Africa's Giant Gaboon Vipers

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.

ACKNOWLEDGMENTS

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

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