Bitis nasicornis
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[Photo] Rhino viper. Photographer: User:Dawson http://en.wikipedia.org/wiki/User:Dawson
Common names: rhinoceros viper, river jack.
Bitis nasicornis is a venomous viper species found in the forests of West and Central Africa. A big viper known for its striking color pattern and prominent nasal horns. No subspecies are recognized.
Description
Large and stout, ranging in length from 72 cm to 107 cm. Spawls et al. (2004) mention a maximum length of 120 cm, but admit that this is exceptional, quoting an average length of 60-90 cm. Females become larger than males.
The head is narrow, flat, triangular and relatively small compared to the rest of the body.[2] The neck is thin. They have a distinctive set of 2-3 horn-like scales on the end of their nose, the front pair of which may be quite long. The eyes are small and set well forward.[5] The fangs are not large: rarely more than 1.5 cm in length.[2]
Midbody there are 31-43 dorsal scale rows.[2] These are so rough and heavily keeled that they sometimes inflict cuts on handlers when the snake struggles.[3] There are 117-140 ventral scales[2] and the anal scale is single.[5] Mallow et al. (2003) say that the subcaudals number 16-32 with males having a higher count (25-30) than females (16-19).[2] Spawls et al. (2004) state that there are 12-32 subcaudals, that they are paired, and that males having higher numbers of them.[5]
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.[5] Western specimens are more blue, while those from the east are more green. After they shed their skin, the bright colors fade quickly as silt from their generally moist habitat accumulates on the rough scales.[2]
Geographic range
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. The type locality is listed only as "interior parts of Africa."[1]
Habitat
Occurs in forested areas, rarely venturing into woodlands. Its range is therefore more restricted than B. gabonica.
Behavior
Primarily nocturnal, the 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.[2] Although mainly terrestrial, they are also known to climb into trees and thickets where they have been found up to 3 m above the ground.[3] This climbing behavior is aided by a tail that is prehensile to a certain extent.[2] They are sometimes found in shallow pools and have been described as powerful swimmers.[2][3]
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.[2]
They have been described as generally placid creatures; less so than B. gabonica, but not as bad-tempered as B. arietans. When approached, they often reveal their presence by hissing.[2] Said to produce the loudest hiss of any African snake -- almost a shriek.[5]
Feeding
Prefers to hunt by ambush, probably spending much of its life motionless, waiting for prey to wander by.[5] Froesch (1967) described a captive specimen that would hardly ever leave its hide box, even when hungry, and once waited for three days for a live mouse to enter its hide box before striking. Feeds mainly on small mammals, but in wetland habitats it is also known to take toads, frogs and even fish. One long-term captive specimen, that was regularly fed pre-killed mice and frogs, would always hold on to its prey for several minutes after a strike before swallowing.[2]
Reproduction
In West Africa, the species gives birth to between 6 and 38 young in March-April at the beginning of the rainy season. Neonates are 18-25 cm in length.[5] In eastern Africa the breeding season is indefinite.[3]
Venom
Because of its restricted range, few bites have been reported. No statistics are available.[3]
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.[3] One study reported that this venom has the highest i.m. 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 that there was 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[2]
There are only a few detailed reports of human envenomation. Massive swelling, which may lead to necrosis, had been described.[3] In 2003 a man in Dayton, Ohio, who was keeping a specimen as a pet, was bitten and subsequently died.[7] There is at least one antivenin that protects specifically against bites from this species: India Antiserum Africa Polyvalent.[8]
http://en.wikipedia.org/wiki/Bitis_nasicornis
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