Animal Diversity Web

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)

• Biogeographic Regions
• nearctic
  • native

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)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• desert or dune
• savanna or grassland
• forest
• mountains

• Other Habitat Features
• suburban
• agricultural
• riparian

• 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)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• 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)

• Mating System
• polygynandrous (promiscuous)

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)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
• ovoviviparous

• 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)

• Key Behaviors
• terricolous
• diurnal
• motile
• sedentary
• hibernation
• aestivation
• daily torpor
• solitary

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)

• Communication Channels
• visual
• tactile
• chemical

• Other Communication Modes
• pheromones

• Perception Channels
• visual
• tactile
• acoustic
• vibrations
• chemical

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)

• Primary Diet
• carnivore
  • eats terrestrial vertebrates
  • piscivore
  • insectivore
  • molluscivore
  • vermivore

• 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

• Known Predators

  • northern harriers (Circus cyaneus)
  • osprey (Pandion haliaetus)
  • sandhill cranes (Grus canadensis)
  • red tailed hawks (Buteo jamaicensis)
  • ring-billed guls (Larus delawarensis)
  • bald eagles Haliaeetus leucocephalus)
  • American robins (Turdus migratorius)
  • great blue herons (Ardea herodias)
  • Brewer's blackbirds (Euphagus cyanocephalus)
  • common crows (Corvus brachyrhynchos)
  • raccoons (Procyon lotor)
  • Virginia opossums Didelphis virginiana)
  • American mink (Neovison vison)

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)

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)

• IUCN Red List

  Least Concern

• US Federal List

  No special status

• CITES

  No special status

Con­trib­u­tors

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

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.