Diamond-Backed Watersnake Nerodia rhombifer

Adult from southern Illinois

Identification

Indiana's largest watersnake is quite distinctive; sporting dark bars and dashes that form a chain-link diamond pattern down its back. Most individuals are relatively light-colored gray to olive-green with red eyes that site more squarely on top of the head than most Indiana snakes. Though most adults are three to four feet (90 cm - 1.2 m) long, some individuals may approach five and a half feet (1.6 m) in length.

Juvenile from Posey County

Northern Watersnakes are common in the same bodies of water as this species, but have large, dark brown blotches instead of narrow bars and bands, as in this species.

Ecology and Conservation

This species is highly aquatic and can be found in lakes, ponds, swamps, marshes, ditches, and streams. Its diet consists mostly of slow-moving fish and amphibians. When threatened, specimens exhibit defensive behavior and will not hesitate to bite. During warmer weather, this species becomes strongly nocturnal, although they can commonly be seen basking on logs or branches near water. When alarmed, they drop noisily into the water from their basking site and are capable of remaining underwater for more than an hour.

The Diamond-Backed Watersnake’s diet consists mostly of slow-moving fish (as seen below) and amphibians. Diamond-Backed Watersnakes can be quite beneficial to fishing in the area help to thin out over populated lakes and ponds by feeding on sick and weak fish.

Adult eating a catfish from southeastern Missouri

Care should be taken when handling aquatic snakes in the southern Midwest since nonvenomous watersnakes are often mistaken for Cottonmouths. Where Western Cottonmouths will stand their ground or flee slowly when approached, excitably vibrate their tails, and gape their mouths, whereas watersnakes will retreat very quickly or drop into the water without the tail or mouth displays. When cornered, Diamond-Backed Watersnakes exhibit the defensive behavior of flattening their bodies and discharging large amounts of foul smelling substances from their anal musk glands. The Diamond-Backed Watersnake also will not hesitate to bite.

It is considered common at some sites within this range, but is listed as state Threatened in Iowa. This watersnake is locally abundant in Indiana.

Distribution

Diamond-Backed Watersnakes are found only in the southwestern lowlands along the lower Wabash and Ohio Rivers. They are common along sluggish streams and in oxbow lakes and other permanent aquatic habitats, but also frequent adjacent wetlands.

Taxonomy

Only one subspecies of Diamond-Backed Watersnake is recognized--the Northern Diamond-Backed Watersnake (N. r. rhombifer), which is found in Indiana. These snakes are members of the family Colubridae, which is represented by a total of 28 species in Indiana.

Literature Cited

Conant, R. and J. T . Collins. 1998. Reptiles and Amphibians of Eastern and Central North America. Third Edition, Expanded. Houghton Mifflin, New York, NY.

Minton, S. A. Jr. 2001. Amphibians and Reptiles of Indiana. Indiana Academy of Science, Indianapolis, IN.

Distribution Map
Distribution map of Diamond-Backed Watersnake (Nerodia rhombifer)
Photographs