|T. capensis in Kruger NP, South Africa|
A. Smith, 1849
Four species, see text.
The twig snakes (genus Thelotornis), also commonly known as bird snakes or vine snakes, are a genus of rear-fanged venomous snakes in the family Colubridae. The genus is native to Africa. All species in the genus have a slender and elongated profile, a long tail, a narrow head, and a pointed snout. The eye of all species has a horizontal pupil, shaped like a keyhole, which gives twig snakes binocular vision. Twig snakes are greyish-brown with faint light and dark markings. When threatened, they inflate the throat to display bold black markings between the scales. Twig snakes are considered to be very dangerous because the venom is haemotoxic, affecting the blood clotting mechanism and causing uncontrolled bleeding. Bites by twig snakes can cause death in humans; famous herpetologist Robert Mertens died after being bitten by his pet Savanna vine snake (Thelotornis capensis).
|Image||Scientific name||Common name||Distribution|
|Thelotornis capensis A. Smith, 1849||Savanna vine snake||southern Africa.|
|Thelotornis kirtlandii (Hallowell, 1844)||Forest vine snake||Angola, Benin, Cameroon, Central African Republic, Congo, DR Congo, Equatorial Guinea, Gabon, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Kenya, Liberia, Nigeria, Sierra Leone, Somalia, Tanzania, Togo, Uganda, and Zambia.|
|Thelotornis mossambicanus (Bocage, 1895)||Eastern vine snake||Eastern Africa.|
|Thelotornis usambaricus Broadley, 2001||Usambara vine snake||Tanzania (East Usambara Mts), Kenya (coast), Mozambique|
Anatomy and behaviour
Twig snakes are among the few rear-fanged colubrids whose bite is highly venomous and potentially fatal. The venom is hemotoxic, and although its effects are very slow, and bites are rare, no antivenom has been developed and several fatalities (such as Robert Mertens) have occurred. They prey on lizards, frogs, and sometimes birds, and conceal themselves in trees, though often at a low enough level to be able to also strike at terrestrial prey, which they may swallow upwards after killing. 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.
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. 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, which allows some binocular vision. In appearance, the head at least is unlikely to be mistaken for any other African snake. Other characteristics include a very long tail and large back fangs. The iris in T. capensis and T. kirtlandii is yellow, and presumably therefore also in T. usambaricus.
- "Thelotornis ". Dahms Tierleben. www.dahmstierleben.de/systematik/Reptilien/Squamata/Serpentes/colubroidea/colubridae/colubrinae.
- "Twig snake". African Snakebite Institute. Retrieved 23 June 2018.
- "Thelotornis ". The Reptile Database. www.reptile-database.org.
- Goin, Coleman J.; Goin, Olive B.; Zug, George R. (1978). Introduction to Herpetology, Third Edition. San Francisco: W.H. Freeman. xi + 387 pp. ISBN 0-7167-0020-4. ("Thelotornis kirtlandi [sic]", p. 322).
- Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. ISBN 978-1-4214-0135-5. ("Thelotornis kirtlandi [sic]", p. 142).
- Boulenger GA (1896). Catalogue of the Snakes in the British Museum (Natural History). Volume III., Containing the Colubridæ (Opisthoglyphæ and Proteroglyphæ) ... London: Trustees of the British Museum (Natural History). (Taylor and Francis, printers). xiv + 727 pp. + Plates I-XXV. (Genus Thelotornis, pp. 184–185).
- Branch, Bill (2004). Field Guide to Snakes and other Reptiles of Southern Africa. Sanibel Island, Florida: Ralph Curtis Books. 399 pp. ISBN 0-88359-042-5. (Genus Thelotornis, p. 100).
- Smith A (1849). Illustrations of the Zoology of South Africa, Reptilia. London: Smith, Elder, and Co. (Thelotornis, new genus).
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