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The twig snakes (genus ''Thelotornis''), also commonly known as bird snakes or vine snakes, are a genus of rear-fanged snakes in the family Colubridae. All species have slender and elongated profiles, long tails, narrow heads, and pointed snouts. The eyes of each species have horizontal pupils, shaped like keyholes, which give twig snakes binocular vision. Twig snakes are greyish-brown with faint light and dark markings. When threatened, they inflate their throats to display bold black markings between the scales. Twig snakes are among the few rear-fanged colubrids whose bite is highly venomous and potentially fatal.〔Goin CJ, Goin OB, Zug GR. 1978. ''Introduction to Herpetology, Third Edition''. San Francisco: W.H. Freeman. xi + 387 pp. ISBN 0-7167-0020-4. ("''Thelotornis kirtlandi'' ()", p. 322).〕 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. 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. 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 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''. The subspecies of ''T. capensis'', ''T. c. mossambicanus'' is sometimes considered a distinct species. ==Etymology== The specific name, ''kirtlandii'', is in honor of American naturalist Jared Potter Kirtland.〔Beolens B, Watkins M, Grayson M. 2011. ''The Eponym Dictionary of Reptiles''. Baltimore: Johns Hopkins University Press. xiii + 296 pp. ISBN 978-1-4214-0135-5. ("''Thelotornis kirtlandi'' ()", p. 142).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Twig snake」の詳細全文を読む スポンサード リンク
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