Gaboon viper

Identification

The Gaboon viper is a large, very heavy-bodied viper with a broad, triangular, pale head^9,10, and a pair of horn-like scales on the tip of its snout¹⁰. Its back has a geometric pattern of pale buff or yellowish rectangles linked by darker hourglass shapes on a brown or purplish background, with dark triangles along the sides, which hides it well among fallen leaves¹⁰. A thin dark line runs down the middle of the head¹⁰. It has two dark triangles below each eye, while the closely related western Gaboon viper has only one^1,6.

Adults average about 1 m long, and the largest reach about 1.75 m⁵. In southern Africa they average 90–120 cm⁴.

Distribution

The Reptile Database lists the Gaboon viper from Nigeria, Cameroon, Equatorial Guinea, Gabon, the two Congos, the Central African Republic, Chad and South Sudan east to Uganda, western Kenya, Rwanda and eastern Tanzania, and south to Angola, Zambia, Malawi, Mozambique, eastern Zimbabwe and Zululand in South Africa¹. Gaboon vipers from Guinea to Ghana and Togo in West Africa, once a subspecies, are now treated as a separate species, the western Gaboon viper (Bitis rhinoceros)^2,3. In South Africa this snake is found only in the far north-east of KwaZulu-Natal, from Mtunzini northwards along the coast^4,7.

Habitat

Gaboon vipers live mainly in rainforest and other moist forest, where they lie hidden in the leaf litter on the forest floor¹⁰. They also occur in coastal and montane forest and in savanna⁵. In South Africa they depend on coastal forest, much of it inside the iSimangaliso Wetland Park, where radio-tracked snakes chose spots with dense undergrowth close to trees and shrubs¹². In the cooler months they moved to more open areas, probably to keep warm¹².

Behaviour

The Gaboon viper is mainly active at night, although it often basks at the edges of forests⁴. It hunts by ambush^10,12. Radio-tracked snakes in South Africa often stayed still at one ambush site for weeks, frequently within a metre of an antelope trail, and one stayed in a single spot for 87 days in winter¹². It is surprisingly placid⁴. If threatened, it may raise the front of its body and give a series of long, drawn-out hisses⁴.

Diet

In southern Nigeria, a study of 524 Gaboon vipers found that they ate mainly small mammals, followed by birds, lizards and occasionally frogs¹¹. Young snakes ate more newborn mice and lizards than adults did¹¹. In South Africa, Gaboon vipers have been recorded taking prey close to their own body weight, such as a red duiker, a small forest antelope¹².

Reproduction

The Gaboon viper gives birth to live young^1,10. Litters of about 20 to 50 young have been reported, and newborns are up to about 30 cm long and already show the adult pattern¹⁰. Females grow larger than males¹¹. In South Africa, both sexes moved around most at the start of the breeding season, in March¹².

Venom and medical significance

The Gaboon viper’s venom is strongly cytotoxic and also haemotoxic, causing severe pain, spreading swelling, bleeding from the fang punctures, blistering and tissue damage⁷. It is credited with the longest fangs of any snake in the world⁹, at more than 4 cm⁸, and a large Gaboon viper can deliver about twice as much venom as a puff adder⁷. Bites are rare because it is placid and seldom met, and in South Africa almost all known bites have been to people keeping captive snakes^7,9. In a review of five bites from captive Gaboon vipers, patients had progressive swelling, local tissue death and slow blood clotting, and one person died after being unable to call for help¹³. The World Health Organization ranks it as of highest medical importance (Category 1) in countries such as Nigeria, Cameroon, the Democratic Republic of the Congo, Uganda and Zambia, and South Africa’s SAVP polyvalent antivenom has covered its venom since 1938^3,14. Anyone bitten should go to hospital immediately.

Conservation

The Gaboon viper is listed as Vulnerable on the IUCN Red List (assessment published in 2021)¹⁶. In South Africa it is threatened by habitat destruction and has been assessed as Near Threatened⁴. A study of the South African population suggested that it is doing better than was once thought, but that the coastal dune forest it relies on needs long-term protection¹².

Similar species

The puff adder (Bitis arietans) is another heavy-bodied ambush adder¹⁵, and the two species have been recorded hybridising in the wild¹. The Gaboon viper’s large, pale head with a dark central line, and its pattern of pale rectangles and hourglass shapes, help to tell it apart^9,10. In West Africa, the western Gaboon viper (Bitis rhinoceros) has a single dark triangle below each eye rather than two, and usually a more obvious pair of horns on the nose⁶.

These differences are not a safe basis for handling any snake. Keep your distance from every snake you cannot identify.

In captivity

The Gaboon viper is a dangerous venomous snake and is not suitable as a pet. Bites from captive Gaboon vipers have caused serious injury and at least one death, and doctors have warned of the dangers of keeping exotic African snakes¹³. In South Africa, almost all recorded bites have been to snake keepers⁷.