Rhinoceros viper, River Jack, Rhinoceros horned viper, Horned puff adder, Bitis nasicornis
Bitis nasicornis is a venomous viper species found in the forests of West and Central Africa. This large viper is known for its striking coloration and prominent nasal "horns." No subspecies are currently recognized. Common names: butterfly viper, rhinoceros viper, river jack.
The Butterfly viper is a venomous snake found in the forests of West and Central Africa. This large viper is known for its striking coloration and prominent nasal "horns." The color pattern consists of a series of 15-18 blue or blue-green, oblong markings, each with a lemon-yellow line down the center. These are enclosed within irregular, black, rhombic blotches. A series of dark crimson triangles run down the flanks, narrowly bordered with green or blue. Many of the lateral scales have white tips, giving the snake a velvety appearance. The top of the head is blue or green, overlaid with a distinct black arrow mark. The belly is dull green to dirty white, strongly marbled, and blotched in black and gray. Western specimens are more blue, while those from the east are more green. Female Butterfly vipers grow larger than males.
Butterfly vipers are found from Guinea to Ghana in West Africa, and in Central Africa in the Central African Republic, southern Sudan, Cameroon, Gabon, Congo, DR Congo, Angola, Rwanda, Uganda, and western Kenya. They live in forested areas, often near water, and rarely venture into woodlands.
Butterfly vipers are solitary and primarily nocturnal creatures. They hide during the day in leaf litter, in holes, around fallen trees or tangled roots of forest trees. Their vivid coloration actually gives them excellent camouflage in the dappled light conditions of the forest floor, making them almost invisible. Although mainly terrestrial, they are also known to climb into trees and thickets, where they have been found up to 3 m (9.8 ft) above the ground. This climbing behavior is aided by a partially prehensile tail. They are sometimes found in shallow pools and have been described as powerful swimmers. Butterfly vipers prefer to hunt by ambush, and probably spend much of their life motionless, waiting for prey to wander by. They are slow-moving but capable of striking quickly, forwards, or sideways, without coiling first or giving a warning. Holding them by the tail is not safe; as it is somewhat prehensile, they can use it to fling themselves upwards and strike. Butterfly vipers are generally placid creatures. When approached, they often reveal their presence by hissing that sounds almost like a shriek; it is said to be the loudest hiss of any African snake.
Small doses of the snake's primarily hemotoxic venom can be deadly. This is unlike the Gaboon viper, the largest of the vipers, which uses a considerably larger amount of venom. Bitis nasicornis has both neurotoxic, as well as hemotoxic venom, as do most other venomous snakes. The hemotoxic venom in rhinoceros vipers is much more dominant. This venom attacks the circulatory system of the snake's victim, destroying tissue and blood vessels. Internal bleeding also occurs.
When not in use, the rhino viper's fangs are folded up into the roof of the snake's mouth. The snake has the ability to control the movement of its fangs. When a rhino viper opens its mouth, it does not necessarily mean that the fangs will flip down into place. The fangs penetrate deep into the victim and the venom flows through the hollow fangs into the wound.
Because of its restricted geographic range, few bites have been reported. No statistics are available.
Relatively little is known about the toxicity and composition of the venom. In mice, the intravenous LD50 is 1.1 mg/kg. The venom is supposedly slightly less toxic than those of B. arietans and B. gabonica. The maximum wet venom yield is 200 mg. One study reported this venom has the highest intramuscular LD50 value—8.6 mg/kg—of five different viperid venoms tested (B. arietans, B. gabonica, B. nasicornis, Daboia russelii and Vipera aspis ). Another showed little variation in the venom potency of these snakes, whether they were milked once every two days or once every three weeks. In rabbits, the venom is apparently slightly more toxic than that of B. gabonica.
In only a few detailed reports of human envenomation, massive swelling, which may lead to necrosis, had been described. In 2003, a man in Dayton, Ohio, who was keeping a specimen as a pet, was bitten and subsequently died. At least one antivenom protects specifically against bites from this species: India Antiserum Africa Polyvalent.
Butterfly vipers are carnivores. They feed mainly on small mammals, but in wetland habitats, they are also known to take toads, frogs, and even fish.
Butterfly vipers are viviparous meaning they give birth to live young. In West Africa, females produce between 6 and 38 young in March-April at the beginning of the rainy season. Each neonate measures 18-25 cm (7-10 in) in total length and is venomous at birth. In eastern Africa, the breeding season is indefinite.
There are no major threats facing Butterfly vipers at present.
The Butterfly viper population number is unavailable at present from open sources and its conservation status has not been evaluated.
