Common gartersnake (Thamnophis sirtalis)

Close up of a coiled common gartersnake on the ground
Common gartersnakes may have yellow, green, or blue stripes  (W.P. Leonard, Copyright)
Category: Reptiles
Family: Colubridae - Colubrids
Ecosystems: Riparian areas
If you see this species, please share your observation using the WDFW wildlife reporting form. Providing detailed information such as a photo and exact coordinates will improve the confidence and value of this observation to WDFW species conservation and management.

This is one of Washington’s most common snake species. No declines have been reported in the state but declines in amphibian populations could potentially result in declines of this species.

Reported declines in other states and Canadian provinces have been due to habitat loss and over-collecting for the pet and scientific trade.

According to NatureServe, the state conservation status of the common gartersnake population is considered “secure” in Washington. No declines have been reported in Washington. 

Description and Range

Physical description

Washington’s three gartersnake species (common, northwestern and terrestrial) are similar in general appearance and have coloration and patterns that vary regionally and by individual. All traits, especially scale counts, color and pattern, must be examined to correctly identify a garter snake to species. Although little appreciated, these are beautiful snakes with many stunning color variations.

The common gartersnake is a medium-sized dark snake with stripes. It has a dorsal pattern that is the most variable of any of the gartersnake species (Thamnophis species). Typically, three stripes are present; a thin dorsal (topside) stripe on the middle of the back and two thin lateral (side) stripes on the second and third dorsal scale rows. The lateral or dorsal stripes may be absent in some individuals. Adults can reach 54 inches total length but individuals in Washington are shorter. The pupil is round. The scales are keeled.

Differences in scale counts are important for distinguishing the three garter snakes in Washington. Common gartersnakes usually have 19 scales at mid-body, 7 upper labial scales and 10 lower labial scales. Occasionally, extra labial scales are present.

Eastern Washington


In eastern Washington, common gartersnakes are black bodied with bright yellow dorsal and lateral stripes. Distinct red blotches are present on the sides of the body just above the lateral stripes. A red cheek blotch is usually present. The ventral coloration is yellow or buff. Individuals, in some areas, may have blue or turquoise lateral stripes instead of yellow and these snakes usually have blue ventral scales.

Desert striped whipsnakes may be confused with gartersnakes. They differ in having smooth scales, 15 dorsal scale rows, and a mid-dorsal area that is dark brown or black with multiple white or yellow stripes on the sides of the body.

Western Washington


In western Washington, red blotches may or may not be present on the common gartersnake and the stripe coloration is much more variable.

Ground color is slate gray or black, sometimes with a bluish tinge. Stripe colors are yellow, green, turquoise or blue. All stripes may be the same color, or the lateral stripes may differ from the dorsal stripe in color. The ventral (underside) coloration is usually yellow or cream under the chin with increasing black pigmentation toward the tail. Snakes with blue lateral stripes usually have blue ventral coloration.

Snakes without red blotches have white patches of skin between the scales on the sides of the body. This trait will not be obvious in most snakes without gently stretching the skin to separate the scales above the lateral stripes. This trait is usually more prominent near the head. Other variations include orange blotches instead of red; blotches only on the anterior portions of the snake; or red blotches that are hidden under dark scales. In very melanistic (dark pigmented) individuals, all the skin between the scales is black and no white or red blotches are present.

In western Washington, northwestern gartersnakes and common gartersnakes are the most difficult species to distinguish based on coloration. Dark-bodied northwestern gartersnakes with green, turquoise, blue or yellow stripes are common. The scale counts differ; northwestern gartersnakes have 17 scales at mid-body (occasionally 19), 7 upper labial scales, and 8 or 9 lower labials.

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This short video highlights gartersnakes of Washington.

For more details about common gartersnake, see the Washington Herp Atlas.

Ecology and life history

In Washington, common gartesnakes are almost always found near water. Typical aquatic habitats include wetlands, bogs, ponds, lakes, springs, creeks, and rivers. They are good swimmers and can hunt both on and below the water surface. Juvenile common gartersnakes have been observed hunting newly metamorphosing pacific treefrogs in shallow, seasonal, water bodies.

Typical terrestrial habitats include sunny areas near water such as meadows, oak patches, forest openings, and shrubby areas. In the spring and fall snakes may be found away from water as they move to and from terrestrial overwintering sites.

Gartersnakes defend themselves by releasing the contents of their cloaca and musk glands then smearing this pungent foul-smelling mixture over themselves and their attacker. Some will also regurgitate the contents of their stomach and most will bite.

