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Western Terrestrial Garter Snake

Thamnophis elegans

What do they look like?

Western terrestrial garter snakes have grayish-green backs and yellow bellies. Along the sides, they have a yellow stripe that runs the length of the body and sometimes dark spots along the back. There are sometimes all black (melanistic) individuals. Females are larger than males and they grow longer until about one year after they mature. Western terrestrial garter snakes are considered mildly venomous, but pose no real threat to people. (Cossel Jr, 2000; Wechsler, 2001)

  • Sexual Dimorphism
  • female larger
  • Average mass
    150 g
    5.29 oz
  • Average length
    107 cm
    42.13 in

Where do they live?

Western terrestrial garter snakes are found in North America from northern Mexico to Canada. In Mexico, they are found in northern Baja California. In the United States, they range from New Mexico to western Oklahoma and Nebraska, through the Dakotas to the Canadian border and west to the Pacific Coast. In Canada, they are found throughout the central and southern regions of Saskatchewan, Alberta, and Manitoba. (Frost, et al., 2013)

What kind of habitat do they need?

Western terrestrial garter snakes are commonly found around lakes and slow flowing streams, but are also found in desert areas, plains, mountains, meadows, and forests as well. When these snakes hibernate during winter, they often move into rocky areas. (Frost, et al., 2013)

  • Range elevation
    0 to 3993 m
    0.00 to 13100.39 ft

How do they grow?

Western terrestrial garter snake females retain their eggs inside their bodies until the young hatch, when they are born live. After the young are born, they are immediately independent. They begin life at about 23 cm long and must begin to feed immediately to store energy for hibernation. (Gould, 2013; Kaplan, 2000)

How do they reproduce?

Usually western terrestrial garter snakes mate in the spring, but mating can also occurs in the fall. Courtship begins when the temperature rises in the spring and females release a pheromone to alert males they are ready to mate. Mating occurs in their hibernation sites. (Garner and Larsen, 2005; Gould, 2013)

Females give birth to live young after retaining the eggs in their bodies during development. They usually have between 8 and 12 young at a time. The timing of reproduction depends on local climate, occurring earlier in southern parts of the range than in northern parts of the range. (Garner and Larsen, 2005; Gould, 2013)

  • How often does reproduction occur?
    Western terrestrial garter snakes mate once a year.
  • Breeding season
    Mating takes place in spring, after hibernation, when temperatures rise.
  • Range number of offspring
    4 to 19
  • Average number of offspring
  • Range gestation period
    2 to 3 months
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Average age at sexual or reproductive maturity (male)
    2 years

Females retain the eggs in their body before they hatch, which is a significant energy investment. However, once western terrestrial garter snakes are born, they are left to defend themselves and there is no further parental care. (Gould, 2013; Kaplan, 2000)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

How long do they live?

Western terrestrial garter snake lifespans vary based on habitat. Some populations found in high elevation or near lakes have shorter lifespans, populations at lower elevations often have longer lifespans. The most common cause of mortality is predation or over winter starvation in young snakes. Common garter snakes, a closely related species, live between 6 and 12 years in captivity, but the average life span in the wild is only 2 years. It is likely that the lifespan of western terrestrial garter snakes is similar. (Bronikowski and Vleck, 2010; Harding, 1997; Wechsler, 2001)

How do they behave?

Western terrestrial garter snake activity patterns depend on local climates and the time of year. Usually, mornings are spent warming up in the sun, they bask on surfaces that absorb and retain solar heat. Once warmed up, they are active during the day and spend time hunting. They return to shelter in the evening before temperatures drop too low. They also retreat to shelter when it is too hot during the summer and emerge from their dens to bask on rocks on warm winter days. They are solitary during their active times of year, but hibernate in groups during winter or during very hot times in the summer. (Cossel Jr, 2000; Gould, 2013; Hallock and McAllister, 2009)

Home Range

The home range size of western terrestrial garter snakes is not reported in the literature and is likely to vary, depending on local habitat quality. (Cossel Jr, 2000; Hallock and McAllister, 2009)

How do they communicate with each other?

Western terrestrial garter snakes have well-developed senses of taste and smell but poor eyesight and poor depth perception. Like other snakes, they use their tongue to pick up chemicals in the air and insert them into pits in the top of their mouth, called a Jacobson's organ, allowing them to "smell" their environment. They can sense movement visually and respond to vibrations. They use chemical cues in mating and use a foul-smelling musk to deter predators. (Gould, 2013; Hallock and McAllister, 2009)

What do they eat?

