Common names: prairie rattlesnake,^[2] western rattlesnake,^[3] plains rattlesnake,^[4] more.

Crotalus viridis is a venomous pitviper species native to the western United States, southwestern Canada, and northern Mexico. Currently, two subspecies are recognized, including the nominate subspecies described here.^[2]

Description

This species commonly grows to more than 100 centimetres (3.3 ft) in length. The maximum recorded size is 151.5 centimetres (4.97 ft) (Klauber, 1937). In Montana, specimens occasionally exceed 120 centimetres (3.9 ft) in length; Klauber (1972) mentioned that 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.^[5]

Identification

Identification characteristics will vary depending on which subspecies is encountered. Generally, western 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 western rattlesnake group carries the distinctive triangular-shaped head and pit sensory organs on either side of the head. A key characteristic that can help differentiate a western rattlesnake from other rattlesnakes is the presence of two internasals contacting the rostral.^[6]

Habitat

Habitat characteristics can vary depending on subspecies and range. Generally, western rattlesnakes will occupy areas that have an abundant prey base. Many subspecies occupy somewhat rocky areas with outcrops serving as den sites. Western rattlesnakes have also been known to occupy burrows of other animals. They seem to prefer dry areas with moderate vegetation coverage. Vegetation cover will vary depending on region and subspecies.^[6]

Diet

Western rattlesnakes, because of their expansive distribution, have a wide array of prey items. Generally, this species prefers small mammals such as ground squirrels, mice, rats, small rabbits and prairie dogs. They will occasionally feed on amphibians and reptiles. This is more commonly seen in juvenile snakes.^[6]

Reproduction

Western rattlesnakes are viviparous and can produce anywhere from 1 to 25 young per reproduction event. The average number of young ranges from 4-12 but can vary greatly due to availability of food and environmental conditions. Western rattlesnake females may not necessarily breed every year. C. viridis It is also common for females to give birth at communal den sites. The young are born between the months of August and October.^[6][7]

Behavior

In a defensive posture.

Western rattlesnakes are typically active diurnally in cooler weather and nocturnally during hot weather C. viridis. This species complex is equipped with powerful venom and will defend if threatened or injured. As with other rattlesnake species, western rattlesnakes will rapidly vibrate their tail which produces a unique rasping sound to warn intruders.^[7]

Common names

Prairie rattlesnake,^[2][4] western rattlesnake,^[3] plains rattlesnake, black rattler, prairie rattler, common rattlesnake, confluent rattlesnake, Great Basin rattlesnake, large prairie rattlesnake, Missouri rattlesnake, rattlesnake of the prairies, spotted rattlesnake, Western Pacific Rattlesnake.^[4]

Geographic range

Found in North America over much of the Great Plains the eastern foothills of the Rocky Mountains, and some intermontane valleys of the Rocky Mountains, from southwestern Canada south through the United States to northern Mexico. In Canada it occurs in Alberta and Saskatchewan; in the USA in eastern Oregon, eastern Washington, southern Idaho, most of Montana (where it is one of 10 snake species and the only venomous one), North Dakota, South Dakota, Wyoming, Nebraska, Colorado, Kansas, Oklahoma, Texas, New Mexico, extreme eastern Arizona, and in Mexico in northern Coahuila and northwestern Chihuahua. Its vertical range is from 100 metres (330 ft) near the Rio Grande River to over 2,775 metres (9,104 ft) elevation in Wyoming.^[5]

Wright and Wright (1957) and Klauber (1997) both mention Utah as within the range of this species, including maps showing it confined to the extreme southeastern part of the state.^[4][8]

The type locality is described as "the Upper Missouri [Valley, USA]". An emendation was proposed by H.M. Smith and Taylor (1950) to "Gross, Boyd County, Nebraska."^[1]

Conservation status

This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001).^[9] Species are listed as such due to their wide distribution, presumed large population, or because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend is stable. Year assessed: 2006.^[10]

Subspecies

Taxonomy

The taxonomic history of this species is convoluted. Previously, seven other C. viridis subspecies were also recognized, including abyssus, caliginis, cerberus, concolor, helleri, lutosus and oreganus. However, in 2001 Ashton and de Queiroz published a paper describing 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: on the one hand C. viridis, including the conventional subspecies viridis and nuntius, and on the other 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.^[5][11][12]

See also

• List of crotaline species and subspecies
• Crotalus by common name
• Crotalus by taxonomic synonyms
• Crotalinae by common name
• Crotalinae by taxonomic synonyms
• Snakebite

References

Further reading