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Thamnophis elegansWestern Terrestrial Garter Snake

By Jake Whitaker

Geographic Range

Thamnophis elegans, the western terrestrial garter snake, is found in North America, ranging from northern Mexico to Canada. In Mexico, they can be found in northern Baja California. In the United States, T. elegans ranges from New Mexico to western Oklahoma and Nebraska, through the Dakotas to the Canadian border and west to the Pacific Coast. In Canada, it can be found throughout the central and southern regions of Saskatchewan, Alberta, and Manitoba. (Frost, et al., 2013)

Habitat

Western terrestrial garter snakes are often found near water, but can be found in water as well. They are most commonly found around lakes and slow flowing streams, but occur in deserts, plains, mountains, meadows, and forests as well. When these snakes hibernate during winter, they often move into rocky areas. Thamnophis elegans can be found at elevations ranging from sea level to 3993 meters. (Frost, et al., 2013)

  • Range elevation
    0 to 3993 m
    0.00 to 13100.39 ft

Physical Description

Western terrestrial garter snakes generally have grayish-green backs and yellow bellies. Along the sides, they have a yellow stripe that runs the length of the body. Dark spots occasionally occur on the back. There are also melanistic variants of T. elegans. They have 8 upper labial scales that border the mouth, and 10 lower labial scales along the jaw. The 6th and 7th upper scales are higher than they are wide, because there are glands in the upper jaw. A snake will grow longer as it ages, until 1 year after sexual maturity. This species exhibits sexual dimorphism, as females are bigger than males. Common garter snakes (Thamnophis sirtalis), a close relative of western terrestrial garter snakes, grows to 150 grams. Western terrestrial garter snakes produce a very mildly neurotoxic venom, but do not pose a threat to people as they cannot effectively deliver the venom to anything but their small prey. (Cossel Jr, 2000; Wechsler, 2001)

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

Development

Thamnophis elegans has a 2 to 3 month gestation period. The female retains the eggs within her until the young are born. After the female gives birth to the newborns, they are left to defend themselves. On average, they are about 23 cm long at this point. Young snakes immediately start to feed in order to survive the long winter hibernation. Young snakes are more aggressive than adults when feeding. These snakes become mature at 2 years of age. (Gould, 2013; Kaplan, 2000)

Reproduction

Usually western terrestrial garter snakes mate in the spring, but mating can also occurs in the fall. Males become sexually active when the air temperature beings to rise. They produce sperm at the end of summer, which is then stored until springtime mating. Females produce eggs about the same time. Courtship begins when the temperature rises in the spring and females release a pheromone to alert males they are ready to mate. Once females have mated, they move out of the den where they were inseminated. Males stay in the den to continue mating. This suggests females with multiple male partners is the result of sexual conflict. (Garner and Larsen, 2005; Gould, 2013)

Females give birth to live young after retaining the eggs in their bodies. The timing of reproduction varies based on latitude and climate. Litter size can vary based on how many males mated with a female. They typically produce 8 to 12 offspring per mating, although 4 to 19 have been recorded. In addition, females that were heavier before insemination tend to have larger litters. (Garner and Larsen, 2005; Gould, 2013)

  • Breeding interval
    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
    12
  • 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. The young venture out to eat anything they can find before temperatures drop too low. In order to survive the winter the young need to be aggressive in acquiring food. (Gould, 2013; Kaplan, 2000)

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

Lifespan/Longevity

The lifespan of Thamnophis elegans varies based on habitat. Some populations found in high elevation or near lakes have shorter lifespans. They grow quickly, reproduce early in their lives, and produce more offspring. Individuals in other populations, at lower elevations have longer lifespans. They do not mature as quickly and produce fewer offspring with each breeding season. The most common causes 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 T. elegans is similar. (Bronikowski and Vleck, 2010; Harding, 1997; Wechsler, 2001)

