View source for Twig snake

{{Short description|Genus of snakes}}
{{redirect|Bird snake|the species from Mexico, Central America and South America|Phrynonax poecilonotus|the monotypic genus and its sole representative the Brazilian bird snake|Rhachidelus}}
{{Automatic taxobox 
| image             = Vine Snake (Thelotornis capensis) (6011690147).jpg
| image_caption     = ''T. capensis'' in [[Kruger National Park|Kruger NP]], South Africa
| name              = Twig snake
| taxon             = Thelotornis
| authority         = [[Andrew Smith (zoologist)|A. Smith]], 1849<ref>"''Thelotornis'' ". ''Dahms Tierleben''. www.dahmstierleben.de/systematik/Reptilien/Squamata/Serpentes/colubroidea/colubridae/colubrinae.</ref>
| subdivision_ranks = [[Species]]
| subdivision       = Four species, see text.
}}

The '''twig snakes''' ([[genus]] '''''Thelotornis'''''), also commonly known as '''bird snakes''' or '''vine snakes''',  are a genus of [[Opisthoglyphous|rear-fanged]] [[venomous snake]]s in the [[Family (biology)|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 [[Snake scales|scale]]s. Twig snake bites are potentially deadly: the venom is [[hemotoxin|hemotoxic]], affecting the blood clotting mechanism and causing uncontrolled bleeding and internal hemorrhaging.<ref>{{cite web|url=https://www.africansnakebiteinstitute.com/snake/twig-snake/|title=Twig snake|website=African Snakebite Institute|accessdate=23 June 2018}}</ref> 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.<ref>{{EMBL genus|genus=Thelotornis}} www.reptile-database.org.</ref>
{| class="wikitable"
|-
! Image !! Scientific name  !! Common name !! Distribution
|-
|[[File:Vine Snake (Thelotornis capensis) (6011690147).jpg|frameless|upright]] ||''[[Thelotornis capensis]]'' <br />{{small|[[Andrew Smith (zoologist)|A. Smith]], 1849}}|| Savanna vine snake ||southern Africa.
|-
|[[File:NHM London Twig snake (Thelotornis kirtlandii).jpg|frameless|upright]] ||''[[Thelotornis kirtlandii]]'' <br />{{small|([[Edward Hallowell (herpetologist)|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.
|-
|[[File:Eastern Vine Snake (Thelotornis mossambicanus) (13937474977).jpg|frameless|upright]] ||''[[Thelotornis mossambicanus]]'' <br />{{small|([[José Vicente Barbosa du Bocage|Bocage]], 1895)}}|| Eastern vine snake||Eastern Africa.
|-
|[[File:Thelotornis usambaricus.jpg|frameless|upright]] ||''[[Usambara vine snake|Thelotornis usambaricus]]'' <br />{{small|[[Donald George Broadley|Broadley]], 2001}}||Usambara vine snake  ||Tanzania (East Usambara Mts), Kenya (coast), Mozambique
|-
|}

''[[Nota bene]]'': A [[Binomial nomenclature|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.<ref>[[species:Coleman Jett Goin|Goin, Coleman J.]]; [[species:Olive Lynda Bown Goin|Goin, Olive B.]]; [[species:George Robert Zug|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).</ref> 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 [[Camouflage|conceal]] themselves in [[tree]]s, 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 [[chameleon]]s 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 (herpetology)|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''.


==Gallery==
<gallery>
File:Southern vine snake (Thelotornis capensis capensis).jpg|{{center|''T. capensis''}}
File:Thelotornis capensis mossambicanus.jpg|{{center|''T. mossambicanus''}}
</gallery>

==References==
{{Reflist}}

==Further reading==
*[[George Albert Boulenger|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.&nbsp;184–185).
*[[William Roy Branch|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.&nbsp;100).
*[[Andrew Smith (zoologist)|Smith A]] (1849). ''Illustrations of the Zoology of South Africa, Reptilia''. London: Smith, Elder, and Co. (''Thelotornis'', new genus).

==External links==
{{Wikispecies|Thelotornis}}
*{{EOL|2289250|''Thelotornis ''}}
*{{NCBI taxid|186608|''Thelotornis ''}}

{{Taxonbar|from=Q2284459}}

[[Category:Twig snake]]
[[Category:Venomous snakes]]
[[Category:Taxa named by Andrew Smith (zoologist)]]