Common gartersnakes are one of the few vertebrates that can successfully prey on the extremely toxic rough-skinned newt. Research indicates that these snakes harbor significant amounts of active toxin in their tissues after consuming a newt. The amount of toxin in the liver varies depending on the number of newts eaten, but the amount in many cases is enough to severely incapacitate or kill avian predators and negatively affect mammalian predators.

At low elevations, activity starts in March and continues into early November. Snakes may remain in the vicinity of the overwintering site for two or more weeks until mating is complete and weather conditions are appropriate for dispersal. At low elevations in western Washington, snakes may be surface active in the vicinity of the overwintering site whenever site conditions warm over about 55° Fahrenheit.

The species breeds in spring after emergence. Males emerge before females and spend time on the surface near the overwintering sites. When a female emerges, the males will attempt to mate with her forming “mating balls” of many males around one female.

After mating, snakes disperse to summer foraging areas. In the lower Puget Sound area, female gartersnakes of all three species are commonly found clustered in open grassy areas. This behavior may be related to thermoregulation and gestation.

The young are born in late summer and early fall depending on location. In the lowland Puget Sound area, neonates start to appear in late August and early September.

Geographic range

The common gartersnake has the greatest geographical distribution of any gartersnake, occurring in all Washington Ecoregions. Occurrences are patchy in the central Columbia Basin.

Storm and Leonard 1995 provide detailed descriptions for each subspecies found in Washington: T.s. concinnus occurs in the Pacific Coast and southern Puget Trough ecoregions; T. s. fitchi occurs in eastern Washington ecoregions; and T.s. pickeringii occurs in the Puget Trough lowlands, primarily the Puget Trough ecoregion and portions of surrounding ecoregions.

This map from the Washington Herp Atlas illustrates the distribution of common gartersnake in Washington based on records in the WDFW database as of 2016. If you see this species in areas that are not indicated on the map or have more recent observations (less than 10 years), please share your observation using the WDFW wildlife reporting form

Common garter snake distribution map of Washington as of 2016: all counties but Benton and Franklin
Washington Herp Atlas (2017)

For a map of range-wide distribution and conservation status of this species, check out NatureServe Explorer and the International Union for Conservation of Nature Redlist

Regulations

Licenses and permits

Be advised that collection of this species is only permitted under a WDFW Scientific Collection Permit for research and educational activities.

Conservation

The state conservation status of the common gartersnake is “secure” based on the assumption that it is common according to the most current records.

Over hunting or collecting, wanton killing, and destruction of overwintering sites can result in local declines. Road mortality is also a threat in areas where snakes cross roads to access overwintering or foraging habitat.

Snake Fungal Disease (SFD) is a disease in snakes caused by the fungus Ophidiomyces ophiodiicola. To date, the fungus that causes this disease has not yet been found in Washington, however, there have been several reports of a fungal disease in gartersnakes that appears to be closely related to SFD. Find out more information here about SFD and what you can do to help.

Living with wildlife

Snakes are among the most misunderstood of all animals. Of the dozen or so species of snakes found in Washington, only the western rattlesnake is capable of inflicting a venomous bite, which it seldom does. All snakes are an important part of the natural food chain, eating a variety of prey—from mice and birds to frogs and insects.

Observe snakes, like all wild animals, from a respectful distance. Learn more about living with snakes.

Resources

References

Hallock, L. A. and W. P. Leonard. 1997. Inventory of the Ft. Lewis Military Reservation. Unpubl. Rep. Wash. Natural Heritage Program, Dept. of Natural Resources, Olympia. 52 pp. + appendices.

Rossman, D.A., N.B. Ford, and R.A. Seigel. 1996. The Garter Snakes: Evolution and Ecology. Animal Natural History Series. University of Oklahoma Press, Norman Oklahoma. 332 pp.

Storm, R.M. and W. P. Leonard (Coordinating Editors). 1995. Reptiles of Washington and Oregon. Seattle Audubon Society The Trailside Series, Seattle, Washington. 176 pp.

Williams, B.L., E.D. Brodie Jr., E.D. Brodie III. 2004. A resistant predator and its toxic prey: persistence of newt toxin leads to poisonous (not venomous) snakes. Journal of Chemical Ecology 30 (10): 1901-1919.

Personal communications 

William (Bill) Leonard, Washington Department of Transportation, Olympia, Washington.

WDFW publications

Washington Herp Atlas. 2009. A cooperative effort of Washington Natural Heritage Program, Washington Department of Fish and Wildlife, U.S.D.I. Bureau of Land Management, and U.S. Forest Service. Map products updated March 2017. Provisional PDF version of the website (2005-2019) created July 2019. 250 pp. 

WDFW educational resources

Other resources