippi Mudsnakes this year.

29. New Hampshire. Eastern Hog-nosed Snake (Heterodon platirhinos)

Heterodon platirhinos (dark phase)
Eastern Hognoses are well known for their elaborate anti-predator behavior, which involves vomiting, defecating, and flipping over onto their backs. Research in the southern part of the Granite State has shown that prey likely limits their distribution in the northeast, as they are found on barrier islands with small amphibians but not those without. A recent radio-telemetry study at the New Boston Air Force Station revealed much about the habitat preferences of these snakes. Overall optimal habitat was identified as hemlock forests having continuous canopy and understory architecture interspersed with fine-scale openings, in close proximity to wetlands and with a high density of leaf litter, debris, and rocks as well as homogeneous surface temperatures within critical thermal limits. Eastern Hognoses mostly eat amphibians and occur in two color phases, dark and patterned.

30. New Jersey. Northern Pine Snake (Pituophis melanoleucus)

Pituophis melanoleucus
Much of the pioneering research on pinesnake biology has taken place in the New Jersey Pine Barrens. We know a lot about the surprisingly social lives of these large snakes - for instance, they communally bury their eggs in habitual spots used year after year by the same females. Pinesnakes prefer sandy, well-drained soils such as those in the the New Jersey Pinelands, which may provide residence for some of the largest populations of pinesnakes in the Northeast. Their reputation as ornery is mostly undeserved, much like that of their fellow Garden State residents (something I can admit despite having been born in neighboring New York).

31. New Mexico. New Mexico Blindsnake (Rena dissectus)

Rena dissectus
Having just been to New Mexico, I know first-hand that there are a lot of snakes there to choose from. In the interest of representing the widest range of phylogenetic diversity, I decided that the New Mexico Blindsnake should represent the state, in part because I was fortunate enough to find one while I was there (my first wild scolecophidian!) and in part because they can be found in only a few states in the US. These diminutive serpents eat ants and termites and burrow in loose soil. This species was discovered by E. D. Cope in 1896 along a road to a silver mine at Lake Valley, New Mexico. Runners up: Narrow-headed Gartersnake (Thamnophis rufipunctatus), Mexican Gartersnake (Thamnophis eques), Chihuahuan Nightsnake (Hypsiglena jani), New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus).

32. New York. Brownsnake (Storeria dekayi)


Storeria dekayi
You might think the Empire State would be better typified by a grander snake, but there are several good reasons that Brownsnakes are special to New Yorkers (or should be). The first specimen of a Brownsnake was collected in New York by Dr. James DeKay, a zoologist and author of the 1842-1844 book Zoology of New York. He found the snake while it was ""swimming across a large bay on the Northern coast of Long Island." John Holbrook, the father of North American herpetology, named the snake for DeKay, making it the only North American snake whose name is a double patronym (the genus Storeria being in honor of David Storer, a Massachusetts herpetologist; see Massachusetts).

33. North Carolina. Southern Hog-nosed Snake (Heterodon simus)

Heterodon simus
Southern Hog-nosed Snakes aren't doing too well throughout most of their range. Habitat destruction and degradation, fire ants, and mortality on roads are among their major threats. The Sandhills of North Carolina are their stronghold, and we'd like to keep it that way. The North Carolina Herp Society supports Project Simus, a non-profit research program with the goal of monitoring Southern Hognoses in NC and learning more about their biology through radio telemetry and other techniques. North Carolina recently named a State Frog, a State Salamander, and a State Marsupial, so a State Snake could be next! Runners up: Carolina Pygmy Rattlesnake (the beautiful red phase) or Outer Banks Kingsnake or Carolina Watersnake (both endemic subspecies found in the barrier islands).

34. North Dakota. Racer (Coluber constrictor)

Coluber constrictor
Racers are one of North America's most widespread snakes, found in every state except Alaska and Hawaii. They are highly variable in color, ranging from brown to black to green to blue. In North Dakota, they are greenish-blue to gray with a bright yellow belly and a white chin patch. They aren't called Racers for nothing: their speed is astounding and it is common to see these snakes for just a second or two as you walk through a grassland. Racers inhabit the sagebrush prairies of western North Dakota and are commonly found near sources of water. They have large eyes which aid them in their pursuit of their prey during the day. Young racers have a distinctive speckled pattern that slowly fades as they mature. Due to their widespread nature, this species might be a good candidate for a national snake as well.

35. Ohio: Kirtland's Snake (Clonophis kirtlandii)

Clonophis kirtlandii
These small and interesting snakes were originally slated for Indiana, until I learned that not only were many of the seminal studies of them carried out in the Buckeye State and that they are named for an Ohio politician, malacologist, and co-founder of the Cleveland Museum of Natural History, Jared Potter Kirtland. Kirtland's Snakes are found only in the midwest, where they inhabit crayfish burrows. Because of the intensive agriculture that dominates rural areas of Indiana and other midwestern states, some of the best known Kirtland's Snake populations are found in urban areas. Runners up: Lake Erie Watersnake (an endemic subspecies), Black Racer (actual State Reptile).

36. Oklahoma. Western Diamond-backed Rattlesnake (Crotalus atrox)

Crotalus atrox
Much maligned symbol of the west, Western Diamondbacks are in much better shape than their slightly larger eastern cousins, in spite of heavy collection in some areas for use in rattlesnake roundups (festivals with the express purpose of executing as many rattlesnakes as possible in the misguided belief that this somehow makes people in the surrounding area safer). Corporate sponsorship and economic contributions to local economies have helped these festivals persist in the Sooner State and others, much to the detriment of wild rattlesnake populations. In fact, Western Diamondbacks and other rattlesnakes are not nearly as dangerous as cars, cigarettes, dogs, or many other things that people willingly accept as part of their lives. Granted, if one bites you you'd best get to the emergency room sooner than later, but they hardly deserve their vicious reputation, and confer many benefits to those with whom they share the landscape, including pest control.

37. Oregon. Common Gartersnake (Thamnophis sirtalis)

Thamnophis sirtalis
Although these snakes can be found in every state except Arizona, Hawaii, and Alaska, I have never seen more beautiful Common Gartersnakes than those in Oregon. Add that to the incredible coevolutionary relationship between these snakes and their toxic newt prey discovered in Oregon, and you have a good recipe for a state snake. Common Gartersnakes are capable of resisting the neurotoxic effects of tetrodotoxin, which paralyzes the muscles and nerves of most other predators. More resistant gartersnakes live in areas where newts are more toxic, are more brightly colored, and crawl more slowly.

38. Pennsylvania. Eastern Wormsnake (Carphophis amoenus)

Carphophis amoenus

It's tempting to put this smallest eastern snake for Rhode Island, but because it was discovered in the Keystone State by the famous Philadelphian and entomologist Thomas Say in 1824, I think it's more apt for Pennsylvania. Say described its opalescent scales and called it "a very pretty and perfectly harmless serpent," noting that "it is found beneath stones and prostrate logs, but not very frequently." Wormsnakes eat invertebrates and so are beneficial to have in and around your garden. Runner-up: Narrow-headed Gartersnake (Thamnophis brachystoma), found almost exclusively in Pennsylvania.

39. Rhode Island. Ring-necked Snake (Diadophis punctatus)

Diadophis punctatus
At least in the east, these snakes are small, with gorgeous yellow color beneath marked with black spots. Farther west, they are orange or red instead. The yellow ring around the neck gives the species its name. Described by Linnaeus in the 11th edition of his Systema Naturae, it was one of the first species of North American snakes known to European biologists. Ringnecks are usually found close to water underneath rocks and logs, although they rarely swim. Rhode Islands's many historic stone walls are ideal habitat for this species. Eating salamanders and invertebrates, these snakes are harmless and beneficial. Don't miss the playoff game between the Rhode Island Ringnecks and the Nevada Nightsnakes!

40. South Carolina. Cornsnake (Pantherophis guttatus)

Pantherophis guttatus
The Cornsnakes of the famous Okeetee Club of southern SC are famed for their bright colors. Popular pets, these snakes have been bred in captivity to produce a variety of color morphs not found in the wild. Cornsnakes eat lizards and small mammals and are named for their highly contrasting ventral pattern, which resembles an ear of Indian corn. Carl Kauffeld first wrote of the Okeetee Club in his book Snakes and Snake Hunting, wherein he recounts several of his experiences trying to find cornsnakes in their natural habitats.

41. South Dakota. Prairie Rattlesnake (Crotalus viridis)

Crotalus viridis
These rattlesnakes are fairly common in the Great Plains of the central USA wherever rocky outcrops (including man-made ones such as railroad track beds) provide suitable hibernation sites. They are closely related to Western Rattlesnakes (see Wyoming), with which they shared a common ancestor about 9 million years ago. Following their rise, the rain shadow of the Rocky Mountains fell over central North America, causing a drying of the climate that led to the gradual replacement of open woodlands by prairie. Differentiation of the eastern form involved isolation plus adaptation to the expanding grasslands east of the Rocky Mountains. Today Prairie Rattlesnakes are common across the western two-thirds of South Dakota, where they prey heavily on rodents.

42. Tennessee. Rough Greensnake (Opheodrys aestivus)

Opheodrys aestivus
Rough Greensnakes are beautiful denizens of riparian woods throughout the Volunteer State. They were first recorded from "Carolina", which included Tennessee at the time. Also known as vine snakes, these arboreal, camouflaged snakes eat insects and spiders. Because they are so well-camouflaged, the best way to spot them is often at night using a flashlight. Difficult to keep in captivity, I would volunteer to study these any time, as they are among the most graceful and popular of snakes.

