Nerodia rhombifer | Illinois Natural History Survey | U of I

Illinois Natural History Survey - University of Illinois

Squamata     suborder Serpentes
Nerodia rhombifer -- Diamondback Watersnake

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Jackson County, IL: photo by Mike Redmer distribution map

Purple shade indicates vouchered specimens. Light blue (cyan) shade indicates photographic records. Yellow shade indicates verified sighting. Slanted hatch indicates pre-1980 records only

NOTE: Not all specimens upon which these maps are based have been verified.

Key Characters: Dark chainlike pattern on the back; back scales strongly keeled; anal plate divided.

Similar Species: Mississippi green water snake, cottonmouth.

Subspecies: Diamondback water snake, N. r. rhombifer.

Description: Large (up to 135 cm TL), stout yellow or light green snake with 25 - 37 dark Y-shaped side markings that meet on the back to enclose a series of light diamonds down the middle of the back. Pattern brightest in juveniles, obscured in some large adults. Belly yellow with dark spots or half-moons that are most numerous toward the tail. Male has conspicuous papillae under the chin.

Habitat: Quiet, permanent backwaters, swamps, sloughs, lakes, and sluggish streams in the southern third of the state, often in very warm water.

Natural History: One of the largest and most pugnacious snakes in Illinois, it bites and defecates repeatedly when handled. Often basks on limbs overhanging water. Active February through September, it hibernates in beaver lodges, muskrat burrows, and mud bottoms. Mates in late April or May and gives birth to 20 or more young from late August through mid-October. Newborn 25-27 cm TL. Diet consists mainly of fish, but frogs are eaten as well. Predators include other snakes and large shore birds. Large numbers are killed by people who mistake them for cottonmouths.

Status: Common along river bottoms and lowland lakes.


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