Behavior

Local climate and seasons dictate when western terrestrial garter snakes are active. Mornings are spent warming up in the sun. They bask on surfaces that absorb and retain solar heat. Once warmed up, they are most active during the day and spend time hunting. These snakes require energy to invest in reproduction and they need to eat enough to survive winter hibernation. 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 active times of the year. They den communally for winter hibernation and if they become dormant during the summer. They are likely to return to the same rocky hibernation site annually. (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)

Communication and Perception

Western terrestrial garter snakes have well-developed senses of taste and smell but poor eyesight and poor depth perception. Their senses of taste and smell are combined and sensed through the Jacobson's organ, a series of sensory pits at the roof of the mouth. This organ is employed when a snake thrusts its tongue out, allowing the snake to "taste" the air, and it quickly withdraws its tongue back into the mouth to further process the sensation by rubbing the tongue on the sensory pits. They can perceive small movements and follow them closely. They can sense vibrations, but it is unclear if they can hear well with their ears. These snakes have a chemical that is secreted from their cloaca and musk glands when threatened. The chemical has a foul odor that the snake rubs on itself and onto the threat when there is contact. Females also use a pheromone to alert males they are ready to mate. (Gould, 2013; Hallock and McAllister, 2009)

Food Habits

Coastal populations of western terrestrial garter snakes primarily eat organisms that are found on land. Their prey includes slugs, salamanders, small mammals, and lizards. Individuals that live in inland areas usually hunt in and around water. They commonly eat frog and toad larvae, leeches, and fish. They hunt by looking for movements and observing chemical cues with their Jacobson’s organs. When they bite into prey they keep a firm hold. Venom paralyzes the prey just enough for the snake to swallow it whole. Until they are large enough to eat normal prey, young snakes eat insects and other invertebrates. (Drummond and Burghardt, 1983; Gould, 2013)

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

Predation

Western terrestrial garter snakes avoid predation by blending into their surroundings using cryptic coloration. When they feel threatened, they secrete the contents of their cloaca. The secretion has a bad odor that the snake will rub on itself and on predators when attacked. They may also attempt immobility, depending on body temperature and other strategies already employed. They are preyed on by a wide variety of predatory birds and mammals. (Cossel Jr, 2000; Gregory and Gregory, 2006; Isaac and Gregory, 2012; Sparkman, et al., 2013)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Western terrestrial garter snakes are negatively impacted by predation from predatory birds as well as mammals such as opossums, raccoons, and minks. They feed on frogs, worms, lizards, slugs, small mammals, and sometimes fish. Garter snakes have been recorded with trematode infections. (Drummond and Burghardt, 1983; Kaplan, 2000; Sparkman and Palacios, 2009; Sparkman, et al., 2013)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

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

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

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)

Conservation Status

Western terrestrial garter snakes are considered least concern by the IUCN Red List. There are rough estimates of there at least 100,000 mature individuals in the wild, and there are no significant threats to this species. In addition, many populations live in protected areas. (Frost, et al., 2013)

Contributors

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

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

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

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.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

forest

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

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

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.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

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

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

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.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

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). http://imnh.isu.edu. Accessed November 05, 2013 at http://imnh.isu.edu/digitalatlas/bio/reptile/serp/thel/thelfram.htm.

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). lucnredlist.org. Accessed November 05, 2013 at http://www.iucnredlist.org/details/63976/0.

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). www.thamnophis.com. Accessed November 13, 2013 at http://www.thamnophis.com/archive/articles/artic22.htm.

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 http://www1.dnr.wa.gov/nhp/refdesk/herp/html/4thel.html.

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). www.anapsid.org. Accessed November 13, 2013 at http://www.anapsid.org/gartcare.html.

Savonen, C. 2007. "Garter snakes benefit garden ecosystem" (On-line). oregonstate.edu. Accessed November 05, 2013 at http://extension.oregonstate.edu/gardening/node/972/print.

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.

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