43. Texas. Gray-banded Kingsnake (Lampropeltis alterna)

Lampeopeltis alterna
Texas has 85 species of snakes, more than any other state. I thought that Texans would like to have the longest or largest snake for their state snake (they'd probably call it their national snake), but both, as well as the largest rattlesnake, are more iconic of other places. As such, they will have to do with one of the most beautiful and coveted, the Gray-banded Kingsnake. These secretive snakes are found only in dry, rocky areas of the Trans-Pecos and Chihuahuan regions of the state, where they are active at night. Although popular in the pet trade, very little is known about the ecology of these snakes in the wild. Much of their habitat is inaccessible, made more so by strict laws regulating the recreational pursuit of snakes (herping or snake-hunting) in the state of Texas. Runners-up: Speckled Racer (Drymobius margaritiferus), Concho Watersnake (Nerodia paucimaculata), Brazos Watersnake (Nerodia harteri), Texas Indigo Snake (Drymarchon corais).

44. Utah. Wandering Gartersnake (Thamnophiselegans)

Thamnophis elegans
Because I currently live in Utah, I can attest to the ubiquity of these snakes almost throughout the state. So named because of their propensity to stray far from water, Wandering Gartersnakes have something in common with the early Mormon settlers of the Beehive State, who emigrated from their original homeland in New York through the Midwest to eventually end up in what is today Utah. Wandering Gartersnakes eat fish, frogs, and small mammals, and lack the resistance of some of their congeners to newt toxin because they do not co-occur with newts over much of their range.

45. Vermont. Black Ratsnake (Pantherophis obsoletus)

Pantherophis obsoletus
Familiar to many in the eastern US, ratsnakes are on the ropes in Vermont. Records from the west-central part of the state date from recent decades, with possible isolated populations in other areas of the Green Mountain State (though these records could represent releases of captive animals). Ratsnakes have been designated a Species of Greatest Conservation Need in Vermont’s Wildlife Action Plan. Popular in captivity, we are just beginning to learn about the ecology of wild ratsnakes, which are highly accomplished climbers and important nest predators. Their communal nesting ecology at high latitudes and their intriguing foraging and social behaviors are likely just the tip of the iceberg.

46. Virginia. Smooth Earthsnake (Virginia valeriae)

Virginia valeriae
These small brown snakes come in two types, rough and smooth. The Rough Earthsnake (Virginia striatula) is found in the southeastern part of the state, whereas the more widespread Smooth Earthsnake (Virginia valeriae) is found across the eastern two-thirds, and also in isolated populations in the western tip. Virginia also shares with adjacent states an unusual population of Smooth Earthsnakes, called Mountain Earthsnakes (V. v. pulchra or, sometimes, simply V. pulchra), found in high-altitude glades in Highland County, Virginia, and adjacent WV, MD, and PA. Mountain Earthsnakes have scale characteristics intermediate between the other two, although they are more closely related to Smooth Earthsnakes.

47. Washington. Sharp-tailed Snake (Contia tenuis)

Contia tenuis
Sharp-tailed Snakes are small and locally common. They are named for the needle-like spine on the end of their tail, which nevertheless is not actually very sharp and with which they certainly cannot harm a human. This is a good snake to have around your garden, as they eat slugs and other invertebrates harmful to plants. Sharp-tails are mostly found in Oregon and California, but an isolated population occurs in central Washington, where dozens of individuals can sometimes be found together underneath cover objects. Sharp-tailed Snakes may turn out to be more widespread in Washington, especially since they were first discovered in 1852 by members of the U.S. Exploring Expedition near Puget Sound, a region from which no further specimens have been found. Perhaps state snakehood would promote further exploration.

48. West Virginia: Timber Rattlesnake (Crotalus horridus)

Crotalus horridus
Kudos to West Virginia for choosing a snake for their state reptile in real life! As a reward, they get to keep it. The Timber Rattlesnake isn't an inapt choice, as they are found in mountainous forests almost throughout the state, wherever suitable overwintering habitat exists. A recent analysis of the diet of Timber Rattlesnakes in the northeastern US suggested that they may help regulate tick populations through consumption of their mouse hosts, thereby probably reducing the risk of human exposure to Lyme disease and other tick-borne pathogens. Runner up: the other (Rough) Earthsnake (Virginia striatula).

49. Wisconsin. Butler's Gartersnake (Thamnophis butleri)


Thamnophis butleri
Butler's Gartersnakes are found in open-canopy wetlands in the southern Great Lakes region. In reality, enough Wisconsinites hate Butler's Gartersnakes for getting in the way of development in the Milwaukee area that it would probably never get chosen for the state snake. It'd be like having the Spotted Owl as the state bird of Oregon. However, efforts to manage and preserve the remaining habitat might just succeed, and could be significantly helped along by placing a little more value on these little snakes. In the land of visionary land manager Aldo Leopold, I agree with this One Wisconsin Now blogger that good stewardship should trump special interests when it comes to Butler's Gartersnakes.

50. Wyoming. Western Rattlesnake (Crotalus oreganus)

Crotalus oreganus
These relatively small rattlesnakes are fairly common in the arid west anywhere that rocky outcrops provide suitable hibernation sites. They are closely related to Prairie Rattlesnakes (see South Dakota). These two species shared a common ancestor about 9 million years ago, populations of which were separated by the rise of the Colorado Plateau during the Miocene epoch. Volcanic activity in the southern area of the plateau prevented contact between the two populations. Further differentiation of the western form into six subspecies involved adaptation to various cooler climates west of the Rocky Mountains. Two subspecies, the Great Basin and Faded Midget Rattlesnakes, occur in the Cowboy State today.

Feel free to chime in with your opinion about what your state's snake should be, if it differs from mine. What do you think the National Snake would be, if the USA had one? Vote in the poll at the right, or share your opinion in the comments below. If you missed Part I, check it out!

ACKNOWLEDGMENTS

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Pelagic Sea Snakes and the animals that live on them

August 27, 2013, 6:03 am
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This overdue post was inspired by the symposium ‘‘New Frontiers from Marine Snakes to Marine Ecosystems’’ presented at the annual meeting of the Society for Integrative and Comparative Biology, January 3–7, 2012 at Charleston, South Carolina, and featured in a special issue of the journal of the same name.

Head of a Pelagic Sea Snake, Pelamis platura
I've written before about some of the amazing aspects of sea snake biology. From the morphological and physiological to the behavioral and reproductive, few sea snake adaptations cease to amaze. But one topic I had never before considered was marine snake parasitology. I knew that the skin of whales, the shells of sea turtles, the hulls of ships, and other mobile pelagic surfaces often serve as a substrate for smaller, more sessile marine organisms, such as barnacles, collectively known as epibionts. In fact, I recently learned that the total weight of all the barnacles on a single Gray Whale can exceed seven hundred pounds and that these barnacles serve as homes for other, more parasitic hitchhikers such as whale lice. But I had never heard of marine reptiles other than sea turtles harboring parasites.

The range of the Pelagic Sea Snake, which is
the world's widest ranging species of snake
I was surprised to learn that many marine snakes play host to epibionts. Twenty-eight of the ~65 species of sea snake have been documented to harbor at least one kind of epibiont. But one species, the Pelagic or Yellow-bellied Sea Snake (Pelamis platurus [sometimes platura]), harbors more kinds of epibionts than any other. In order to understand why, it is helpful to know that Pelamis platurus is found farther out in the open ocean than any other kind of sea snake. Most species of sea snake stick relatively close to reefs and shores in the Indian and Pacific Oceans, but Pelagic Sea Snakes are found from the east coast of Africa across the tropics to the west coast of the Americas. They are the only exclusively pelagic marine snake, meaning they live near the surface of the ocean but far away from land, and their distribution spans more than half of the Earth's circumference, making them the most widely distributed snake on Earth.

Artist's rendition of "float-and-wait" foraging.
I was unable to find a photograph of this behavior.
If you know of one, please let me know.
Digital painting by Stuart Jackson-Carter; www.sjcillustration.com
Although there is some debate about the amount of intent used to get there, Pelagic Sea Snakes sometimes congregate around clam areas where ocean currents converge, ("slicks"), where flotsam, debris, and pelagic organisms are often concentrated. By one 1519 explorer's account, Pelagic Sea Snakes were "innumerable" along one such slick on the west coast of Costa Rica. Pelagic Sea Snakes are "float-and-wait" predators, meaning that they passively drift in the water waiting for fishes to come near. A similar strategy is used by many terrestrial snakes, such as vipers and large pythons, except that in the open ocean, many fishes probably approach purposefully, meaning to take shelter beneath the seemingly inanimate snakes. The snakes then strike sideways or by swimming rapidly backwards. Their venom, like that of most sea snakes, is made up of only one or two exceptionally potent compounds, unlike the complex venoms of most terrestrial snakes. Partially as a result of their biodiverse habitat and immobile foraging behavior, Pelagic Sea Snakes play host to a diversity and abundance of epibionts almost twice as great as that of any other kind of sea snake.

Crustacean epibionts from Pelagic Sea Snakes
Most marine snake epibionts are invertebrates. Barnacles are ubiquitous, and familiar marine creatures such as crabs, shrimp, snails, and oysters are also found living on sea snakes, alongside more obscure marine animals such as hydrozoans (hydras) and bryozoans ("moss animals"). Polychaete worms and ticks round out the epibiont fauna, and algae, diatoms, and a type of protist called foraminiferans ("forams" for short) represent a sort of flora, although none of these organisms are true plants. Most amazing to me are two chordates, a tunicate and a clingfish, that were recently documented as epibionts of Pelagic Sea Snakes. Tunicates, also known as sea squirts, are marine filter feeders that have a sac-like body structure as adults. Tunicate larvae are free-swimming and resemble tadpoles, but at metamorphosis an adhesive disc on their "head" transforms into a stolon, or "foot", which they use to cling to a rock or, in this case, a sea snake. The pelvic fins of clingfishes are modified into a sucking disc, which they use to hold onto their snake hosts. How they avoid being eaten, I do not think anyone knows yet.

