Types: none designated (McDiarmid et al., 1999).

Type-locality: "the Upper Missouri" (Valley, USA). Smith and Taylor (1950) proposed an emendation to "Gross, Boyd County, Nebraska." (McDiarmid et al., 1999).

Prairie rattlesnake

Western rattlesnake

Plains rattlesnake

As defined by Crother et al. (2003), following congruence of Pook et al. (2000), Ashton and de Queiroz (2001), and Douglas et al. (2002), this species encompasses only the ranges of subspecies viridis and nuntius of traditionally defined C. viridis. In other words, the range extends from southern Alberta and southern Saskatchewan in Canada, to the northern fringe of northern central Mexico, west to Idaho, Wyoming, Colorado, and extreme eastern Arizona, east to the Dakotas, western Iowa, Nebraska, central Kansas, central Oklahoma, and western and central Texas in the United States (Stebbins 2003, Campbell and Lamar 2004). The ranges and relationships of Crotalus oreganus and Crotalus viridis in the Four Corners region and in northwestern Colorado need further clarification (Hammerson 1999; Brennan and Holycross, 2004). Its elevational range extends from about 100 m asl near the Rio Grande (Campbell and Lamar 2004) to at least 2,895 m asl (9,500 feet) in Colorado (Hammerson 1999).

Crotalus viridis are found across most of the United States west of Texas and the Dakotas. They are also found in northern Mexico and southwest Canada. (Melli, 1999; LaDuc, 2000)

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (200,000 to >2,500,000 square km (about 80,000 to >1,000,000 square miles)) As defined by Crother et al. (2003), following congruence of Pook et al. (2000), Ashton and de Queiroz (2001), and Douglas et al. (2002), this species encompasses only the ranges of subspecies viridis and nuntius of traditionally defined C. viridis. In other words, the range extends from southern Alberta and southern Saskatchewan to the northern fringe of northern central Mexico, west to Idaho, Wyoming, Colorado, and extreme eastern Arizona, east to the Dakotas, western Iowa, Nebraska, central Kansas, central Oklahoma, and western and central Texas (Stebbins 2003, Campbell and Lamar 2004). The ranges and relationships of Crotalus oreganus and Crotalus viridis in the Four Corners region and in northwestern Colorado need further clarification (Hammerson 1999; Brennan and Holycross, 2004, Herpetol. Rev. 35:190-191). Elevational range extends from about 100 meters near the Rio Grande (Campbell and Lamar 2004) to at least 2,895 meters (9,500 feet) in Colorado (Hammerson 1999).

Continent: Middle-America North-America
Distribution: SW Canada (incl. Alberta, Saskatchewan), W USA (Washington, California, Oregon ?, Montana, South Dakota, New Mexico),  Mexico (Baja California Norte, N Chihuahua, NW Coahuila)  viridis: the Great Plains to the Rocky Mountains and from S Canada to Mexico (N Sonora, N Chihuahua, N Coahuila);
Type locality: “the Upper Missouri”. Restricted to “the prairies between the Cannonball and Heart rivers, within 40 km of the Missouri River in North Dakota” a location far distant from the previous restriction of the type locality to ‘‘vicinity of Kansas City, Missouri’’ (Schmidt, 1953: 226).  nuntius: NE Arizona

Southwestern Canada (southern British Columbia, Alberta and Saskatchewan), western United States, and northern Mexico (Mcdiarmid et al., 1999).

The various subspecies of Crotalus viridis may vary slightly in color. Most are greenish gray or greenish brown in color, although members of one subspecies are black with only slight markings. These rattlesnakes have from 33-55 dark blotches on their back, which flatten into rings on the tail, surrounded by lighter markings. Juviniles have similar markings to adults, but may have higher contrast in coloring. All Crotalus viridis have a rattle at the end of their tail, made up of segments of keratin, which knock together to make a rattling sound. The number of segments varies because each time the snake sheds its skin, it gains another segment. Crotalus viridis is generally about 91.5 cm in length, but can be from 89-114 cm. Males and females are dimorphic in that the number of rings on their tails differs. Males tend to have between 6-15 rings, and females tend to have between 4-11 rings.

