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.
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.
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.
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.
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.
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.
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.
Prairie rattlesnake, western rattlesnake, 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.
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.
This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001). 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.
|Subspecies||Taxon author||Common name||Geographic range|
|C. v. nuntius||Klauber, 1935||Hopi rattlesnake||The United States from northeastern and north-central Arizona, from the New Mexican line to Cataract Creek, including the Little Colorado River basin, the southern section of the Apache Indian Reservation, the Hopi Reservation, and the Coconino Plateau from the southern rim of the Grand Canyon to U.S. Highway 66 in the south.|
|C. v. viridis||(Rafinesque, 1818)||prairie rattlesnake||North American Great Plains from the Rocky Mountains to long. 96° W. and from southern Canada to extreme northern Mexico, including southwestern Saskatchewan, southeastern Alberta, eastern Washington, Idaho in the Lemhi Valley, Montana east of the higher Rockies, southwestern North Dakota, west, central and extreme southeastern South Dakota, western Iowa, central and western Nebraska, Wyoming except for the Rockies, Colorado, central and western Kansas, Oklahoma, extreme southeastern Utah, northeastern Arizona, New Mexico, western and southwestern Texas, northeastern Sonora, northern Chihuahua, northern Coahuila.|
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.
- List of crotaline species and subspecies
- Crotalus by common name
- Crotalus by taxonomic synonyms
- Crotalinae by common name
- Crotalinae by taxonomic synonyms
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- "Crotalus viridis". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=174319. Retrieved 28 November 2006.
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- C. virdis. Accessed 07 October 2009.
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- Crotalus viridis at the IUCN Red List. Accessed 1 September 2007.
- 2001 Categories & Criteria (version 3.1) at the IUCN Red List. Accessed 13 September 2007.
- Viperidae - Crotalinae - 2001 Publications at Wolfgang Wüster, School of Biological Sciences, Bangor University. Accessed 7 April 2008.
- Pook CE, Wüster W, Thorpe RS. 2000. Historical biogeography of the western rattlesnake (Serpentes: Viperidae: Crotalus viridis), inferred from mitochondrial DNA sequence information. Molecular Phylogenetics and Evolution, 15: 269-282. PDF at Wolfgang Wüster, School of Biological Sciences, Bangor University. Accessed 7 April 2008.
- Ashton KG, de Queiroz A. 2001. Molecular systematics of the Western Rattlesnake, Crotalus viridis (Viperidae), with comments on the utility of the D-Loop in phylogenetic studies of snakes. Molecular Phylogenetics and Evolution 21(2):176-189.
- Rafinesque, C.S. 1818. Further Accounts of Discoveries in Natural History, in the Western States. American Monthly Magazine and Critical Review 4 (5): 39-42. ("N. Sp. Crotalinus viridis", p. 41.)