In order to keep this menagerie under control, Pelagic Sea Snakes shed frequently. On average, a Pelagic Sea Snake will shed its skin once every two weeks, whereas most other snakes go for one to two months between sheds. Additionally, while in most snakes the frequency of shedding decreases with age, it remains frequent into adulthood in Pelagic Sea Snakes. Because the open ocean is devoid of surfaces against which to rub to facilitate shedding, Pelagic Sea Snakes use a behavior known as "knotting" to initiate the process and to remove the shed skin and any associated epibionts. You can see a good example of knotting behavior in this video of a captive Pelagic Sea Snake:



Pelamis platurus never leave the water
and cannot move on land. Most that land on beaches die.
Why do so many animals live on Pelagic Sea Snakes? One explanation may be the protection associated with settling upon one of the world's most venomous serpents. Pelagic Sea Snakes are not eaten by most seabirds or fishes (even naive Atlantic fishes spit them out) and so neither are their epibionts. Perhaps natural selection has favored the crabs, barnacles, and tunicates that live on sea snakes over those that land on more palatable substrates. Furthermore, the complex interplay among various members of the sea snake epibiont community may allow more species to coexist there. For instance, predatory epibionts such as larval crabs may benefit the sea snakes by controlling populations of other, more detrimental epibionts, such as barnacles, which probably slow or block the update of oxygen by the snake's skin during long dives.

Sea snakes are among the most amazing of serpents, and Pelagic Sea Snakes are among the most amazing of sea snakes. From their saffron bellies to their lung, used to control buoyancy, to their roles as substrates for unique ecosystems, these snakes might just be the most incredible snakes out there.

ACKNOWLEDGMENTS

Thanks to William Flaxington, Hung-Jou Chen, Chayajit, and Stuart Jackson-Carter for their photos and digital illustrations, and to Joe Pfaller for answering my questions about sea snake epibionts.

REFERENCES


Brischoux, F. & H. B. Lillywhite (2011). Light-and flotsam-dependent ‘float-and-wait’foraging by pelagic sea snakes (Pelamis platurus). Marine Biology 158:2343-2347 <link>

Castro, J. J., J. A. Santiago & A. T. Santana-Ortega (2002). A general theory on fish aggregation to floating objects: An alternative to the meeting point hypothesis. Reviews in Fish Biology and Fisheries. 11:255-277 <link>

Graham, J. B. (1974). Aquatic respiration in the sea snake Pelamis platurus. Respiration Physiology 21, 1-7 <link>

Greene, H. W. (1997) Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press <link>

Pfaller, J. B., M. G. Frick, F. Brischoux, C. M. Sheehy, and H. B. Lillywhite. 2012. Marine snake epibiosis: a review and first report of decapods associated with Pelamis platurus. Integrative and Comparative Biology 52:296-310 <link>

Rubinoff, I. & C. Kropach (1970). Differential reactions of Atlantic and Pacific predators to sea snakes. Nature 228, 1288-1290 <link>

Zann LP, Cuffey RJ, Kropach C. 1975. Fouling organisms and parasites associated with the skin of sea snakes. In: Dunson WA, editor. The biology of sea snakes. Baltimore: University Park Press. p. 251–65


POSTSCRIPT

Cetacean photographer Eduardo Lugo captured this image of a Pelagic Sea Snake being pushed up out of the water by a dolphin, almost as if it was riding on its back:


Perhaps Pelamis is heading towards a lifestyle as a dolphin epibiont? Doubtful, but an amazing image nonetheless.

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Dragonsnakes

September 10, 2013, 8:06 am
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This post will soon be available in Spanish!


Head of Xenodermus javanicus
One of the weirdest-looking snakes in the world is Xenodermus javanicus, also called the Javan Tubercle Snake, Javan Mudsnake, Rough-backed Litter Snake, or, best of all, the Dragonsnake. Although they don't breathe fire, their anatomy is strange enough to evoke images of mythical creatures. The first Dragonsnake was described in 1836 by Danish zoologist Johannes T. Reinhardt. He named it Xenodermus, Greek for "foreign skin", because of its peculiar scales, of which Reinhardt described three types. A triple row of large keeled scales runs down the center of the back, flanked by two rows of huge keeled tubercles that resemble crests more than scales. The gaps between these knobby rows are covered in small irregular smooth diamond- and pentagon-shaped scales, whereas the space below the tubercles is coated in more traditional parallel rows of keeled dorsal scales, which nevertheless resemble a highly organized bed of oysters more than typical colubrid scalation.

Dorsal scales of Xenodermus javanicus
Given the dorsal side only, it's difficult to tell what the taxonomic relationships of Dragonsnakes are. However, you can tell this snake is a colubroid if you examine the ventral side, where wide, well-developed ventral scales are present, unlike the smaller ventral scales of more primitive snakes. The tail, which constitutes up to a third of the total length, has a single row of scales on the underside, a characteristic reminiscent of vipers but also found in some colubroids. Overall, the head is probably the weirdest attribute. The top, sides, and bottom of the head are covered by small granular scales, similar to those of pythons and other henophidians. But a few specialized scales grace the nose and lips of Dragonsnakes. These include about 20 labial scales, a small rostral scale at the tip of the nose (impossible to see from above), two large nasal scales, directed forward, enclosing the nostrils, and several small shields in the vicinity of these nasal scales, separated by bare skin. What are all these weird scales for? Why didn't Dragonsnakes evolve more specialized scales, like the other descendants of their common ancestor with colubrids? These are open questions, but the Dragonsnake's environment probably has something to do with it. Another rare Bornean reptile, the Earless Monitor Lizard (Lanthanotus borneensis), has a similar mixture of high- and low-entropy scalation.

Ventral side of Xenodermus javanicus
Dragonsnakes' closest relatives are 16 species of obscure snakes in 4 genera that together make up the family Xenodermatidae. Xenodermatids occupy a position similar to that of pareatids, near the base of the colubroid family tree. Traditionally, both xenodermatids and pareatids were considered subfamilies of the "junk family" Colubridae, but recent phylogenetic analyses all agree that they are only distantly related to other Colubridae, and must therefore be recognized as separate families. Xenodermatids are the most distantly related colubroids, or the "sister group" to all other colubroids, having diverged nearly 50 million years ago at the beginning of the Cenozoic, four times closer to the extinction of the dinosaurs than to today.

Xenodermus javanicus
Dragonsnakes are found in southeast Asia, including southern Burma and Thailand and peninsular Malaysia, as well as on the islands of Borneo, Sumatra, and Java. Although this area was once connected, the isolation of the islands and mainland has probably resulted in geographic isolation among populations of Dragonsnakes. Although no study to date has examined either morphological or genetic differences among Dragonsnakes from different islands, I wouldn't be surprised to see them split up into multiple species once this information eventually becomes available. We know a little about the ecology of Dragonsnakes in the wild. They are active at night, when they hunt for frogs along rocky streams in tropical rain forests, as well as in rice fields. They lay several clutches of 2–4 eggs each year during the rainy season, from October to February. The young hatch after an incubation period of about two months. Apparently when you grab one, it freezes, holding its body stiff, a behavior which you can see well in this video, taken by field herpers in Indonesia.

Dragonsnake plate from Dumeril's Erpetologie Generale,
showing in detail the scale anatomy.
This plate hangs on the wall in my dining room.
Apparently Dragonsnakes are increasing in popularity in the pet trade, so we may learn more about certain aspects of their biology through the keeping of captive individuals. Hopefully collection from the wild will be kept to a minimum, and somebody one day will conduct a detailed study of Dragonsnake ecology.

ACKNOWLEDGMENTS

Thanks to Tom Charlton, Mister Pupkin, and LOB for use of their photographs.

REFERENCES

de Rooij, N. (1917) The Reptiles of the Indo-Australian Archipelago. Il. Ophidia. Leiden: E. J. Brill <link>

Kopstein, F. 1938. Ein beitrag zur morphologie, biologie, und ökologie von Xenodermus javanicus Reinhardt. Bulletin of the Raffles Museum 14:168-174. <link>

Reinhardt, J. T. 1836. Afhandling om Xenodermus javanicus. Oversigt over det Kongelige Danske videnskabernes selskabs forhandlinger. Kjobenhavn 3: 6-7 <link>
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Basics of Snake Fangs

September 25, 2013, 7:46 am
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Solenoglyphous fangs of a Gaboon Viper
Snake fangs are specialized, elegantly modified teeth. Some are like hypodermic needles, others are more like water slides. But all serve essentially the same purpose: to inject venom into the snake's prey. Occasionally, the fangs are also used in defense, but studies show that snakes striking in defense are far less likely to inject venom than when they're striking at a prey item, a fact that has assuaged the fears of many an ophidiophobic. I wanted to write a brief review of snake fang types, because their anatomy is very interesting and also because of their important role in classifying snakes and understanding how different groups of snakes are related to each other.