There are nine subspecies of Crotalus viridis. Crotalus viridis viridis , or Western or Prairie rattlesnake, is the most widespread and is found in most regions of the species. There are eight others which are mostly named for the region they are found in. They are Grand Canyon rattlesnake (Crotalus viridis abyssus), Coronado Island rattlesnake (Crotalus viridis caliginis), Arizona Black rattlesnake (Crotalus viridis ceberus), Midget Faded rattlesnake (Crotalus viridis concolor), Southern Pacific rattlesnake (Crotalus viridis helleri), Great Basin rattlesnake (Crotalus viridis lutosus), and Hopi rattlesnake (Crotalus viridis oreganus). (LaDuc, 2000; Melli, 1999; Herp-edia, 1998; Reptiles and Amphibians of North Dakota, 1999)

Length: 163 cm

Syntype for Crotalus viridis
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Locality: No Further Locality Data, California, United States, North America

Syntype for Crotalus viridis
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Locality: No Further Locality Data, California, United States, North America

Syntype for Crotalus viridis
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Locality: No Further Locality Data, Oregon, United States, North America

Habitat and Ecology

Systems

• Terrestrial

Crotalus viridis are found mostly in grasslands and prairies, and in brush. Various subspecies can be found in woods, forests, caves, rock ledges, and alongside streams. Crotalus viridis avoids desert. (LaDuc, 2000; Melli, 1999; Crotalus viridis viridis, 1999)

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: savanna or grassland ; chaparral ; forest

Comments: This snake inhabits a wide diversity of habitats, from prairies and arid basins to wooded mountains (Lowe et al. 1986, Degenhardt et al. 1996, Hammerson 1999, werler and Dixon 2000, Stebbins 2003, Campbell and Lamar 2004, Werner et al. 2004). It is primarily terrestrial but sometimes climbs into trees or shrubs. When inactive, it occupies mammal burrows, crevices, caves, or similar secluded sites. Pregnant females may congregate near the winter den until parturition (Gannon and Secoy 1985, Graves and Duvall 1992).

Various habitats from sea level to over 2500 m elevation (McDiarmid et al., 1999).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

In some populations, individuals may migrate up to several km (up to 11 km or more in Wyoming) between winter den and summer range (Duvall et al. 1985, 1990). In Utah, Hirth et al. (1969) found that some individuals move in summer up to about 1.5 km from the winter den.

Exhibits fidelity to winter den site.

Crotalus viridis eat small mammals, ground nesting birds, amphibians, and reptiles, including sometimes other snakes. They locate their prey by using their tongue to sense in airborn chemicals given off by the prey. Then they rapidly strike out at them, biting them with their fangs, then letting them go quickly. Venom is released from their fangs when the snakes strike. It works to immobilize the prey, which the snake then tracks and eats. The venom also works to destroy tissue and help with the digestion of bulkier prey.

Their venom is very deadly. Crotalus viridis use from 20-55% of their stored venom when they bite a small mammal such as a mouse. This is approximately 300 times the amount of venom needed to kill that animal. Venom is stored in glands which are connected to the hollow fangs. Venom is the means used to kill the prey, as the bite of the fangs alone would not usually result in death. The fangs are covered by thin tissue and fold back against the roof of the mouth when the mouth is closed.

During early spring and late fall when the weather is warm, Crotalus viridis hunts during the day. When the weather gets hotter, Crotalus viridis tends to seek shelter during the day and wait until night when it is cooler to hunt. (Greene, 1997; Jacobs, 1999; Kardong et. al., 1998; Kardong, 1996; Melli, 1999; Reptiles and Amphibians of North Dakota, 1999)

Comments: Eats mainly small mammals; also birds, lizards, and rarely amphibians (see Ernst 1992). See Diller and Johnson (1988) for predation rate on small mammals in southwestern Idaho. In British Columbia, gravid females generally did not feed (Macartney and Gregory 1988, Macartney 1989); feeding by gravid females has been observed in some areas (e.g., Idaho, Wallace and Diller, 1990, J. Herpetol. 24:246-253). Juveniles in some regions prey mostly on lizards rather than on small mammals.

The predators of Crotalus viridis include some predatory birds such as red-tailed hawks. When Crotalus viridis senses a predator, it makes a rattling sound to warn it. Smaller snakes tend to wait until the predator is closer to begin rattling, as do pregnant females.

Anti-predator Adaptations: cryptic

Crotalus viridis preys on:
Spermophilus washingtoni
Tamias dorsalis
Tamias merriami

This list may not be complete but is based on published studies.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: This species is represented by a very large number of occurrences. On a range-wide scale, Campbell and Lamar (2004) mapped hundreds of collection sites (see also dot maps in Degenhardt et al. 1996 and Hammerson 1999).

100,000 to >1,000,000 individuals

Comments: Adult population size is unknown but certainly exceeds 100,000.

Mortality tends to be high in first-year young.

May congregate at hibernation dens; formerly many den sites harbored up to several hundred snakes, but most of these populations have been decimated by humans.

Primary predators include humans, various mammalian carnivores, raptors, kingsnakes, whipsnakes, and racers.

Comments: Mostly diurnal in cool weather, active in evening and at night in hot summer weather (morning and late afternoon in far north, Gannon and Secoy 1985). Active primarily from about late March or April to October or November over most of range.

Average lifespan

Status: captivity: 24.1 years.

