Atheris

Atheris
File:Atheris chlorechis.jpg
Western bush viper, A. chlorechis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Viperidae
Subfamily:	Viperinae
Genus:	Atheris Cope, 1862
Synonyms
Chloroechis Bonaparte, 1849 Atheris Cope, 1862 Poecilostolus Günther, 1863

Atheris is a genus of venomous vipers known as bush vipers. They are found only in tropical subsaharan Africa (excluding southern Africa) and many species have isolated and fragmented distributions due to their confinement to rain forests. In an interesting example of convergent evolution, they show many similarities to the arboreal pit vipers of Asia and South America. Ten species are currently recognized.

Description

They are relatively small in size, with adults ranging in total length (body + tail) from 40 cm (16 in) for A. katangensis to a maximum of 78 cm (31 in) for A. squamigera.

All species have a broad, triangular head that is distinct from the neck. The canthus is also distinct and the snout is broad. The crown is covered with small imbricate or smooth scales, none of which is enlarged. The eyes are relatively large with elliptical pupils. The eyes are separated from the supralabials by 1–3 scale rows and from the nasal by 2–3 scales.

The body is slender, tapering, and slightly compressed. The dorsal scales are overlapping, strongly keeled and have apical pits. Laterally these are smaller than the middorsals. Midbody there are 14–36 rows of dorsal scales. There are 133–175 rounded ventral scales. The subcaudal scales are single and number 38–67. The tail is strongly prehensile and can support the body while suspended from a branch or a twig.

Members of this genus come in an amazing variety of colors and patterns, often within a single species. A. ceratophora and A. squamigera are particularly variable.

Geographic range

They are found in tropical subsaharan Africa, excluding southern Africa.

Some species have only isolated populations, surviving in small sections of ancient rainforest. It is obvious that they once had a much wider distribution, but are now declining.

Habitat

They inhabit rainforest regions, mostly in remote areas far from human activity.

Conservation status

Some species are threatened by habitat destruction.

Behavior

All species are strictly arboreal, although they can sometimes be found on or near the ground.

Diet

Atheris species have been known to prey upon a variety of small amphibians, lizards, rodents, birds, and even other snakes. Some species or populations may specialize in eating frogs, but most have been described as opportunistic feeders. Prey is typically ambushed from a hanging position, held until it has succumbed to the venom and then swallowed.

Reproduction

All Atheris species are ovoviviparous. Mating takes place in September–November and the females give birth to live young in March and April.

Captivity

A. squamigera is reported to do very well in captivity, needing only arboreal access and having no particular temperature requirements. Captive specimens take mice and small birds. However, there have been reports of cannibalism. Food may be refused during the African winter months of July and August.

Venom

Not much is known about their venom except that it is strongly hemotoxic, causing pain, swelling, near death experiences, and blood clotting problems. Until recently, their venom has often been regarded as less toxic than that of many other species, perhaps because bites are uncommon, but this turned out not to be the case. There are now a number of reports of bites that have led to severe hemorrhaging. One case was fatal. Atheris-specific antivenin does not exist and antivenins meant for bites from other species seem to have little effect, although Echis antivenin has been reported to have been of some help in a case of A. squamigera envenomation.

Species

Species	Taxon author	Subsp.*	Common name	Geographic range
A. anisolepis	Mocquard, 1887	0		West central Africa: Gabon, Congo, west DR Congo, north Angola.
A. ceratophora	F. Werner, 1895	0	Usambara bush viper	The Usambara and Uzungwe Mountains in Tanzania.
A. chlorechisT	(Pel, 1851)	0	West African bush viper	West Africa including Guinea-Bissau, Guinea, Sierra Leone, Liberia, Ivory Coast, Ghana, Togo, Benin, isolated locations in Nigeria, Cameroon, Equatorial Guinea and Gabon.
A. desaixi	Ashe, 1968	0	Mount Kenya bush viper	Two isolated populations in Kenya: in the forests at Chuka, south-eastern Mount Kenya, and Igembe in the northern Nyambeni range.
A. hispida	Laurent, 1955	0	rough-scaled bush viper	Central Africa: DR Congo, south-west Uganda, west Kenya.
A. katangensis	de Witte, 1953	0	Upemba bush viper	Restricted to Upemba National Park, Shaba Province in eastern DR Congo.
A. mabuensis	Branch & Bayliss, 2009	0	Mount Mabu forest viper	Mount Mabu and Mount Namuli, northern Mozambique
A. matildae	Menegon, Davenport & Howell, 2011	0	Matilda’s horned viper	south west Tanzania
A. nitschei	Tornier, 1902	1	Great Lakes bush viper	Central Africa from east DR Congo, Uganda and west Tanzania southward to north Malawi and north Zambia.
A. squamigera	(Hallowell, 1856)	0	variable bush viper	West and central Africa: Ivory Coast and Ghana, eastward through southern Nigeria to Cameroon, southern Central African Republic, Gabon, Congo, DR Congo, northern Angola, Uganda, Tanzania (Rumanika Game Reserve), western Kenya and Bioko Island.

*) Not including the nominate subspecies.
^T) Type species.

Taxonomy

Other species may be encountered in literature, such as:

• A. acuminata Broadley, 1998 — western Uganda
• A. broadleyi Lawson, 1999 — Cameroon (East Province)
• A. hirsuta Ernst & Rödel, 2002 — Ivory Coast
• A. rungweensis Bogert, 1940 — south-west Tanzania, north-east Zambia, north Malawi
• A. subocularis Fischer, 1888 — Cameroon (Southwest Province), extreme east Nigeria

Until relatively recently, the following species, all of which are terrestrial, were also included in the genus Atheris:

• Adenorhinos barbouri (Loveridge, 1930) - Uzungwe viper
• Montatheris hindii (Boulenger, 1910) - montane viper
• Proatheris superciliaris (W. Peters, 1855) - lowland viper

Together with Atheris, these four genera are sometimes referred to as the tribe Atherini.

See also

• List of viperine species and subspecies
• Viperinae by common name
• Viperinae by taxonomic synonyms
• Snakebite

Further reading

• Boulenger GA. (1896). Catalogue of the Snakes in the British Museum (Natural History). Volume III., Containing the ...Viperidæ. London: Trustees of the British Museum (Natural History). (Taylor and Francis, printers.) xiv + 727 pp. + Plates I.- XXV. (Genus Atheris, p. 508.)