Cross-sections of fangs:
F is an aglyphous tooth.
G is an opisthoglyphous fang.
H is a proteroglyphous fang.
I is a hollow solenoglyphous fang.
From Bauchot (2006)
Many snakes produce venom, which is essentially very strong saliva, in glands in their heads (which is where you produce your saliva, too). We call these glands venom glands if they are well-developed, complete with an interior cavity, a duct connecting to a hollow fang, and compressor muscles that generate high pressures when the jaws are rapidly closed. If they lack these features, we usually call them Duvernoy's glands instead. Because there is a lot of variation among snake species in the structure of these glands and their associated teeth, there is some debate about whether or not venom glands and Duvernoy's glands are really two forms of the same thing. Either way, three groups of snakes (atractaspidines, elapids, and viperids) have independently evolved an advanced apparatus to deliver large quantities of venom during a brief strike, and many other snakes (and a few lizards) have evolved less sophisticated, but still relatively effective, modifications to their teeth in order to deliver venom after they have grabbed their prey and are "chewing" on it. The teeth of modern snakes are classically divided into four types, three of which are typically called fangs. The four tooth types have fancy names, all of which involve the Greek word glyph, one of the meanings of which is "groove". They are as follows:

Solenoglyphous

Folding of solenoglyphous fangs.
Fang is in red, maxilla green,
prefrontal orange, pterygoid yellow,
ectopterygoid purple. Vipers lack
premaxillary and palatine teeth.
From Bauchot (2006)
This most sophisticated fang type evolved once, in the ancestor to all modern vipers, which lived in Asia about 40 million years ago. Fossils suggest that solenoglyphous fangs have changed little since that time, even though vipers have undergone an incredibly successful radiation into 320 extant species found on all continents except for Australia and Antarctica. Solenoglyphous fangs are long and tubular and are attached to the snake's maxillary bone. Most snakes have several tooth-bearing bones, including four (the premaxilla, maxilla, pterygoid, and palatine) in the upper jaw, and one (the dentary) in the lower. In humans, three of these bones (the premaxilla, maxilla, and dentary) also bear teeth - your premaxilla holds your top incisors, while your maxilla holds your upper canines and molars and your dentary all your lower teeth - while the others form part of the roof of the mouth. In vipers, the maxilla bears only a single tooth (the fang) and is hinged so that the fangs can be folded back parallel to the jaws when the mouth is closed, or erected perpendicular to the jaws, the position when striking. The teeth in the pterygoids and dentaries work together to manipulate food once it gets into the mouth. Solenoglyphous fangs are strikingly similar to hypodermic needles. They have a hollow core that receives venom from the venom gland at the entrance orifice near the base and injects it from a slit-like exit orifice on the front of the fang near the tip. If the opening were at the very tip of the fang, its strength would be compromised and it would lack the sharp point needed to penetrate the target. Even under normal use, vipers shed their fangs every two months.

Modified solenoglyphous fang of
African Burrowing Asp (Atractaspis engaddensis)
A similar fang type evolved a second time about 29 million years ago in a group of African snakes, currently placed in the family Lamprophiidae, subfamily Atractaspidinae. Two genera, Atractaspis(mole vipers, burrowing asps, or stiletto snakes) and Homoroselaps (African dwarf garter or harlequin snakes), possess elongate anterior fangs, although only those of the stiletto snakes are movable. Stiletto snake fangs pivot on a socket-like joint that is more flexible than those of vipers, allowing these snakes to strike beside and behind them with their mouth closed. This is an adaptation to living underground and envenomating small mammals and other reptiles in narrow subterranean burrows. The fang morphology of atractaspidines and viperids is remarkably similar, considering that these two snake lineages last shared a common ancestor over 40 million years ago.

Proteroglyphous

Proteroglyphous fangs of an Eastern Green Mamba
(Dendroaspis angusticeps). Don't try this.
From Bauchot (2006)
This fang type also evolved only once, in the ancestor to all modern elapids, which lived 11 mya in Asia or Africa. Proteroglyphous fangs are in the front of the mouth and are about three times shorter than solenoglyphous fangs. This is because they are not hinged. Snakes with proteroglyphous fangs typically strike their prey and hang on until the venom has taken effect, as opposed to releasing they prey and then tracking it down. Some elapids constrict their prey at the same time as envenomating it. Over 350 species of elapids exist today, including well-known groups such as cobras, mambas, death adders, taipans, coralsnakes, and sea snakes, and less-well-known species, mainly found in Australia, of which a good number are small, secretive, and not considered dangerous to humans.

Maxilla of a proteroglyphous snake showing the almost
completely closed groove along the anterior edge connecting
the two orifices, as well as the aglyphous tooth at the
rear of the maxilla. This line may be obscured in longer fangs.
From Shea et al. 1993
Unlike solenoglyphs, some proteroglyphs have other teeth on the maxilla behind the fang. However, the fang is always separated from the other teeth by a gap, called a diastema. Some elapids have more than one functional fang on each side. In both vipers and elapids, there are usually at least two fangs on each maxilla at any one time, one that is in use and one that is a reserve fang. Both fangs are draped in a layer of connective tissue and skin called the fang sheath. Some proteroglyphs have partially movable fangs, including many of the most dangerous species such as mambas, taipans, and death adders. A few, such as spitting cobras, have modified exit orifices to their fangs that are smaller and rounder than in other cobras, a modification that increases the velocity with which venom is ejected. Modifications to the muscles and the fang sheath also facilitate spitting in these cobras. A few elapids, such as sea snakes that eat only fish eggs, have lost their fangs and their venom glands, which suggests that the primary role of venom, at least among elapids, is in feeding rather than in defense.

Opisthoglyphous

Opisthoglyphous fang of Eastern Hog-nosed Snake
These are commonly known as "rear-fanged" snakes. Opisthoglyphous fangs are grooved rather than hollow and are found near the back of the maxilla, behind the normal teeth. Typically, snakes with rear fangs must chew on their prey to bring their fangs into a biting position. There is considerable variation in the size, shape, and number of opisthoglyphous fangs from species to species, and sometimes even within a species. Most opisthoglyphous fangs are connected to Duvernoy's glands, which differ from true venom glands in several important ways, most notably in that they lack associated muscles to generate the pressure needed to evacuate venom, as in solenoglyphous and proteroglyphous snakes. The pressure on the venom glands of biting solenoglyphs and proteroglyphs can exceed 30 psi, the pressure of a car tire, whereas the pressure inside the Duvernoy's glands of opisthoglyphs is generally less than 5 psi. Because Duvernoy's glands also lack a chamber for storing venom, the idea is emerging that opisthoglyphous snakes probably secrete their venom only during chewing, which explains why prolonged bites by opisthoglyphs generally have more severe effects.

Opisthoglyphous fangs of Boomslang (Dispholidus typus)
Don't do this either.
Most of these snakes are not harmful to humans, with a few notable exceptions. Boomslangs and Twigsnakes are arboreal, diurnal African colubrines that prey on lizards and birds. They have short heads, rear fangs situated comparatively close to the front of the mouth, and partially muscled Duvernoy's glands. They also have potent venoms and their bites have killed several people, including two prominent snake biologists, Karl Schmidt and Robert Mertens. Bites from other rear-fanged snakes are known to cause relatively mild, transient, and local symptoms, but clinical documentation of these bites and their effects is scattered, incomplete, and frequently anecdotal. Many are written by the victim themselves! The above notwithstanding, bites from opisthoglyphs are generally less medically important than those from proteroglyphs and solenoglyphs. As a result, snake venom research has not focused on them, so there is still much that we do not know about this group of snakes, some of which are becoming increasingly common in the pet trade. Based on what little we do know, the composition of opisthoglyph venom/Duvernoy's secretion is fairly similar to that of viperids, elapids and atractaspidines, which makes sense given that each of these groups is more closely related to certain opisthoglyphs than they are to one another.

A: python, B: viper, C: rear-fanged colubroid, D: cobra
The f  marks the portion of the maxilla where the fang develops.
E shows the elongation of the posterior part of the
maxilla pushing forward the developing fang of a
night adder (d.a.o. = days after oviposition)
From Vonk et al. 2008
Unlike the first two groups, opisthoglyphous fangs appear to have evolved more than once, in snakes as diverse as Quill-snouted Snakes, Neck-banded Snakes, and Boomslangs. At least, that's what we used to think. Actually, it is likely that both solenoglyphous and proteroglyphous fangs evolved from opisthoglyphous fangs, as revealed by an ingenious study that used evidence from embryology and genetics to reveal the evolutionary origins of the three types of snake fangs. In a snake embryo, tubular fangs are formed by the infolding of ridges on the front and back sides of the fang, such as those that form the groove of opisthoglyphous fangs. Furthermore, front fangs develop from the rear part of the upper jaw, and are strikingly similar in their formation to rear fangs. They are pushed into the front of the mouth by disproportionate growth of the initially small part of the maxilla that is behind them. Finally, in the anterior part of the maxilla of front-fanged snakes, expression of a gene called sonic hedgehog, which is responsible among other things for the formation of teeth, is suppressed.

Relative size of the venom gland (VG) in
A: rear-fanged colubrid (Helicops leopardinus),
B: boomslang, C: homalopsid,
D: cornsnake, E: African egg-eater
SG = supralabial salivary gland
From Fry et al. 2008
Although developmental similarity is not conclusive proof of structural homology (similarity due to inheritance rather than due to other factors), these findings are consistent with the hypothesis that solenoglyphous, proteroglyphous, and at least some opisthoglyphous fangs are homologous structures. The hypothetical evolutionary trajectory was thus: some snakes evolved grooved fangs in the rear of their mouth. In a few cases (viperids, elapids, and atractaspidines), they subsequently lost the preceding teeth as what was formerly a rear fang became a tubular front fang. Other snakes retained their anterior teeth (at least some non-front-fanged colubroids), and still others developed fangs but then lost them (aglyphs such as ratsnakes). Evidence for this surprising final part comes from the formation of the maxilla and its teeth, which takes place in a single piece in pythons, but from two pieces in all fanged snakes as well as in ratsnakes, a pattern which supports a single evolutionary origin and subsequent loss of fangs. Additionally, vestigial Duvernoy's glands have been found in ratsnakes, egg-eaters, pareatid slug-eaters, and other nonvenomous aglyphs, a discovery that has led to the misleading generalization that all snakes are venomous and much subsequent misunderstanding among the non-scientific community. Toxic saliva does not a venomous animal make, as evidenced by the fact that even human saliva injected subcutaneously will produce pain and swelling.

Aglyphous

Both boas and pythons have only
aglyphous teeth, which is about
the only thing this film got right.
This word is used to describe unmodified teeth, essentially non-fangs. All snakes, even those that possess fangs of the first three types, have aglyphous teeth which they use for gripping their prey as they manipulate it during swallowing. As I just mentioned, many advanced snakes that today have only aglyphous teeth probably evolved from fanged ancestors. Several of these snakes, such as North American kingsnakes, ratsnakes, and bullsnakes, have atrophied Duvernoy's glands that lack toxin-producing serous cells. These snakes employ other sophisticated techniques, such as constriction, which is also used by more primitive snakes like boas and pythons (which did not evolve from fanged ancestors).

