Crotalus viridis

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Crotalus viridis
Crotalus viridis nuntius.jpg
Hopi rattlesnake, C. v. nuntius
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Viperidae
Genus: Crotalus
C. viridis
Binomial name
Crotalus viridis
(Rafinesque, 1818)
Crotalus viridis distribution.png
  • Crotalinus viridis
    Rafinesque, 1818
  • Crotalurus viridis
    — Rafinesque, 1820
  • Crotalus confluentus
    Say In James, 1823
  • Crotalus Lecontei
    Hallowell, 1852
  • C[audisona]. confluenta
    Cope, 1867
  • [Caudisona confluenta] Var. confluenta
    — Cope, 1867
  • [Caudisona confluenta] Var. lecontei
    — Cope, 1867
  • Crotalus confluentus var. pulverulentus
    Cope, 1883
  • Crotalus confluentus var. confluentus
    — Cope, 1883
  • Crotalus confluentus confluentus
    — Cope, 1892
  • Crotalus confluentus lecontei
    — Cope, 1892
  • Crotalus viridis viridis
    Klauber, 1936 [2]

Crotalus viridis (Common names: prairie rattlesnake, [3] western rattlesnake, [4] Great Plains rattlesnake, [5] and others) is a venomous pit viper species native to the western United States, southwestern Canada, and northern Mexico. Currently, two subspecies are recognized, including the nominate subspecies described here. [3]

Venomous snakes are species of the suborder Serpentes that are capable of producing venom, which they use for killing prey, for defense, and to assist with digestion of their prey. The venom is typically delivered by injection using hollow or grooved fangs, although some venomous snakes lack well-developed fangs. Common venomous snakes include the families Elapidae, Viperidae, Atractaspididae, and some of the Colubridae. The toxicity of venom is mainly indicated by murine LD50, while multiple factors are considered to judge the potential danger to humans. Other important factors for risk assessment include the likelihood that a snake will bite, the quantity of venom delivered with the bite, the efficiency of the delivery mechanism, and the location of a bite on the body of the victim. Snake venom may have both neurotoxic and hemotoxic properties.

In biology, a species ( ) is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies.

Subspecies taxonomic rank subordinate to species

In biological classification, the term subspecies refers to a unity of populations of a species living in a subdivision of the species' global range and varies from other populations of the same species by morphological characteristics. A subspecies cannot be recognized independently. A species is either recognized as having no subspecies at all or at least two, including any that are extinct. The term is abbreviated subsp. in botany and bacteriology, or ssp. in zoology. The plural is the same as the singular: subspecies.



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 . However, in 2001 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: on the one hand C. viridis, including the conventional subspecies C. v. viridis and C. v. 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. [6] [7] [8]

<i>Crotalus oreganus abyssus</i> subspecies of reptile

Crotalus oreganus abyssus is a venomous pit viper subspecies found only in the U.S. states of Arizona and Utah.

<i>Crotalus oreganus caliginis</i> subspecies of reptile

Crotalus oreganus caliginis is a venomous pit viper subspecies endemic to South Coronado Island, Mexico.

Crotalus oreganus concolor is a venomous pit viper subspecies found in the western United States. It is a small subspecies known for its faded color pattern.

Common names for this species include prairie rattlesnake and Hopi rattlesnake.


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 centimetres (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. [6]

Internasal scales

In snakes, the internasal scales are those on top of the head between the scales that surround the nostrils. They are usually paired and situated just behind the rostral.

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 triangle-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. [9]

Distribution and habitat

They, and the subspecies mentioned below, are found in North America over much of the Great Plains, the eastern foothills and some intermontane valleys of the Rocky Mountains, from southwestern Canada through the United States to northern Mexico. In Canada, they occur 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 m (330 ft) near the Rio Grande to over 2,775 m (9,104 ft) in elevation in Wyoming. [6]

Great Plains broad expanse of flat land west of the Mississippi River and east of the Rocky Mountains in the United States and Canada

The Great Plains is the broad expanse of flat land, much of it covered in prairie, steppe, and grassland, that lies west of the Mississippi River tallgrass prairie in the United States and east of the Rocky Mountains in the U.S. and Canada. It embraces:

Rocky Mountains mountain range in North America

The Rocky Mountains, also known as the Rockies, are a major mountain range in western North America. The Rocky Mountains stretch more than 4,800 kilometers (3,000 mi) from the northernmost part of British Columbia, in western Canada, to New Mexico in the Southwestern United States. Located within the North American Cordillera, the Rockies are somewhat distinct from the Pacific Coast Ranges, Cascade Range, and the Sierra Nevada, which all lie farther to the west.

United States federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.

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. [5] [10] 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." [2]

Albert Hazen Wright was an American herpetologist and professor at Cornell University. He was also an honorary member of the International Ornithological Congress. He did a great deal of study of the Okefenokee Swamp. In 1955 he won the Eminent Ecologist Award.

Laurence Monroe Klauber American zoologist

Laurence M. Klauber, was an American herpetologist and the foremost authority on rattlesnakes. He was the first curator of reptiles and amphibians at the San Diego Natural History Museum and Consulting Curator of Reptiles for the San Diego Zoo. He was also a businessman, inventor, and contributed to mathematics in his study of the distribution of prime numbers.

Utah A state of the United States of America

Utah is a state in the western United States. It became the 45th state admitted to the U.S. on January 4, 1896. Utah is the 13th-largest by area, 31st-most-populous, and 10th-least-densely populated of the 50 United States. Utah has a population of more than 3 million according to the Census estimate for July 1, 2016. Urban development is mostly concentrated in two areas: the Wasatch Front in the north-central part of the state, which contains approximately 2.5 million people; and Washington County in Southern Utah, with over 160,000 residents. Utah is bordered by Colorado to the east, Wyoming to the northeast, Idaho to the north, Arizona to the south, and Nevada to the west. It also touches a corner of New Mexico in the southeast.

