The Gaboon viper (Bitis gabonica), also called the Gaboon adder, is a large and highly venomous species of viper found in the rainforests and savannas of sub-Saharan Africa. It is the largest member of the genus Bitis. Like all other vipers, it is venomous, and it has the longest fangs of any venomous snake – up to 2 inches (5.1 cm) in length – and the highest venom yield of any snake. No subspecies are recognized.
Taxonomy The Gaboon viper was described in 1854 as Echidna gabonica. Lenk et al. (1999) discovered genetic differences between the two conventionally recognized subspecies of B. g. gabonica and B. g. rhinoceros. According to their research, these two subspecies are as genetically different from each other as they are from B. nasicornis. Consequently, they regard the western form as a separate species, B. rhinoceros. The snake's common names include Gaboon viper, butterfly adder, forest puff adder, whisper, swampjack, and Gaboon adder. Originally a name given by the Portuguese, Gabon (Gabão) refers to the estuary on which the town of Libreville was built, in Gabon, and to a narrow strip of territory on either bank of this arm of the sea. As of 1909, Gaboon referred to the northern portion of French Congo, south of the equator and lying between the Atlantic Ocean and 12°E longitude.
Description Adults are typically 125–155 cm (4.10–5.09 ft) in total length (body and tail). The maximum total length of this species is often cited as 205 cm (81 in) for a specimen collected in Sierra Leone, but individuals from this locale are now reclassified as Bitis rhinoceros. The sexes may be distinguished by the length of the tail in relation to the total length of the body: around 12% for males and 6% for females. Adults, especially females, are very heavy and stout. One female measured at 174 cm (69 in) in total length, a head width of 12 cm (4.7 in), a width or circumference of 37 cm (15 in), and a weight of 8.5 kg (19 lb).
In their description of B. gabonica, Spawls et al. (2004) give a total length of 80–130 cm (31.5–51 in), with a maximum total length of 175 cm (69 in), saying the species may possibly grow larger still. They acknowledge reports of specimens over 1.8 m (5.9 ft), or even over 2 m (6.6 ft) in total length, but claim no evidence supports this. A large specimen of 1.8 m (5.9 ft) total length, caught in 1973, was found to have weighed 11.3 kg (25 lb) with an empty stomach. It is the heaviest venomous snake in Africa and one of the heaviest in the world along with the king cobra and eastern diamondback rattlesnake. The head is large and triangular, while the neck is greatly narrowed, only about one-third the width of the head. A pair of "horns" is present between the raised nostrils—tiny in B. gabonica. The eyes are large and moveable, set well forward, and surrounded by 15–21 circumorbital scales. The species has 12–16 interocular scales across the top of the head. Four or five scale rows separate the suboculars and the supralabials, with 13–18 supralabials and 16–22 sublabials. The fangs may reach a length of 55 mm (2.2 in), the longest of any venomous snake. Midbody, the 28–46 dorsal scale rows are strongly keeled except for the outer rows on each side. The lateral scales are slightly oblique. The ventral scales number 124–140, rarely more than 132 in males, rarely less than 132 in females. With 17–33 paired subcaudal scales, males have no fewer than 25, and females no more than 23. The anal scale is single. The color pattern is striking in the open, but in nature, typically among dead leaves under trees, it provides a high degree of camouflage; in a well-kept cage with a suitable base of dried leaves, overlooking several fully exposed specimens completely is easy. The pattern consists of a series of pale, subrectangular blotches running down the center of the back, interspaced with dark, yellow-edged, hourglass markings. The flanks have a series of fawn or brown rhomboidal shapes, with light vertical central bars. The belly is pale with irregular brown or black blotches. The head is white or cream with a fine, dark central line, black spots on the rear corners, and a dark blue-black triangle behind and below each eye. The iris colour is cream, yellow-white, orange, or silvery. A possible Batesian mimic of the Gaboon viper has been found, which is the Congolese giant toad (Sclerophrys channingi); this species of frog seems to resemble the viper's head, which contrasts with its darker-colored body.
Distribution and habitat This species can be found in Guinea, Ghana, Togo, Nigeria, Cameroon, Equatorial Guinea, Gabon, the Republic of the Congo, the Democratic Republic of the Congo, northern Angola, the Central African Republic, South Sudan, Uganda, Kenya, eastern Tanzania, Zambia, Malawi, eastern Zimbabwe, Mozambique, and northeast KwaZulu-Natal Province in South Africa. Mallow et al. (2003) also list Sierra Leone, Senegal, Ivory Coast, and Liberia in West Africa. The type locality is given as "Gabon" (Africa). The Gaboon viper is usually found in rainforests and nearby woodlands, mainly at low altitudes, but sometimes as high as 1500 m above sea level. Spawls et al. (2004) mention a maximum altitude of 2100 m. According to Broadley and Cock (1975), it is generally found in environments that are parallel to those occupied by its close relative, B. arietans, which is normally found in more open country. In Tanzania, this species is found in secondary thickets, cashew plantations, and agricultural land under bushes and in thickets. In Uganda, they are found in forests and nearby grasslands. They also do well in reclaimed forest areas - cacao plantations in West Africa and coffee plantations in East Africa. They have been found in evergreen forests in Zambia. In Zimbabwe, they only occur in areas of high rainfall along the forested escarpment in the east of the country. In general, they may also be found in swamps, as well as in still and moving waters. They are commonly found in agricultural areas near forests and on roads at night.
Behaviour
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