There are very few dangerous species of aglyphs, but one, Rhabdophis tigrinus, is becoming well-known as one of the only snakes capable of sequestering toxins from its prey for use in its own defense. This species has enlarged posterior maxillary teeth that lack grooves, so they are by definition aglyphous. However, it has relatively potent venom and has caused the deaths of several people. Among colubroids, the distinction between opisthoglyphs and aglyphs has never been entirely clear, but I'm distinguishing between them here because they are two of the four traditionally recognized types of snake teeth. Although the four types of snake teeth in this article are commonly discussed, a more accurate classification for snake teeth might be to divide them into tubular (the fangs of viperids, elapids, and atractaspidines), grooved (the rear fangs of non-front-fanged colubroids), and ungrooved (all other snake teeth).

Aglyphous (ungrooved) teeth and rear fangs of
Rhabdophis tigrinus
From Mittleman & Goris 1974
Happily for snake biologists like myself, the evolution of fangs opened the door for a massive evolutionary radiation of advanced snakes (>2800 species, or >80% of all living snake species). Although sophisticated venom delivery systems, of which fangs are just one of many integral parts, were clearly evolutionary advantageous, they have obviously also been costly at times, leading to their loss in ratsnakes, egg-eaters, and other lineages of advanced snakes. Also worth noting is that many lineages of basal snakes have got along just fine without venom, so there is not an inherent superiority of being venomous as the word "advanced" seems to imply. Rather, some have suggested that during periods of transition from forest to grassland, such as that which took place simultaneous to the dramatic colubroid radiation during the Miocene, snake taxa that were characterized by slow locomotion and constriction (boas & pythons) were supplanted by those characterized by rapid locomotion (many aglyphous colubrids) or passive immobilization (tubular- and grooved-fanged vipers, elapids, and atractaspidines that could use venom to catch their prey). Of course, both slow locomotion and constriction have subsequently been re-evolved among the colubroids, but there has been a lot of time since the Miocene.

ACKNOWLEDGMENTS

Thanks to Daniel Rosenberg (boomslang fang) and Nick Kiriazis (hognose fang) for use of their photographs.

REFERENCES

Bauchot R, editor. 2006. Snakes: A Natural History. New York, New York: Sterling Publishers. <link>

Cundall, D., (2002) Envenomation strategies, head form, and feeding ecology in vipers. In: Biology of the Vipers: 149-162. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>

Greene, H. W. (1997) Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press <link>

Fry BG, Scheib H, van der Weerd L, Young B, McNaughtan J, Ramjan SR, Vidal N, Poelmann RE, Norman JA, 2008. Evolution of an arsenal: structural and functional diversification of the venom system in the advanced snakes (Caenophidia). Mol Cell Proteomics 7:215-246 <link>

Hayes, W. K., S. S. Herbert, G. C. Rehling & J. F. Gennaro, (2002) Factors that influence venom expenditure in viperids and other snake species during predator and defensive contexts. In: Biology of the Vipers: 207-234. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>

Jackson K, 2002. How tubular venom‐conducting fangs are formed. J Morphol 252:291-297 <link>

Kardong, K. V. & T. L. Smith, (2002) Proximate factors involved in rattlesnake predatory behavior: a review. In: Biology of the Vipers: 253-266. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>

Kardong KV, 1996. Snake toxins and venoms: an evolutionary perspective. Herpetologica 52:36-46 <link>

Kuch, U., J. Müller, C. Mödden & D. Mebs (2006). Snake fangs from the Lower Miocene of Germany: evolutionary stability of perfect weapons. Naturwissenschaften 93, 84-87

LaDuc, T. J., (2002) Does a quick offense equal a quick defense? Kinematic comparisons of predatory and defensive strikes in the Western Diamond-backed Rattlesnake (Crotalus atrox). In: Biology of the Vipers: 267-278. G. W. Schuett, M. Höggren, M. E. Douglas & H. W. Greene (Eds.). Eagle Mountain Publishers, Eagle Mountain, UT <link>

Mittleman M, Goris R, 1974. Envenomation from the bite of the Japanese colubrid snake Rhabdophis tigrinus (Boie). Herpetologica 30:113-119 <link>

Pyron, R. A., F. T. Burbrink, G. R. Colli, A. N. M. de Oca, L. J. Vitt, C. A. Kuczynski & J. J. Wiens (2011). The phylogeny of advanced snakes (Colubroidea), with discovery of a new subfamily and comparison of support methods for likelihood trees. Mol. Phylogenet. Evol. 58, 329-342 <link>

Savitzky AH, 1980. The role of venom delivery strategies in snake evolution. Evolution 34:1194-1204 <link>

Shea G, Shine R, Covacevich JC, 1993. Elapidae. In: Glasby C, Ross G, Beesley P, editors. Fauna of Australia. Canberra: AGPS <link>

Vonk FJ, Admiraal JF, Jackson K, Reshef R, de Bakker MA, Vanderschoot K, van den Berge I, van Atten M, Burgerhout E, Beck A, 2008. Evolutionary origin and development of snake fangs. Nature 454:630-633 <link>

Weinstein SA, Warrell DA, White J, Keyler DE, 2011. "Venomous" Bites from Non-Venomous Snakes: A Critical Analysis of Risk and Management of "Colubrid" Snake Bites. Amsterdam: Elsevier <link>

Weinstein SA, White J, Keyler DE, Warrell DA, 2013. Non-front-fanged colubroid snakes: A current evidence-based analysis of medical significance. Toxicon. 69, 103-113 <link>

Weinstein S, White J, Westerström A, Warrell DA, 2013. Anecdote vs. substantiated fact: the problem of unverified reports in the toxinological and herpetological literature describing non-front-fanged colubroid (“colubrid”) snakebites. Herpetological Review 44:23-29.

Wüster, W., L. Peppin, C. Pook & D. Walker (2008). A nesting of vipers: Phylogeny and historical biogeography of the Viperidae (Squamata: Serpentes). Mol. Phylogenet. Evol. 49, 445-459 <link>

Young BA, Dunlap K, Koenig K, Singer M, 2004. The buccal buckle: the functional morphology of venom spitting in cobras. J Exp Biol 207:3483-3494 <link>
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50,000 Hits & Snakes from Florida

October 15, 2013, 8:31 pm
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Brown Anole (Anolis sagrei)
The purpose of my trip
This week I am in northeast Florida collecting lizards for my PhD research (don't tell anybody who still thinks I only work on snakes). This is a special place for me because it is where I started writing this blog a year and a half ago. Since that time Life is Short but Snakes are Long has received thousands of visitors: almost 100,000 if you go by the stats included with Blogger, but probably closer to 48,000 using stats from the more conservative Google Analytics, which doesn't count bots and other non-human visitors. The true number is probably somewhere in the middle. With many thanks to Alvaro Permartin and Estefania Carrillo, all posts are available in English and Spanish (the links to the Spanish versions are at the top of each post), and I am working on converting the format of the Spanish pages from PDF to HTML to more closely resemble the English pages. Readers from the USA make up the majority of visitors, but the UK, Canada, Australia, and India are also well-represented, and readers from 177 countries or territories have visited. 

Map of visits to this blog
I am proud to have been able to disseminate knowledge about snakes to so many people. The first post on snake sheds is still the most popular, garnering between 44 and 100 hits a day and appearing in the top 10 hits for Google searches for 'snake shed' and 'snake sheds'. Its popularity prompted me to write another article that was less storytelling and more detail about the processes used in snake shed identification. As proof positive that it works, last week I received images of a snake shed from Jean in Lawrence, Kansas, who wrote:

The first photo
I happened across your blog while searching for a way to identify a snake species by it's shedded skin.

We found this [snake shed] in our barn near Lawrence Kansas. I had this extreme fear of snakes so I became proficient in identifying them, if I see them. We have only seen 3 types of venomous snakes in our area, the timber rattler, the western massasauga, and the osage copperhead. Unfortunately, I find that I am truly inept at identifying them by their skins.

We have seen more poisonous snakes this year than usual and we found this skin inside our barn. It very easily could have been trapped inside as we close it up every other evening. We primarily use the barn for storage and workshop. Hopefully, we have allowed plenty of opportunity for the snake to escape.

I mainly want to know if you can help me to identify whether this is a poisonous snake. After reading your blog I am concerned is that it is possibly a copperhead and that it could be hiding. There are numerous places for a creature to stay hidden in our 70 ft barn and I fear that I will open a bin or cabinet and find it, dead or alive.

We love our wildlife and try to be protective and careful, but it seems we have failed at this lately as we recently had to scare an endangered skink out of the barn.

I would appreciate your assistance in possibly identifying this snake. I don't think we have the tail end of the skin. We do have the fairly intact head portion of the skin and can send more pics if needed.

Your blog is very informative and I learned a great deal from it. I thank you in advance for your assistance.

Although the first photo wasn't detailed enough, she was able to find the tail and I was able to help her identify it as a harmless ratsnake, after which she wrote:


The second photo,
showing divided subcaudals
Thank you so much! I checked your blog to take a double look at your pics there and was still unsure, so thank you so much! We did see a few rat snakes earlier this year so my guess is you are spot on!

It is still scary that we didn't see it! We live in a rural area very near to public hunting and fishing but don't have a lot of traffic. It makes my blood boil at the number of snakes we see dead on the SIDES of the roads!

Please keep up the great work! Yours was the first site when I googled snake skin id and by far the most informative i found! I learned so much by reading your blog and I really feel that people need more education about snakes!

Identifying snake sheds has been a new challenge for me. I probably wouldn't have gotten so much practice at it if I hadn't started this blog. I am working on a lot of new content, but I particularly want to develop content that people will find useful and interesting. With that in mind, here are a couple upcoming articles that I've planned:

  • Basics of snakebite
  • Venomous bites from "non-venomous" snakes
  • Common urban snakes
  • Snake predators
  • Invasive snakes
  • Some personal stories about how I became interested in herpetology
  • Several taxon-specific posts
I'm open to suggestions about how to prioritize these and I'm especially open to ideas from readers about new posts that aren't on this list. Some of the best ones I've written so far are ones people have suggested to me. I'm also open to hosting guest posts if there are any interested guest authors out there. Feel free to leave a comment or to contact me by email.

