Gaboon Viper

The Gaboon viper is a large, highly venomous snake of the rainforests and savannas of sub-Saharan Africa and the largest member of the genus Bitis. It is heavy and stout, with a large triangular head and a pattern of pale blotches and dark hourglass markings that provides strong camouflage among dead leaves. It is mainly nocturnal and hunts by ambush, lying motionless until prey passes, and it eats amphibians, birds and mammals up to the size of a fully grown rabbit. Despite its reputation for being slow-moving and placid, it is one of the fastest-striking snakes in the world.

About the Gaboon viper

The Gaboon viper is a large, heavy-bodied, highly venomous viper of the rainforests and nearby woodlands of sub-Saharan Africa. It is the largest member of the African adder genus Bitis, related to the puff adder, and has the longest fangs and highest venom yield of any snake.

Its scientific name is Bitis gabonica, and it also goes by Gaboon adder, butterfly adder, forest puff adder, whisper and swampjack. "Gaboon" refers to the Gabon estuary where Libreville now stands. Adults typically reach 125 to 155 cm (4.1 to 5.1 ft) in total length, though some sources give a smaller typical range of 80 to 130 cm (31 to 51 in).

What sets it apart is bulk. It is the heaviest venomous snake in Africa and one of the heaviest in the world, alongside the king cobra and the eastern diamondback rattlesnake. One 174 cm (69 in) female had a head 12 cm (4.7 in) wide, a body 37 cm (15 in) around and a weight of 8.5 kg (19 lb). A 1.8 m (5.9 ft) snake caught in 1973 weighed 11.3 kg (25 lb) on an empty stomach.

The head is large and triangular, sitting on a neck only about a third as wide, with a pair of tiny "horns" between the raised nostrils. The eyes are large, set well forward and unusually mobile. When one eye looks forward, the other looks back, and the eyes often flick rapidly back and forth. Males have longer tails than females, about 12% of total length against 6%.

The color pattern looks gaudy in the open: pale, roughly rectangular blotches down the middle of the back, separated by dark, yellow-edged hourglass shapes, with fawn or brown diamond shapes on the flanks. The cream head has a thin dark center line and a blue-black triangle behind and below each eye. Among dead leaves on a forest floor, though, the pattern works as near-perfect camouflage, so effective that fully exposed snakes are easy to overlook even in a leaf-lined enclosure.

Behavior and diet

Gaboon vipers are mainly nocturnal and solitary, most active around sunset. They hunt mostly by ambush, lying motionless among leaf litter for long periods until prey passes, though they sometimes hunt actively in the first six hours of the night. They move slowly, mostly in a straight line by "walking" on their belly scales.

Their reputation is for being placid. They rarely hiss or bite, even when handled, and are unlikely to strike unless badly provoked. When threatened they may give a deep, steady, rhythmic hiss, flattening the head slightly with each breath. When they do strike, they are among the fastest-striking snakes in the world.

Adults are big enough to swallow fully grown rabbits. They strike from any angle, can reposition their fangs if they miss, and then hang on rather than releasing the prey to die, unlike most vipers. Prey includes rodents such as mice and rats, hares and rabbits, birds such as doves, guineafowl and francolins, and frogs and toads. More surprising meals have included tree monkeys, Gambian pouched rats, brush-tailed porcupines and even small royal antelope.

During the breeding season males wrestle. Two males rise up with their necks intertwined and push against each other, sometimes squeezing so tightly that their scales stand out, until one forces the other's head to the ground. Mating takes place in the rainy season, and gestation lasts about seven months. The young are born live, typically 30 to 40 at a time and as many as 50 to 60, already about 30 cm (12 in) long with the adult pattern. There is no parental care.

Range and habitat

The Gaboon viper is found across much of sub-Saharan Africa. Its range includes Guinea, Ghana, Togo, Nigeria, Cameroon, Gabon, both Congos, northern Angola, the Central African Republic, South Sudan, Uganda, Kenya, eastern Tanzania, Zambia, Malawi, eastern Zimbabwe, Mozambique and northeastern KwaZulu-Natal in South Africa. Some lists also include Sierra Leone, Senegal, Ivory Coast and Liberia.

It lives mainly in rainforest and nearby woodland at low altitudes, sometimes up to 1,500 m (4,900 ft) and reportedly as high as 2,100 m (6,900 ft). It does well in cleared forest turned to cacao or coffee plantations, and turns up in thickets, cashew plantations, farmland near forest, swamps and along roads at night. In Zimbabwe it lives only along the wet, forested eastern escarpment.

Gaboon viper vs puff adder

The puff adder (Bitis arietans) is the Gaboon viper's close relative. The Gaboon viper generally lives in environments that parallel the puff adder's, but the puff adder normally keeps to more open country.

The western population once treated as a subspecies of the Gaboon viper is now often recognized as a separate species, Bitis rhinoceros. Genetic work found it as different from the Gaboon viper as both are from the rhinoceros viper. The record 205 cm (81 in) Sierra Leone specimen belongs to that western form.

Conservation status

The Gaboon viper is listed as Vulnerable on the IUCN Red List in a 2021 assessment. No specific threats are given for that listing. An older account described the species as not threatened and noted that it has no known natural predators.

Bites on people are extremely rare, because the snake is seldom aggressive and lives mostly in rainforest. Most victims are people who step on one by accident, and not every such encounter ends in a bite. When a bite does happen, it is a serious medical emergency. The venom is cytotoxic and cardiotoxic, and the enormous venom glands deliver the second-largest venom quantity of any snake, with reported yields of 200 to 1,000 mg of dried venom per milking. Published estimates of a fatal human dose range from about 14 to 100 mg. Bites cause rapid swelling, intense pain, shock and blistering, and can lead to amputation or death. Antivenom is needed as soon as possible.