Western Terrestrial Garter Snake

Contents:
 
Links:
Taxon, Status, and Ranks Habitat Photos
General Description State Status Comments
Identification Tips Inventory & Research Needs Key Features
Phenology Threats & Mgmt Concerns
Range References Distribution Map

Taxon, Status, and Rank

Species Thamnophis elegans     (Baird and Girard, 1853)
Family Colubridae
(Colubrids)
Status none
State Rank S5
Global Rank G5

Washington’s three garter snake species are similar in appearance and have coloration and patterns that vary regionally and by individual. Correct identification requires consideration of all traits including scale counts, color and pattern. Although little appreciated, these are beautiful snakes with many stunning color variations.

General Description

This is a medium-sized gray to brown snake with stripes and small spots. Typically three stripes are present: a thin vertebral stripe and two thin lateral stripes. The stripes are yellow or cream colored. The lateral stripes are on the 2nd and 3rd scale rows. The small dark spots occur in two alternating rows between the vertebral stripe and lateral stripes. The upper spots invade the vertebral stripe. The belly is gray with black pigment concentrated along the mid-belly. The subspecies (T.e. vagrans) that occurs in Washington grows to 97 cm (38 in) total length. The pupil is round. The scales are keeled and there are usually 19 or 21 rows at mid-body, 8 scales line the upper jaw (labial scales) and 10 scales line the lower jaw.

Variation: The mid-dorsal stripe may be indistinct, absent or incomplete in some individuals. The lateral stripes may be indistinct. Some individuals appear more spotted than striped. Melanistic forms have been observed in Washington. Coloration of this species in the Columbia Basin tends to be rather dull in comparison with populations in western Washington. See Photos Page.

Identification Tips

Differences in scale counts are important for distinguishing the garter snakes. Western Terrestrial Snakes typically have 19 or 21 scales at mid-body, 8 upper labial scales and 10 lower labial scales.

In Western Washington, spotted forms of the Northwestern Garter Snake look similar to Western Terrestrial Garter Snake. The scale counts differ with the Northwestern Garter Snake having 17 scales at mid-body (occasionally 19), 7 upper labial scales and 8 or 9 lower labials. Also, the dorsal spots do not invade the vertebral stripe. Overall, the Northwestern Garter Snake is a smaller snake and has a relatively small head.

In Washington, Common Garter Snakes have 7 upper labials and no dark spotting on the dorsal surface. Throughout eastern Washington and parts of western Washington, the Common Garter Snake has red blotches on the sides of the body above the lateral stripe. In the Puget Sound area, where Common Garter Snakes lack red side blotches, they usually have white blotches on the skin between the scales above the lateral stripes. It may be necessary to separate the scales to see this trait.

Striped Whipsnakes differ in being larger (adults greater than 1 meter in length), having smooth scales, 15 dorsal scale rows and they have a distinct pattern of dark and light colored stripes on the sides of the body. See Key Features Page.

Phenology

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.

Breeding takes place in spring after emergence in late March to early April. Fall courtship activities have been observed in early September in British Columbia. After mating, snakes disperse to summer foraging areas. Migrations of up to 3 km have been documented. Once snakes reach their foraging areas, movement distances decline again.

In the lower Puget Sound area, female garter snakes of all three species are commonly found clustered in open grassy areas near water bodies. Aggregations of as many as 20 individual gravid female Western Terrestrial Garter Snakes have been observed in other parts of the range. Western Terrestrial Garter Snakes give birth to their young rather than lay eggs; the young are born in late summer and early fall depending on location. In the lowland Puget Sound area, newborns start to appear in late August and early September. Starting in September, the snakes migrate back to their overwintering locations.

Range

Western Terrestrial Garter Snakes have been documented in all Washington ecoregions. Occurrences in the Northwest Coast, West Cascades and North Cascades ecoregions are uncommon.

Only one occurrence has been documented in the North Cascades Ecoregion. Collected in 1920, this specimen is in the US National Museum collection. Because of the convoluted taxonomic history of T. elegans, this specimen should be examined to verify that is not the Northwestern Garter Snake (T. ordinoides). See Distribution Map.

For information on the complete range of this species, see NatureServe Explorer.

Habitat and Habits

Contrary to their name, Western Terrestrial Garter Snakes are almost always found near water in Washington. This is especially true in the Columbia Basin where populations are restricted to aquatic areas due to the xeric conditions of the uplands. These snakes have been observed along ponds, wetlands, lakes, stream edges, irrigation canals and rivers. Typically, they are found in grassy or shrubby areas on the edges of water bodies or in meadows and other openings nearby. Overwintering locations are terrestrial and can be far from foraging habitats. Many individuals use the same overwintering location. Overwinter habitats include rocky talus slopes, fractured bedrock, rock piles and roadsides.

Garter snakes 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 content of their stomach and most will bite. This can make handling garter snakes somewhat unpleasant.

Western Terrestrial Garter Snakes have toxic salivary secretions that may help immobilize prey. People have reported localized swelling from bites. These reports are infrequent and the toxins are not thought to be a serious problem for humans.

State Status Comments

This is a wide ranging and common snake species associated with water. No declines have been reported in Washington at this time.

Inventory and Research Needs

Observations can be submitted to the Washington Department of Fish and Wildlife WSDM database by contacting Lori Salzer by E-mail salzeljs@dfw.wa.gov. Of particular interest are observations from the Northwest Coast, West Cascades and North Cascades ecoregions. Photograph vouchers should include photographs of 1) the head showing the labial scales, 2) the dorsal surface, and 3) the ventral surface.

Threats and Management Concerns

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 the snakes must cross to access overwintering or foraging habitat.

References

Jansen (1987). Nussbaum, et al. (1983); Rossman et al. (1996); Stebbins (2003); Storm & Leonard (1995)



Hallock, L.A. and McAllister, K.R. 2009. Western Terrestrial Garter Snake. Washington Herp Atlas. http://www1.dnr.wa.gov/nhp/refdesk/herp/

Last updated: June 2009


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