Cornsnake from the island
I also wanted to share a couple of stories from this week. Yesterday we found a young Cornsnake on one of our islands when one of us chased a lizard into the tree hollow where it was hiding. That snake had eaten one of the Brown Anoles in our study, a large male that we marked back in 2011. Young cornsnakes are particularly fond of lizards and ambush them from hiding spots under bark and within decaying trees. My former student David Delaney, now in the Warner lab at UAB, will be conducting research on the effects of cornsnake predation on anole sleeping site selection. I thought this would be the coolest find of the whole trip, but today some folks alerted us to the presence of an Eastern Diamondback Rattlesnake on a public beach right near where we were collecting mainland lizards for David & Dan's lab experiments. This snake was in the surf, which was really foamy due to the wind. The lady who found it said she almost stepped on it. Usually when someone tells you they saw a rattlesnake nearby it's either not a rattlesnake or not there or both, but this time it was for real! I have read about EDBs entering the ocean occasionally, but apparently it is fairly rare. My friend Kerry Nelson, who worked as a naturalist on Little St. Simons Island in Georgia for almost two years and saw diamondbacks in the sand dunes daily, said to me that he never saw one in the surf.

Me with Diamondback
ACKNOWLEDGMENTS

Thanks to Hans Hillewaert, Dan Warner, and Jean Ostrander for their photos and to Jean Ostrander for allowing me to reprint her email.
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How snakes see through closed eyes

November 1, 2013, 7:49 am
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Early American symbols depicting rattlesnakes:

(top) Rattlesnake on the $20 bill issued in 1778 by Georgia.
The Latin motto (Nemo me impune lacesset) means,
"No one will provoke me with impunity."

(middle) Benjamin Franklin's "Join or Die" cartoon,
first published in the Pennsylvania Gazette in 1754.
Franklin advocated a rattlesnake as the national symbol
by writing: "...her eye excelled in brightness...she has no
eye-lids. She may therefore be esteemed
an emblem of vigilance."

(bottom) The Gadsden flag, used during
the American Revolution

Normally when someone asks me how to tell the difference between a snake and a legless lizard, I tell them to look at the eyes. Lizards have eyelids whereas snakes do not. Whenever I say this I am lying, although really I am just oversimplifying for the sake of clarity. Most lizards have obvious movable eyelids and so can blink like we do. Snakes, by contrast, seem not to have eyelids. They are ever-staring, ever-vigilant. Ben Franklin esteemed the rattlesnake as a symbol of vigilance because its eyes were always open.

Snakes' eyes are closed all the time. Rather than having movable eyelids, snakes have a single, fused, clear layer of skin over their eye, called a spectacle or brille (German for "glasses"), which protects the eye. A snake's skin is covered in scales, and the outer part of the spectacle is indeed a scale. The deeper layers of the spectacle are formed, during development, from the same embryonic tissue that in other animals forms the eyelid. The spectacle is not attached to the snake's eye in any way, so the eye can move freely behind it, although its movement is limited. This limited movement is because snakes are probably descended from fossorial lizard ancestors that lived underground and had degenerate eyes, much like today's amphisbaenians, although fossil evidence for this hypothesis is scant (as are snake fossils in general).



Eye of an Eastern Ribbonsnake (Thamnophis sauritus)
during the phase prior to shedding when fluid
has built up between the old and new spectacles
Unlike other animals' eyelids, snakes' spectacles are transparent, like a window in their skin, allowing them to see out through their always-closed eyelids. Just before a snake sheds its skin, a layer of fluid builds up between the new inner skin and the old outer layer, clouding the spectacle and causing the other scales to have a faded, milky appearance. This period usually lasts a few days, during which snakes have difficulty seeing and usually will not eat. People who keep snakes as pets have observed that they may become particularly ornery during this period, perhaps as a result of not being able to see clearly.

The horizontal, key-shaped pupil
of Ahaetulla prasina
Another obstacle to snake vision that has been long known but little studied is that snakes' spectacles are vascularized, meaning that they have blood vessels running through them. It is very unusual for tetrapods to have blood vessels in a place that might interrupt their field of vision. First noticed in 1852, these vessels are small but symmetrically distributed across the optically transmissive region of the eye in most species, although the arrangement is radial in basal snakes, acrochordids, and vipers but vertical in colubrids and elapids. In one visually-oriented species, the Asian vine snake (Ahaetulla nasuta), these blood vessels are less dense in the region of the field of vision known as the fovea, where the maximum sharpness is achieved. Most snakes don't have foveas, suggesting that the unusual arrangement of blood vessels in the eyes of Ahaetulla is an adaptation to minimize visual disturbance in this region of highest visual acuity.

Until recently, no one had considered whether movement of blood into and out of the spectacle blood vessels might aid snakes in being able to see. In an article published this week in The Journal of Experimental Biology, Kevin van Doorn and Jacob Sivak of the University of Waterloo in Ontario presented the first evidence that snakes are able to do this. When van Doorn was investigating the mechanisms snakes' eyes use to focus, he noticed the blood vessels in the spectacle, which led him to look more closely at their function. He found that coachwhips, another highly visual species, were able to reduce blood flow to the spectacle in the presence of a potential threat. At rest and undisturbed, newly oxygenated blood flowed into the spectacle blood vessels of the coachwhips for about a minute at a time, interspersed with approximately two minute periods during which no flow took place. When an experimenter walked into the room to perform some routine tasks, spectacle blood flow was almost completely cut off. What little flow there was during this period occurred in short spurts of around 30 seconds each, about half the length of the flow period in undisturbed coachwhips. When the experimenter left the room, the pattern of blood flow in the snakes' eyes returned to normal almost immediately.

Figure from van Doorn & Sivak 2013 showing blood vessels in the spectacle of a Coachwhip (Masticophis flagellum). (A) Image taken during the renewal phase of the integument when the spectacle becomes cloudy. The vessels are most apparent in the region that overlays the iris–pupil boundary because of their higher contrast with the background in this region. (B) The spectacle under retro-illumination, showing the vessels in the illuminated anterior portion of the pupil on the right side. The vessels are dorso-ventrally arranged as is typical for colubrid snakes. Debris and scratches are visible on the spectacle scale (particularly the left side), attesting to its protective role.
Shed skin of a Cornsnake (Pantherophis guttatus)
showing the shed spectacles
Furthermore, van Doorn & Sivak found that when snakes were handled they cut off blood flow to the spectacle completely, probably as part of a sympathetic nervous response. In contrast, blood flow to the eye was continuous and uninterrupted, even during handing, in shedding snakes. You can see a video of blood flow in the spectacle of a shedding corn snake here. Although no experimental evidence has been gathered that filled blood vessels in the spectacle reduce a snake's ability to see, it seems likely given that the blood vessels themselves are quite difficult to see when they are not filled with blood. Snakes actually have remarkably good color vision, better than that of rats and on par with the visual acuity of a cat. Because they move their eyes so little compared to humans, they might be less likely to notice the interruption to their visual field by these blood vessels.

Geckos and some other lizards also have spectacles. A few other species of tetrapods have blood vessels in their optical path, including manatees, armadillos, and some blind salamanders, none of which are renowned for their visual prowess. Little is known about the images these vessels might project onto the vision of these animals, but because they are part of the cornea and so move about with the eye rather than remain stationary relative to it, their area of occlusion would appear to remain stationary to the animal. This is not true for animals with nictitating membranes (diving animals such as penguins or crocodilians) or those with spectacles, both of which have the potential to interrupt the animal's vision. We don't know yet how crocodilians and geckos deal with this issue, but as with so many other features of their lives, snakes have evolved an ingenious and potentially unique solution to a vexing problem, allowing them to remain vigilant as well as keep their eyes protected. Snakes have guarded the Golden Fleece in the Greek tale of the hero Jason and his band of Argonauts, a treasure chamber beneath an ancient city in Rudyard Kipling’s The Jungle Book, and various other treasures in Hindu, Inca, and Basque mythology, all with their eyes closed.

ACKNOWLEDGMENTS

Thanks to Hans Breuer and Kwok Wai for their photographs of Ahaetulla prasina.

Correction: I originally said that the fovea work was done on Ahaetulla prasina, but it was actually Ahaetulla nasuta. Both species have horizontal pupils so it is likely that the reduction in blood vessels is found in both.

REFERENCES

Baker, RA, TJ Gawne, MS Loop, and S Pullman (2007) Visual acuity of the midland banded water snake estimated from evoked telencephalic potentials. J. Comp. Physiol. A 193, 865-870 <link>

Crump, ML (in press) Amphibians, Reptiles, and Humans: Cultural Perceptions and Conservation Consequences. University of Chicago Press.

Foureaux, G, MI Egami, C Jared, MM Antoniazzi, RC Gutierre, and RL Smith. (2010) Rudimentary eyes of squamate fossorial reptiles (Amphisbaenia and Serpentes). Anat. Rec. (Hoboken) 293, 351-357 <link>

Franklin, B (1775) The rattlesnake as a symbol of America. Pennsylvania Journal. <link>

Lüdicke M, 1969. Die kapillarnetze der brille, der iris, des glaskörpers und der chorioidea des auges vom baumschnüffler Ahaetulla nasuta Lacepede 1789 (Serpentes, Colubridae). Zoomorphology 64:373-390.

