Hydrodynastes gigas is a New World species of large dipsadine snake endemic to South America. Aglyphous snake with enlarged posterior maxillary teeth, not grooved, associated with Duvernoy's gland secretions. endemic to South America. Common names include false cobra, false water cobra, South American water cobra, and Brazilian smooth snake. It is also sometimes referred to as boipevaçu, ñacaniná or yacaniná, from the Guarani ñakanina ('alert head'), mboi-peba, surucucu-do-pantanal, and víbora ladradora ('barking snake').

A mildly venomous species, the false water cobra is so named because when it is threatened, it "hoods" as a true cobra (genus Naja) does. Unlike a true cobra, however, it does not rear up, but instead remains horizontal. No valid subspecies are currently recognized.

Description

thumb|A pair of specimens on display at the [[National Zoological Park (United States)|National Zoological Park, Washington, DC]]

H. gigas is a large dipsadine snake that may exceed in length, The average weight is around , but some mature specimens can weigh up to . This species exhibits sexual dimorphism, with males being much smaller than females. The common name false water cobra is an allusion to its ability to flatten its neck, similar to a cobra, as a defensive reaction to make it look larger and more intimidating. H. gigas can flatten not only its neck, but also lower down its body, which is not possible for a true cobra.

Additionally, the pattern and coloration of this Hydrodynastes species superficially resemble those of true water cobras (Boulengerina). The false water cobra has large eyes with circular pupils, allowing good daytime vision. The tongue is black.

The background colour of a mature specimen is an olive green or brown, with dark spots and bands covering much of its body.

Geographic range

H. gigas is found from eastern Bolivia to southern Brazil, and in Paraguay and Argentina. and some are even kept as pets. Captive-bred specimens can become quite tame and trusting, and many exhibit a high level of intelligence. The liquid venom yield ranges from 0 to 50 microliters and the solid venom yield is 1.3 mg.

==References==<!-- Boletim do Museu Paraense Emílio Goeldi 15: 181 -->

Further reading

  • Boulenger GA (1894). Catalogue of the Snakes in the British Museum (Natural History). Volume II., Containing the Conclusion of the Colubridæ Aglyphæ. London: Trustees of the British Museum (Natural History). (Taylor and Francis, printers). xi + 382 pp. + Plates I-XX. (Genus Cyclagras and species Cyclagras gigas, p.&nbsp;144).
  • Duméril A-M-C, Bibron G, Duméril A[-H-A] (1854). Erpétology générale ou histoire naturelle complète des reptiles. Tome septième. Première partie. [= General Herpetology or Complete Natural History of the Reptiles. Volume 7. Part 1.] Paris: Roret. xvii + 780 pp. (Xenodon gigas, pp.&nbsp;761–763).