Habitat characteristics can vary depending on subspecies and range. Generally, western rattlesnakes occupy areas with 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. [11] They seem to prefer dry areas with moderate vegetation coverage. Vegetation cover will vary depending on region and subspecies. [9]


In a defensive posture. Crotalus viridis 02.jpg
In a defensive posture.

Western rattlesnakes live on the land, but they can sometimes climb in trees or bushes. Some even rest in crevices or caves. They are typically active diurnally in cooler weather and nocturnally during hot weather C. viridis. This species complex is equipped with powerful venom, using about 20-55 percent of venom in one bite, and will defend themselves if threatened or injured. As with other rattlesnake species, western rattlesnakes will rapidly vibrate their tails, which produces a unique rasping sound to warn intruders. [12]

The venom of the western rattlesnake is a complexly structured mixture of different proteins with enzymes such as proteases and peptidases found among them. [13] Besides the hemotoxine and its tissue destructive effect, the venom also has neurotoxic properties. [14]


Western rattlesnakes, because of their expansive distribution, have a wide array of prey. Generally, this species prefers small mammals, such as ground squirrels, ground nesting birds, mice, rats, small rabbits and prairie dogs. They will occasionally feed on amphibians and reptiles, and sometimes even other snakes. This is more commonly seen in juvenile snakes. [9]


Western rattlesnakes are viviparous and can produce from one to 25 young per reproduction event. The average number of young ranges from four to 12, but can vary greatly due to availability of food and environmental conditions. Males may compete for females during the breeding season, but western rattlesnake females may not necessarily breed every year. [15] They give birth in late summer or early fall, being their breed 22–28 cm long, without the need for parental care. In addition, their pups are toxic as soon as they are born. They reach sexual maturity at three years of age. It is also common for females to give birth at communal den sites with the young born between August and October. [9] [12]

Conservation status

This species is classified as Least Concern 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 they are unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was stable when assessed in 2006. [1]


Crotalus viridis nuntius Klauber, 1935, [3] the Hopi rattlesnake, inhabits the United States from northeastern and north-central Arizona, from the New Mexico border 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 US Highway 66 in the south. [10]

Crotalus viridis viridis(Rafinesque, 1818), [3] the prairie rattlesnake, inhabits the North American Great Plains from the Rocky Mountains to 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. [10]

See also

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  1. 1 2 Frost, D.R.; Hammerson, G.A. & Santos-Barrera, G. (2007). "Crotalus viridis". The IUCN Red List of Threatened Species . 2007: e.T64339A12771847. doi:10.2305/IUCN.UK.2007.RLTS.T64339A12771847.en.
  2. 1 2 McDiarmid RW, Campbell JA, Touré TA. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, Volume 1. Washington, District of Columbia: Herpetologists' League. 511 pp. ISBN   1-893777-00-6 (series). ISBN   1-893777-01-4 (volume).
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  4. "Crotalus ". Integrated Taxonomic Information System . Retrieved 28 November 2006.
  5. 1 2 Wright AH, Wright AA. 1957. Handbook of Snakes of the United States and Canada. Ithaca and London: Comstock Publishing Associates. (7th printing, 1985). 1,105 pp. (2 volumes). ISBN   0-8014-0463-0.
  6. 1 2 3 Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Ithaca and London: Comstock Publishing Associates. 870 pp. 1500 plates. ISBN   0-8014-4141-2.
  7. Viperidae - Crotalinae - 2001 Publications. The Arizona subspecies was further split into its own species, Crotalus cerberus . Archived 26 December 2007 at the Wayback Machine at Wolfgang Wüster Archived 25 September 2006 at the Wayback Machine , School of Biological Sciences, Bangor University. Accessed 7 April 2008.
  8. 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 Evolution15: 269-282. PDF at Wolfgang Wüster, School of Biological Sciences, Bangor University. Accessed 11 July 2016.
  9. 1 2 3 4 Stebbins RC. 2003. A Field Guide to Western Reptiles and Amphibians, Third edition. The Peterson Field Guide Series ®. New York: Houghton Mifflin Company. xiii + 533 pp. ISBN   978-0-395-98272-3.
  10. 1 2 3 Klauber LM. 1997 (Reprint). Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition. Berkeley: University of California Press. 1,580 pp. (2 volumes). (First published in 1956, 1972). ISBN   0-520-21056-5.
  11. Shipley, B.K., D. Chiszar, K.T. Fitzgerald, and A.J. Saviola. "Spatial ecology of Prairie Rattlesnakes (Crotalus viridis) associated with Black-tailed Prairie Dog (Cynomys ludovicianus) colonies in Colorado." Herpetological Conservation and Biology 8, no. 1 (2013): 240-250.
  12. 1 2 C. virdis. Accessed 7 October 2009.
  13. Saviola, A.J., Pla, D., Sanz, L., Castoe, T.A., Calvete, J.J. and Mackessy, S.P., 2015. Comparative venomics of the Prairie Rattlesnake (Crotalus viridis viridis) from Colorado: Identification of a novel pattern of ontogenetic changes in venom composition and assessment of the immunoreactivity of the commercial antivenom CroFab®. Journal of proteomics, 121, pp.28-43.
  14. Reichl, Franz-Xaver. 2008. Taschenatlas der Toxikologie: Substanzen, Wirkungen, Umwelt [=Pocket Atlas of Toxicology: Substances, Effects, Environment ]. (Chapter: "Venoms"). Hamburg: Nikol Verlag. ISBN   978-3868200058. (in German).
  15. C. viridis

Further reading