Mead, AW (1976) Vascularity in the reptilian spectacle. Invest. Opthalmol. Vis. Sci.15, 587-591 <link>

Neher, EM (1935) The origin of the brille in Crotalus confluentus lutosus (Great Basin rattlesnake). Trans. Am. Ophthalmol. Soc. 33, 533-545 <link>

Quekett, J. (1852). Observations on the vascularity of the capsule of the crystalline lens, especially that of certain reptilia. Trans. Microsc. Soc. Lond. 3, 9-13. doi:10.1111/j.1365-2818.1852.tb06020.x

van Doorn, K. and Sivak, J. G. (2013). Blood flow dynamics in the snake spectacle. J. Exp. Biol. 216, 4190-4195 <link>
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Snakes that polish their scales, and why they do it

November 10, 2012, 11:15 am
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Psammophis schokari eating a lizard, Phrynocephalus
mystaceus, in Kazakhstan
I really like these snakes, and they have about them a pretty interesting mystery. In the tribe Psammophiini (in family Lamprophiidae), there are at least 50 species of snake in 8 genera native to Africa, the Mediterranean, the Middle East, and central Asia. They are united by several unusual synapomorphies, the most unique of which is the presence of a morphological feature called the external narial valve. This structure, located in the loreal region between the eye and the nostril, is the outlet of a special nasal gland that secretes fluid containing long-chain fatty acids. The function of this secretion is enigmatic. Some experiments show that it can serve to retard evaporative water loss, and some evidence suggests that some of these molecules could be pheromones used in marking territories. Territoriality is only slightly less non-existent among snakes than herbivory, but according to some it is apparently present among certain psammophines, few of which have been well-studied in the wild. Aside from a very interesting study suggesting that releasing small mammals from competition with large herbivores can indirectly increase the abundance of their snake predators (including Psammophis mossambicus), we don't know much about their ecology, but careful observations have revealed a little about the lives of these intriguing snakes.

Subadult Montpellier snake, Malpolon monspessulanus
The external narial valve was described in 1956 by renowned Russian herpetologist Ilya Darevsky, the second person ever to earn a PhD in the Soviet Union and the discoverer of parthenogenesis and polyploidy in reptiles. Darevsky described the gland from a specimen of the Montpellier snake (Malpolon monspessulanus), and such glands have now been reported from all eight genera in the Psammophini. In addition to the gland, psammophines also share peculiar hemipene morphology - that is, the male reproductive organs are unusually thin and smooth for an advanced snake, most of which possess thick, spiny hemipenes that enable prolonged copulation. Sexual dimorphism is also quite pronounced in many of these snakes, although not of tail length (typically, the tails of male snakes are longer and thicker than those of females). For example, male M. monspessulanus are stout, uniformly colored, and up to 2.3 m long, whereas females are slender, spotted, and reach only 1.4 meters.

Beginning in 1898, the earliest observations of these snakes mention their peculiar behavior. Psammophines press the outlet of their narial valve to their skin and thoroughly apply a coating of colorless, fast-drying valve secretion all over their body. Watch this Malpolon insignitus to get an idea, because it's hard to describe.




This behavior has been variously called self-rubbing, self-polishing, or  grooming, and seems to be present in all species of psammophine observed. Several keepers in Europe have made extensive efforts to acquire and videotape species of psammophines, and self-rubbing has now been documented in seven of the eight genera. More intriguing, conspecific psammophines housed together occasionally rub one another, presumably anointing the other snake with secretion from their narial valve. What could this mean?


Psammophis leightoni from Namibia
Several hypotheses have been put forth to explain this unique and intriguing behavior. To date, none have been sufficiently tested to unequivocality, nor are they mutually exclusive. Prior to the 1970s, the prevailing thought was that, since psammophines generally inhabit arid regions, the gland might aid in salt excretion, evaporative cooling, or water retention. In 1978, William Dunson and colleagues published their work on the histology of the gland, and concluded that it did not contain the specialized cytological features associated with salt secretion in the salt glands of reptiles such as sea snakes and marine iguanas. Dunson also characterized the chemical composition of the secretion for the first time, and suggested that the long-chain fatty acids he found might help retard water loss through the skin.


Dunson tested five Malpolon to see if their dermal water loss was unusually low, and indeed it was, approximately ten times lower than that of Kingsnakes (Lampropeltis getula), although water loss rate varied depending on where in the shedding cycle the snakes were. Malpolon also lost proportionally more water via the mouth and cloaca (and less via the skin) than did other reptiles. Dunson also kept Malpolon without giving them access to water, and they did not lose weight, indicating that they were capable of obtaining all the water they needed from their prey. In another experiment, he showed that dehydrated Malpolon did not secrete salt from their narial valve. He made the interesting observation that several frog species of the genus Phyllomedusa decrease their dermal water loss by wiping lipid secretions from skin glands over the surface of their skin:




Could psammophids be accomplishing the same thing with their narial valve secretions? Dunson did not test whether snakes that had just applied the secretion lost less water than those that had not. The snakes polish themselves frequently, especially after ecdyisis and feeding, so water loss rate could be tracked over time. 

Other mysterious pits have been described from the head scales of psammophines: parietal pits on the top of the head and infralabial pits on the lower jaw, both of which seem to be sporadically occurring. Series of shed skins from the very same snake sometimes show these features and sometimes do not. Because histology is lacking for these features, it is difficult to say what they might represent.


Dipsina multimaculata
Because of the remote areas inhabited by many of these snakes, most studies to date are insufficiently replicated to permit concrete conclusions about the function of the polishing behavior. Furthermore, determining the sex of living psammophines is quite difficult on account of their small hemipenes, so behavioral studies are often hampered by inadequate knowledge of the sex of the animals involved. Observations of captive psammophines suggest that these snakes have complex social behaviors, not the least of which is their tendency to polish one anothers' scales. Could this behavior represent mate guarding? A nuptial gift from males to females of fatty acids to help them avoid water loss during pregnancy? Do these snakes mark their territories? Only replicated, scientific studies will tell; until then, competing hypotheses will continue to wax on and wax off.


ACKNOWLEDGMENTS

Thanks to Heather Heinz for drawing my attention to this fascinating system, to Jane Bugaeva for translating Darevsky's 1956 article from Russian, and to photographers Bernard Dupont, Altyn Emel, Michael & Patricia Fogden, and Jeremy Holden, and videographer Ton Steehouder.

REFERENCES

Microdermatoglypic SEM photograph of Dipsina scale.
The lipid layer covering the scale is visible.
From de Pury 2010
Darevsky IS (1956) O stroyenni i funktsionirovani nosovoy zhelezy u yashtsheritsnoy zmei Malpolon monspessulanus Herm. (Reptilia, Serpentes). [On the structure and function of the nasal gland in the lizard snake Malpolon monspessulanus Herm. (Reptilia, Serpentes)] Zoologicheskij Zhurnal-Moskva 35:312-314

Dunson WA, Dunson MK, Keith AD (1978) The nasal gland of the Montpellier snake Malpolon monspessulanus: fine structure, secretion composition, and a possible role in reduction of dermal water loss. Journal of Experimental Zoology 203:461-473

de Grijs P (1898) Beobachtungen an reptilien in der gefangenschaff. Zoologischer Garten 39:233-247

de Haan CC, Aymerich M (2012) Des comportements frotteur et marqueur, pour la chasse et la vie sociale. In: Aymerich M (ed) A la Découverte de la Faune du Maroc Oriental

de Haan CC, A Cluchier (2006). Chemical marking behaviour in the psammophiine snakes Malpolon monspessulanus and Psammophis phillipsi. Proceedings of the 13th Congress of the Societas Europaea Herpetologica, 211-212. <link>

Mimophis mahfalensis killing a chameleon in Madagascar
de Haan CC (2003) Extrabuccal infralabial secretion outlets in Dromophis, Mimophis and Psammophis species (Serpentes, Colubridae, Psammophiini). A probable substitute for ‘self-rubbing’ and cloacal scent gland functions, and a cue for a taxonomic account. Comptes Rendus Biologies 326:275-286. <link>

de Pury S (2010) Analysis of the Rubbing Behaviour of Psammophiids: A Methodological Approach. PhD dissertation, Rheinischen Friedrich-Wilhelms-Universität Bonn, Bonn, Switzerland.

McCauley, D. J., Keesing, F., Young, T. P., Allan, B. F. & Pringle, R. M. 2006: Indirect effects of large herbivores on snakes in an African savanna. Ecology 87, 2657-2663. <link>
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Identifying snake sheds, part III

November 18, 2012, 7:43 am
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I noticed that a huge proportion of the hits on this site are for the posts about identifying snake sheds (parts I and II), which I expect is a result of people searching for a key or guide to use to ID a snake shed that they have seen or found. Even though there is some useful information in those other posts, they are written more like detective stories with a particular conclusion in mind, and they certainly aren't comprehensive.

Here, however, I've attempted to put together a more complete how-to guide on how to ID sheds of snakes found in the United States and Canada. One excellent free reference on this subject is an electronic pamphlet by Brian Gray called A Guide to the Reptiles of Erie County, Pennsylvania. Even if you don't live in Erie County, Brian's section on shed snake skins is a very useful guide to many of the common species found in the eastern United States, because it contains many excellent, high-resolution images of the scale characters, and it is organized as a dichotomous key: a series of questions, each with two choices, that inevitably leads to an identification (it's sort of like a choose-your-own-adventure book). Brian's more comprehensive book, The Serpent's Cast, is also an excellent resource, containing images of shed skins that have been painstakingly prepared for viewing the details of the scales necessary for identification to species. Although shed skins that you are trying to identify won't always be that cleanly preserved, often many of the identifying features are still visible.