Maximum longevity: 24.1 years (captivity)

Crotalus viridis mate between March and May. They have internal fertilization; males have a hemipenis which they use for copulation. Females give birth to between 4-21 live young in late summer or early fall. The babies are able to take care of themselves immediately and require no parental care. They are from 22-28 cm long when born and are already venomous. They reach sexual maturity after three years. Males may compete for females during mating season; however, body size of males does not seem to be a trait that contributes to mating success. In areas where females are scarce, males spend more time searching for females, and are not generally observed fighting over females.

(Duvall, 1997; Fitch, 1998; Melli, 1999; Reptiles and Amphibians of North Dakota, 1999; Crotalus viridis viridis, 1999)

Mating occurs mostly from mid-summer to early fall, mainly in late summer in central U.S. (Aldridge, 1993, J. Herpetol. 27:481-484), occasionally in spring. Young are born usually in August-October. Litter size increases with female size (average 5 where body size is small, maximum about 25 in the largest females where body size is large. Individual adult females may not give birth in some years, probably depending on nutritional status; interval between litters was 2 or more years in Wyoming (Graves and Duvall 1992). Requires several years to reach sexual maturity in areas with short growing season. Pregnant females may congregate in small area.

There are currently no conservation measures being taken for Crotalus viridis because their existence is not considered threatened. (Melli, 1999)

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N3 - Vulnerable

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Global Short Term Trend: Relatively stable (=10% change)

Comments: Currently, extent of occurrence, area of occupancy, and number of subpopulations, and population size probably are relatively stable or declining at a rate of less than 10 percent over 10 years or three generations.

Global Long Term Trend: Increase of 10-25% to decline of 50%

Comments: Some local populations have declined or disappeared as a result of historical killing of snakes at dens (Hammerson 1999, Ernst and Ernst 2003).

Major Threats

Comments: No major threats are known. Locally, populations have been eliminated or depleted as a result of killing at dens and loss/degradation of habitat by residential, commercial, and agricultural development (Hammerson 1999).

Conservation Actions

Global Protection: Many to very many (13 to >40) occurrences appropriately protected and managed

Comments: Many occurrences are in protected areas.

The only adverse affect that Crotalus viridis can have on humans is that they may bite an individual that provokes them. Their venom can cause injury and death. (Jacobs, 1999)

Crotalus viridis help to control populations of rodents and other animals that they feed on.

Comments: Venomous.

Comments: Analysis of historical biogeography based on mtDNA data (Pook et al. 2000) revealed two main clades, one including populations from east and south of the Rocky Mountains and the other consisting of populations west of the Rocky Mountains. The conventionally recognized subspecies do not fully correspond to the phylogenetic pattern, and a review of the systematic status of several populations is needed (Pook et al. 2000).

Ashton and de Queiroz (2001) examined mtDNA variation among 26 populations of C. viridis and also identified two main clades: eastern, including subspecies viridis and nuntius (low levels of genetic divergence), and western, including all other subspecies. However, Ashton and de Queiroz (2001) differed from Pook et al. (2000) with respect to the relationships among members of the western clade, although Ashton and de Queiroz studied only a few individuals from each member of the western clade and stated that the relationships within the western clade are largely unresolved and that none (except possibly cerberus) appeared to deserve recognition as separate evolutionary species. Ashton and de Queiroz suggested that the two main clades be regarded as distinct species, C. viridis (eastern clade) and C. oreganus (western clade). The historical biogeographic scenario described by Ashton and de Queiroz (2001) suggests secondary contact between C. viridis and C. oreganus in northern Arizona, southwestern and northwestern Colorado, and southeastern Utah.

Douglas et al. (2002) examined mtDNA variation in C. viridis, with emphasis on the populations on the Colorado Plateau. As did Pook et al. (2000) and Ashton and de Queiroz (2001), they identified eastern and western clades, with the former including the nominal subspecies viridis and nuntius and the latter encompassing all of the other subspecies. Douglas et al. (2002) argued that all of the western subspecies should be recognized as species, but they did not effectively indicate details of distributional relationships in the contact zones among the proposed species. Douglas et al. (2002) concluded that the taxon nuntius should be regarded as a synonym of viridis.

Crother et al. (2003) considered all of the foregoing evidence and adopted the two-species taxonomy (Crotalus oreganus, Crotalus viridis) that is supported by the congruence among all three studies cited above. Campbell and Lamar (2004) also recognized only the two species. However, further clarification of the distributions of C. viridis and C. oreganus is needed, particularly in the contact zones in northern Arizona, southwestern and northwestern Colorado, and southeastern Utah. For example, populations in northwestern Colorado (Moffat County) identified by Douglas et al. (2002) as C. viridis were mapped as C. oreganus concolor by Campbell and Lamar (2004).

Venom characteristics indicate hybridization between C. viridis and C. scutulatus in New Mexico (Glenn and Straight 1990).