Crotalus viridisviridis

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Geographic Range

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)

Habitat

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)

Physical Description

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)

Reproduction

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)

Lifespan/Longevity

  • Average lifespan
    Status: captivity
    24.1 years
    AnAge

Behavior

Crotalus viridis are not aggressive. They usually flee if given the opportunity. They can be found in dense populations in some areas.

During winter and in cold areas, Crotalus viridis hibernates in caves or burrows of other animals. If hibernation places are scarce, as many as one hundred snakes may share one den. These snakes may even hibernate with other species. In warm weather, Crotalus viridis basks in the sun during the day, but in hot weather they seek shelter during the day and come out to hunt at night.

Crotalus viridis use their eyes and sensory pits to detect prey and predators. Pits are heat sensing membranes between a snake's eye and nostril on both sides of its face. They can be used to find prey in the dark and can sense something up to 100 yards away. They also use their tongues to sense the chemicals in the air that are given off by other animals; they flick their tongues in the air to accomplish this. (Greene, 1997; LaDuc, 2000; Melli, 1999; Reptiles and Amphibians of North Dakota, 1999)

Food Habits

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)

Predation

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

Economic Importance for Humans: Positive

Crotalus viridis help to control populations of rodents and other animals that they feed on. (Fitch, 1998; Greene, 1997; Melli, 1999)

Economic Importance for Humans: Negative

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)

Conservation Status

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

Other Comments

The name Crotalus comes from the Greek word "crotalon", which means "little bell", and is used to describe the rattle. The name viridis comes from the latin word for the color green.

Crotalus viridis can live up to twenty-one years. 95% of deaths of Crotalus viridis occur during the active season, rather than the winter. (Greene, 1997; Melli, 1999)

Contributors

Laura Valle (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

sedentary

remains in the same area

solitary

lives alone

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

Duvall, D., G. Schuett. 1997. Straight-line movement and competitive mate searching in prairie rattlesnakes, Crotalus viridis viridis. Animal Behavior, 54(2): 329-334.

Fitch, H. 1998. The Sharon Springs roundup and prairie rattlesnake demography. Transactions of the Kansas Academy of Science, 101(3-4): 101-113.

Greene, H. 1997. Snakes. Berkely: University of California Press.

Jacobs, J. 1999. "The Rattlesnakes of Arizona" (On-line). Accessed March 25, 2000 at http://www.geocities.com/Athens/Olympus/4844/rattlesnake.htm.

Kardong, K. 1996. Mechanical damage inflicted by fangs on prey during predatory strikes by rattlesnakes, Crotalus viridis oreganus. Bulletin of the Maryland Herpetological Society, 329(4): 113-118.

Kardong, K., V. Bels. 1998. Rattlesnake strike behavior: Kinematics. Journal of Experimental Biology, 201(6).

Kissner, K., M. Forbes. 1997. Rattling behavior of prairie rattlesnakes in relation to sex, body size, and body temperature. Ethology, 103(12): 1042-1050.

LaDuc, T. 2000. "Herps of Texas - Snakes" (On-line). Accessed March 23, 2000 at http://www.zo.utexas.edu/research/txherps/snakes/crotalus.viridis.html.

Melli, J. 1999. "San Diego Natural History Museum Field Guide: Crotalus Viridis" (On-line). Accessed March 23, 2000 at http://www.sdnhm.org/fieldgude/herps/crot-viridis.

Unknown, 1999. "Crotalus viridis viridis (Prairie Rattlesnake)" (On-line). Accessed March 23, 2000 at http://ntri.tamuk.edu/herpetarium/viperidae/c.v.viridis/cvviridis.html.

Unknown, 1998. "Herp-edia" (On-line). Accessed March 23, 2000 at http://www.Herp-edia.com/Rattlesnakes.

Unknown, 1999. "Reptiles and Amphibians of North Dakota" (On-line). Accessed March 23, 2000 at http://www.npwrc.usgs.gov/resource/distr/herps/.