From Cardwell 2011; viper (top) and colubrid (bottom)
The first thing that many readers will want to know will be whether or not the snake whose shed skin they have found is a venomous species. This distinction corresponds nicely with determining what family the snake is in. In most of North America, there are two families: Viperidae (vipers, which are venomous) and Colubridae (colubrids, which are not1). The easiest way to distinguish these two families by their shed skins is to locate the sub-caudal scales (the scales under the tail). Colubrids have a double row of scales under the tail, whereas vipers have a single row. This is a pretty invariant character, especially near the anterior part of the tail, and it can help you tell the family of the snake whose shed you've found every time. Coral snakes, which are in the family Elapidae, also have a double row of scales under the tail, but if you think you have found a coral snake shed, post a pic because that's an amazingly lucky find. More about these, and a few other options, later. First, colubrids:

Divided anal scale
Single anal scale
Once you have figured out the family, a second pair of characteristics can help you narrow down which genus of colubrid you might have. These are 1) the texture (smooth or keeled) of the dorsal scales (these are the relatively small scales that cover the snake's entire back and sides) and 2) the condition (single or divided) of the anal scale or anal plate (the scale covering the cloaca). Keeled dorsal scales have a ridge running down the center, whereas smooth dorsal scales have no ridge, like so:

Smooth (left) and keeled (right) dorsal scales
Using these characteristics in tandem should allow you to divide the colubrids in to four groups: single/smooth, divided/smooth, single/keeled, and divided/keeled. These are not taxonomic groups (that is, not all single/smooth snakes are each others' closest relatives), but they are useful for distinguishing genera of colubrids when all you have to go on is the shed skin. All North American vipers have keeled scales and a single anal scale, so these characters are less useful for distinguishing them, but more on these later. Most of the species of North American snake are colubrids (about 80%, or 105 of our 131 species). Here is a quick guide to the colubrids of the US and Canada, by dorsal and anal scale characteristics:


A few genera are split among multiple categories: Gyalopion because G. quadrangulare has a single anal scale whereas G. canum has a divided anal scale, and Opheodrys and Virginia because one species of each has keeled scales and the other has smooth (these are helpfully called Rough and Smooth Green and Earth Snakes, respectively). It's also worth noting that anal scales of Farancia are pretty variable, although your chances of finding a Farancia shed are slim (but see part I).

As you can see, we are using the process of elimination to narrow down the possible candidate species for your shed. A quick look at the range maps in a regional fieldguide will allow you to cross off about half the genera on the above list, depending on where you live, probably leaving you with 2-6 possibilities. The overall size of the shed can also be of help, although keep in mind that large snakes are born small and that snake sheds stretch somewhat as they are removed. Still, many of the snakes on the above chart reach adult sizes of only 12-24", so they could potentially be eliminated on the basis of size. Width of the ventral scales can help too, because it gives you an idea of body shape, and this does not change as much during the shedding process. However, at this point, the most useful thing to do next is to look at another scale meristic. One that can help you distinguish among the several genera within each group requires counting the dorsal scale rows. Dorsal scales are arranged in rows, the number of which can be counted from left to right, like so:

Three equally good ways to count dorsal scale rows (in C, scale 1 not shown). Modified from K. Jackson (2013)
You'll want to start with the first dorsal in contact with a ventral on one side and proceed over the back and down the other side so that the last scale counted is the dorsal scale in contact with a ventral on the other side of the snake. Although the conventional way (A) is for this to be the same ventral scale as the one your first dorsal scale row was in contact with (that is, count in a ‘V’ shape, as depicted above, so that you are counting all the scales associated developmentally with a single pair of ribs), you should get the same result even if your 'V' is asymmetrical (B), or even if you count in a straight line (C), which can be easier since you don't have to decide where to change direction on the 'V'. Often it doesn't matter, although it's worth noting that in some snakes the number of dorsal scale rows varies along the length of the snake. The best way to guard against this is to count a row in the middle of the body, which is the number meant if only one is given in most keys. More often, you will see numbers of dorsal scale rows given in the format “15-17-15”, indicating the number of dorsal scale rows at three places on the body (in order): the neck, midbody, and a bit (about one head length) before the cloaca.

In North America, you should almost always get odd numbers, and although these numbers can sometimes be fairly variable, combining them with decisions you made above based on the subcaudals, anal scale, dorsal texture, body size, and range should allow you to decide on a genus in almost 100% of cases. Here is a list of the dorsal scale formula ranges for the North American colubrids (remember, it's neck, midbody, and before the cloaca). Where ranges are given in parentheses, species within that genus have differing scale formulas. Where ranges are given without parentheses, there is regional or other variation within one or more of the species in that genus. In a few cases, only the scale row counts at midbody are given.

Knowledge of the number, shape, and relative size of the head scales is usually necessary to distinguish among species within a genus (for example, to tell a Scarlet Kingsnake from a Mole Kingsnake), and unfortunately many sheds are missing their heads or the heads are in poor condition. Other clues can be obtained from pattern, which is often visible in good light, and from counting the total number of subcaudal or ventral scales (impossible if you only have a partial shed). If you have taken your shed to genus and want to send me pictures of the head for help identifying it to species, feel free. I would recommend using your digital camera's macro setting (almost all cameras have one, the symbol is a little flower) to photograph snake sheds. You can also find details of the head scalation of all species of North American snakes in the book Snakes of the United States and Canada by Ernst & Ernst, and much of this information is available online as well. It's often helpful to keep the shed in a Ziploc bag for later reference. I like to write on the bag with a Sharpie the date, location, and tentative ID of the snake.

Non-colubrids

As I mentioned above, all North American vipers have single subcaudals, keeled dorsal scales, and a single anal scale, so these characters are less useful for distinguishing them from one another. However, there are only three genera: Agkistrodon (Copperheads and Cottonmouths), which have no rattles, and two genera of rattlesnakes, Crotalus (which have small scales on the tops of their heads) and Sistrurus (which have large scales on their heads). Telling the different species of Crotalus by their sheds could be tricky, but unless you live in Arizona, there are usually only one or two options in any given location in the US. Size and pattern could also be helpful. Feel free to share pictures (remember to use macro). Copperhead and Cottonmouth sheds can be hard to distinguish, but range, size, and habitat can help, as well as the presence or absence of a loreal scale (the scale on the face between but not in contact with either the eye or the nostril), which Copperheads have and Cottonmouths do not.

Micrurus fulvius
If you live in certain parts of the US, there are a few other snakes that aren't colubrids or viperids whose sheds you might find. One familiar group is the elapids, represented in North America by the Coral Snakes. One species is found in Arizona and New Mexico, and the other in the southeastern coastal plain from Texas to North Carolina. I have never seen a Coral Snake shed, but I would imagine that the highly contrasting, distinctly banded pattern would be easily visible. However, these can also be distinguished by their scale characteristics: Micrurus fulvius has smooth dorsal scales in 15 rows and a divided anal plate, and Micruroides euryxanthus has smooth dorsal scales in a 17-15-15 pattern with a divided anal plate. The other US elapid, the Yellow-bellied Sea Snake (Pelamis platurus, found in the Pacific Ocean off southern California) sheds at sea, so unless you are in very unusual circumstances the sheds will not be found. They have smooth scales with a 39-47, 44-67, 33-46 row formula and a divided anal plate.

Lichanura trivirgata
If you live in southern California or the intermountain west, there are two species of temperate boids, the Rubber (Charina) and Rosy (Lichanura) Boas, whose sheds you could find. Boa sheds are very different from those of other snakes. Boas have small, round dorsal scales that are very numerous - Charina and Lichanura have 32-53 and 33-49 dorsal scale rows, respectively, so you should be able to tell a boa shed by the small size and number of dorsal scales. Rubber Boas have blunt tails and specialized head scales, whereas Rosy Boas have long tails and unspecialized head scales, and their ranges do not overlap. If you live in southern Florida, you might find sheds of Boa Constrictors or Burmese Pythons, which you should be able to tell by their huge size, or any number of other exotic snakes (good luck with those).

Rena humilis
Finally, the southwestern US is home to several species of scolecophidian blindsnakes in the genera Rena and Leptotyphlops. These are tiny and have undifferentiated body scales, meaning that all scale rows around the entire body (including the underside) are the same width. They are iridescent and extremely difficult to count, which has given rise to one of my all-time favorite quotes from a scientific paper: "We castigate the ancient lineage that begat Liotyphlops, for it is obviously the worst designed snake from which to obtain systematic data" (Dixon & Kofron 1983). An additional species, Ramphotyphlops braminus, is introduced in Florida, Louisiana, and Hawaii, as well as in many other locations around the world (it's parthenogenetic and so a really good invader because it only takes one!). Blindsnakes shed their skins in a series of rings rather than in a single piece, and they are so small that any sheds found would be unlikely to belong to any other kind of snake and so fairly easy to identify.

Feel free to comment or email with questions or photographs. Happy herping!


1 I am making a distinction between North American snakes that are dangerously venomous to humans (vipers & coralsnakes) and those that aren't (colubrids). Although some species of colubrid snake possess deadly venom, such as boomslangs and twigsnakes, these are not native to North America. Other colubrids, including some North American species such as Hog-nosed Snakes (Heterodon), are venomous in the sense that their Duvernoy's gland secretions are toxic to their prey, but are harmless or nearly so to humans. For a very thorough discussion of this issue, check out the book "Venomous" Bites from Non-Venomous Snakes.
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ACKNOWLEDGMENTS

Thanks to Brian Gray, Jack Goldfarb, and JD Willson for their excellent photographs.

REFERENCES

Cardwell MD (2011) Recognizing Dangerous Snakes in the United States and Canada: A Novel 3-Step Identification Method. Wilderness & Environmental Medicine 22:304-308. <link>

Dixon JR, Kofron CP (1983) The Central and South American anomalepid snakes of the genus Liotyphlops. Amphibia-Reptilia 4:2-4. <link>

Ernst CH, Ernst EM (2003) Snakes of the United States and Canada. Smithsonian Institution Press, Washington D.C. <link>

Gray BS (2011) A Guide to the Reptiles of Erie County, Pennsylvania. Natural History Museum at the Tom Ridge Environmental Center, Erie, Pennsylvania. <link>

Weinstein SA, Warrell DA, White J, Keyler DE (2011) "Venomous" Bites from Non-Venomous Snakes: A Critical Analysis of Risk and Management of "Colubrid" Snake Bites. Elsevier, Amsterdam. <link>
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