Prairie Rattlesnake

The prairie rattlesnake or Great Plains rattlesnake (Crotalus viridis) is a venomous pit viper species native to the western United States, southwestern Canada, and northern Mexico. Currently, two subspecies are recognized, including the prairie rattlesnake (C. v. viridis), the nominate subspecies, and the Hopi rattlesnake (C. v. nuntius).

Taxonomy

The taxonomic history of this species is convoluted. Previously, seven other C. viridis subspecies were also recognized, including C. v. abyssus, C. v. caliginis, C. v. cerberus, C. v. concolor, C. v. helleri, C. v. lutosus, and C. v. oreganus In 2001, though, Ashton and de Queiroz described their analysis of the variation of mitochondrial DNA across the range of this species. Their results agreed broadly with those obtained by Pook et al. (2000). Two main clades were identified, east and west of the Rocky Mountains, which they argued were actually two different species: C. viridis, including the conventional subspecies C. v. viridis and C. v. nuntius, and C. oreganus, including all the other traditional subspecies of C. viridis. The authors retained the names of the traditional subspecies, but emphasized the need for more work to be done on the systematics of C. oreganus.

Description

This species commonly grows to more than 100 cm (3.3 ft) in length. The maximum recorded size is 151.5 cm (4.97 ft). In Montana, specimens occasionally exceed 120 cm (3.9 ft) in length; the species reaches its maximum size in this region. One of the most characteristic features is the presence of three or more, usually four, internasal scales.

Identification characteristics vary depending on which subspecies is encountered. Generally, prairie rattlesnakes are usually lightly colored in hues of brown. Patches of dark brown are often distributed in a dorsal pattern. A color band may be seen at the back of the eye. The prairie rattlesnake group carries the distinctive triangle-shaped head and pit sensory organs on either side of the head. A key characteristic that can help differentiate a prairie rattlesnake from other rattlesnakes is the presence of two internasals contacting the rostral.

Distribution and habitat

Prairie rattlesnakes are found in North America over much of the Great Plains, the eastern foothills and some intermontane valleys of the Rocky Mountains, and from southwestern Canada through the United States to northern Mexico. In Canada, they occur in Alberta and Saskatchewan; in the US, they are found in eastern Idaho, most of Montana, North Dakota, South Dakota, Wyoming, Nebraska, Colorado, Kansas, Oklahoma, Texas, New Mexico, northeastern Arizona, and extreme western Iowa, and in Mexico in northern Coahuila and northwestern Chihuahua. Its vertical range is from 100 m (330 ft) near the Rio Grande to over 2,775 m (9,104 ft) in elevation in Wyoming.