The African Twig Snakes are distinctive in appearance and unlikely on that continent to be mistaken for any other snake, if indeed the observer notices them. Preying on lizards, frogs and sometimes birds, they conceal themselves in trees but often at a low enough level to be able to also strike at terrestrial prey, which they may swallow upwards after killing it. Their cryptic coloration and apparent ability to freeze or sway gently, as chameleons do, like a twig on a tree (hence the name) makes them hard to spot. Indeed,. they may be more abundant in areas than is immediately obvious.
Thelotornis is characterised by a depressed and flat head, keyhole-shaped pupils, and in T. kirtlandii a projecting canthus rostralis which forms a shallow loreal groove on each side of the head. This allows a certain amount of binocular vision to the snake. In appearance the head at least means that it is unlikely to mistaken for any other African snake. Other characteristics include a very long tail and large back fangs. The iris in the species capensis and kirtlandii is yellow, and presumably therefore also in usambaricus.
The Twig Snakes are also notorious for another reason: among the back-fanged colubrids, they are among the most toxic, ranking alongside the Boomslang. The great Dr Robert Mertens was killed in old age by one of a pair of captive Twig Snakes he was handling, although in fairness these species are not aggressive towards humans. Nevertheless their venom and the fact that they eat relatively hard-to-provide food items makes them unsuitable captives for most keepers.
| QUICK INDEX | ||
| T. capensis, Twig Snake, Vine Snake | T. kirtlandii, Forest Vine Snake, Bird/Twig Snake | T. usambaricus |
| Species | Common Name | Origin | Adult size | Notes |
| Thelotornis | ||||
| T. capensis | Twig Snake, Vine Snake, Savanna Snake | NE RSA, Namibia, Botswana, Swaziland, S Zimbabwe, Mozambique, Zambia, SE Angola, S Dem.Rep. Congo, Malawi, Tanzania | 80-140cm | This species is found in savannah, coastal thicket and forest fringe. It is characterised by a lance-shaped head. It preys predominantly on lizards, but also on frogs, birds and small snakes, and its venom is a potent haemotoxin (see Branch for details): there is no antivenin. Spawls et al note that it is often mobbed by birds. Scalation: 1 loreal: sublabials 7-10: body scales feebly keeled in 19 rows at midbody:, anal plate divided Ventrals: 149-169, subcaudals paired, 126-158: males have fewer ventrals and more subcaudals. Coloration: grey-brown with black and pink flecks with a series of pale diagonal blotches: see also subspecies entries. Reproduction: males engage in combat in the mating season, rivals trying to force the head of the opponent down. The female lays 4-18 eggs in Dec-Jan, which take 60-90 days to hatch. She may lay up to two clutches per season. |
| T. c. capensis | RSA (KwaZulu-Natal, Swaziland, Mpumalanga, N. Province and adj. areas) | 80-136cm | <162 ventrals. Coloration: blue-green head heavily speckled with black. | |
| T. c. mossambicanus | Eastern Twig/Vine Snake | Mozambique | 80-140cm | Intergrades along southern border with other subspecies. May also be considered a full species: see EMBL database entry. Coloration: head uniform green. |
| T. c. oatesis | Oates' Vine Snake | N Botswana, N Namibia, Zimbabwe, Zambia | 90-168cm | >162 ventrals. Coloration: blue-green head with a black Y shape on the crown (black and pink in East Africa) |
| T. c. schilsi | ? | ? | Not mentioned in Branch and apparently hardly distinguishable from T. c. mossambicanus: see EMBL database entry. | |
| T. kirklandii | Forest Vine Snake, Bird Snake, Twig Snake | Most of W & E Africa as far south as Angola, Dem. Rep. Congo and Tanzania and Uganda | 48-66": max. 83" | Noble and Schmidt noted the abundance of this species in the rain forest of Gaboon and Cameroon, where it preys on birds and tree lizards. They also noted that the tail frequently appeared to be injured. Spawls et al note that within the forest in East Africa it seems to be most abundant around natural glades. Scalation: 1 preocular, 3 postoculars, 1-3 temporals, 8-9 supralabials, 10-13 sublabials, usually 2 loreals, usually 3 enlarged occipitals behind parietals (5 once recorded). Dorsal rows: 19 (N&S give the formula 19-19-13). Ventral plates: 173-189, on average higher in females: 150-157 (male) or 140-154 (female) subcaudals. Coloration: subtle mixture of greens, browns, greys and pinks: ventrally predominantly pink. Top of head uniform green. Neck has black crossbars which become much more distinct when the neck is distended, an interesting effect of a striking warning display in an otherwise cryptically camouflaged animal (Noble & Schmidt, citing Müller 1910). |
| T. usambaricus | Tanzania (E Usambara mtns), Kenyan coast | ? | This species appears to be T. c. mossambicus raised to full species level: see EMBL database entry. Not mentioned by Spawls et al (2002). | |
Field Guide to the Reptiles of East Africa by Stephen Spawls, Kim Howell, Robert Drewes and James Ashe. Detailed and invaluable review of all reptile species in the region.
Snakes and other Reptiles of Southern Africa, Bill Branch, Struik. Very good overview of all reptiles in the region with identification details.
Herpetology of Congo, R Noble and K P Schmidt, 1923, SSAR reprint 1998. Still considered one of the main guides to the Congo basin and Sudanese savannah areas of Africa, although some taxonomy has changed.
None so far.
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