twig snake

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 deadly: the venom is hemotoxic, affecting the blood clotting mechanism and causing uncontrolled bleeding and internal hemorrhaging. Bites by twig snakes have caused death in humans; famous herpetologist Robert Mertens died after being bitten by his pet savanna vine snake (''Thelotornis capensis''). However, envenomed bites are extremely rare when not handling the snake, as the fangs can't breach the skin except in a few places like the web between the thumb and fingers.

Species

The genus ''Thelotornis'' contains four species which are recognized as being valid.

''Nota bene'': A binomial authority in parentheses indicates that the species was originally described in a genus other than ''Thelotornis''.

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 birds, lizards and frogs, 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.

Description

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''.

Etymology

The specific name, ''kirtlandii'', is in honor of American naturalist Jared Potter Kirtland.Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). ''The Eponym Dictionary of Reptiles''. Baltimore: Johns Hopkins University Press. xiii + 296 pp. . ("''Thelotornis kirtlandi'' ic, p. 142).

Gallery

File:Southern vine snake (Thelotornis capensis capensis).jpg,
File:Thelotornis capensis mossambicanus.jpg,
File:NHM London Twig snake (Thelotornis kirtlandii).jpg,

References

Further reading

* 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. . (Genus ''Thelotornis'', p. 100).
*Smith A (1849). ''Illustrations of the Zoology of South Africa, Reptilia''. London: Smith, Elder, and Co. (''Thelotornis'', new genus).

External links

*
*

{{Taxonbar, from=Q2284459

Colubrids
Venomous snakes