False Water Cobra

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

H. gigas is a large dipsadine snake that may exceed 3 m (10 ft) in length, with most adult specimens reaching about 2 m (7 ft) in length. The average weight is around 1.6 kg (3.5 lb), but some mature specimens can weigh up to 4.5 kg (9.9 lb). 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. Unlike the true cobra, though, the false water cobra stays in a horizontal position when it hoods, rather than rearing into a vertical position. 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. The background coloring and banding generally become darker towards the tail. This colouring gives the false water cobra effective camouflage in its natural rainforest environment. The ventral scales are yellow or brown, spotted with dark flecks that make three dotted lines that appear to merge as they approach the tail. Females are brown ventrally, whilst males are yellow. Females are suggested to have lighter bands and markings on their bodies. This is not an effective way of judging the sex of H. gigas, as coloring differs slightly among all individuals. Hatchlings and juveniles are much darker in coloration and do not have the typical dark eyes of the adults. They more resemble a garter or water snake than their mature counterparts. In captivity, hypomelanistic animals have been produced. These animals vary in coloration, from some having only slightly lighter colored saddles to those that are almost patternless. A melanistic population found in Tocantins in central Brazil was originally described as a new species of Hydrodynastes (H. melanogigas), but genetic evidence indicates that this population is simply a melanistic variant of H. gigas.

Geographic range