Hydrodynastes gigas is a New World species of large, rear-fanged, Dipsadin snake endemic to South America.

[7] Additional South American common names include mboi-peba, surucucu-do-pantanal, and víbora ladradora ('barking snake').

[8] H. gigas is a large dipsadidae snake that may exceed 3 m (9 to 10 ft) in total length (including tail) when adult.

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

The ventral scales are yellow or brown, spotted with dark flecks that make three dotted lines, which appear to merge towards the tail.

[8] H. gigas generally lives in wet, humid areas, and marshlands,[5] typically within the tropical rainforests that are common within its range.

In the wild, H. gigas primarily feeds on fish and amphibians, but will take small mammals, rodents, birds, and even other reptiles.

The posterior maxillary teeth of H. gigas are enlarged, and the Duvernoy's gland produces a secretion with high proteolytic activity.

Besides the ability of this large and powerful snake to inflict mechanical trauma, numerous cases of local envenomation and perhaps hypersensitivity have occurred, most of which have gone unreported.

[citation needed] Manning et al. (1999) described a case in which an 18-year-old male pet-store employee was bitten on the wrist by a specimen that hung on for 1.5 minutes.