Western terrestrial garter snakes eat a wide variety of animals, depending on their body size. Young snakes eat mainly insects, slugs, leeches, and worms. Adults prey on salamanders, frog and toad larvae, small fish, slugs, leeches, lizards, and small mammals, such as shrews and rodents. They detect prey through chemical cues. When they strike the prey, they chew their mildly neurotoxic venom into it so that it is paralyzed and can be swallowed. (Drummond and Burghardt, 1983; Gould, 2013)

  • Animal Foods
  • mammals
  • amphibians
  • reptiles
  • fish
  • insects
  • mollusks
  • terrestrial worms

What eats them and how do they avoid being eaten?

Western terrestrial garter snakes avoid predation by blending into their surroundings using cryptic coloration. When they feel threatened, they secrete a musky, foul-smelling substance or they may feign death. They are preyed on by a wide variety of predatory birds and mammals.

  • These animal colors help protect them
  • cryptic

What roles do they have in the ecosystem?

Western terrestrial garter snakes are important predators of small animals and are, in turn, preyed on by larger predators, such as birds and mammals. (Drummond and Burghardt, 1983; Kaplan, 2000; Sparkman and Palacios, 2009; Sparkman, et al., 2013)

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

Western terrestrial garter snakes bite when they feel threatened, such as when they are handled. They are considered mildly venomous, but they are not a threat to people as they have no effective means of delivering the venom and it is only mildly toxic, causing minor irritation. The venom is used by the snake to capture prey and is only delivered to small prey through a chewing action. (Cossel Jr, 2000)

How do they interact with us?

Western terrestrial garter snakes may eat small mammals that are considered pests. (Kaplan, 2000; Savonen, 2007)

  • Ways that people benefit from these animals:
  • controls pest population

Are they endangered?

Western terrestrial garter snakes are considered least concern because they have large populations, are not facing significant threats, and many populations live in protected areas. (Frost, et al., 2013)


Jake Whitaker (author), University of Wyoming, Hayley Lanier (editor), University of Wyoming - Casper, Angela Miner (editor), Animal Diversity Web Staff.


Bronikowski, A., D. Vleck. 2010. Metabolism, body size and life span: a case study in evolutionarily divergent populations of the garter snake (Thamnophis elegans). Integrative and Comparative Biology, 50.5: 880-887.

Cossel Jr, J. 2000. "Thamnophis elegans" (On-line). Accessed November 05, 2013 at

Drummond, H., G. Burghardt. 1983. Geographic variation in the foraging behavior of the garter snake, Thamnophis elegans. Behavioral Ecology and Sociobiology, 12.1: 43-48.

Frost, D., G. Hammerson, B. Hollingsworth. 2013. "Thamnophis elegans" (On-line). Accessed November 05, 2013 at

Garner, T., K. Larsen. 2005. Multiple paternity in the western terrestrial garter snake, Thamnophis elegans. Canadian Journal of Zoology, 83.5: 656-663.

Gould, F. 2013. "An introduction to the natural history of North American garter snakes with basic triage practices" (On-line). Accessed November 13, 2013 at

Gregory, P., L. Gregory. 2006. Immobility and supination in garter snakes (Thamnophis elegans) following handling by human predators. Journal of Comparative Psychology, 120.3: 262-268.

Hallock, L., K. McAllister. 2009. "Western Terrestrial Garter Snake" (On-line). Accessed November 05, 2013 at

Harding, J. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, Michigan: University of Michigan Press.

Isaac, L., P. Gregory. 2012. Can snakes hide in plain view? Chromatic and achromatic crypsis of two colour forms of the Western Terrestrial Garter Snake (Thamnophis elegans). Biological Journal of the Linnean Society, 108: 756-772.

Kaplan, M. 2000. "Garter Snakes" (On-line). Accessed November 13, 2013 at

Savonen, C. 2007. "Garter snakes benefit garden ecosystem" (On-line). Accessed November 05, 2013 at

Sparkman, A., A. Bronikowski, J. Billings, D. Von Borstel, S. Arnold. 2013. Avian predation and the evolution of life histories in the garter snake Thamnophis elegans. The American Midland Naturalist, 170.1: 66.

Sparkman, A., M. Palacios. 2009. A test of life-history theories of immune defence in two ecotypes of the garter snake, Thamnophis elegans. Journal of Animal Ecology, 78.6: 1242-1248.

Wechsler, D. 2001. Garter Snakes. New York: The Rosen Publishing Group, Inc.

University of Michigan Museum of ZoologyNational Science Foundation

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Whitaker, J. 2014. "Thamnophis elegans" (On-line), Animal Diversity Web. Accessed February 19, 2019 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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