Northwestern gartersnake (Thamnophis ordinoides)

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 northwestern gartersnake is a small to medium-sized, brown or black snake with stripes. The head is relatively small in proportion to the body. Spots may also be present. Typically, three stripes are present; a thin vertebral (back) stripe and two thin lateral (side) stripes. The vertebral and/or lateral stripes may be absent. Adults rarely exceed 23.6 inches total length. The pupil is round.

Coloration and patterns are highly variable. The dorsal (topside) color is brown, dark brown, slate gray or black. The vertebral stripe is white, yellow, orange, red, green, turquoise, or blue. The lateral stripes are white, yellow, green, turquoise, or blue. Small dark spots may be present between the vertebral stripe and the lateral stripes. White flecks are present on the edges of the dorsal scales. The ventral (underside) coloration is usually white or yellow at the chin with increasing bluish or black pigmentation toward the tail. Red-, orange- or salmon-colored blotches are usually present on the ventral surface of individuals with red vertebral stripes.

The following three variations are commonly seen in Washington: 1) A dark dorsal color with yellow, green, turquoise, or blue vertebral (back) and lateral (side) stripes; 2) A brown dorsal color with dull yellow vertebral and lateral stripes and two rows of alternating small dark spots above the lateral stripes and adjacent to the vertebral stripe; and 3) A dark dorsal color with a red vertebral stripe and bright yellow lateral stripes. In some individuals, the red pigment is only present in part of the vertebral stripe or appears more orange than red.

When northwestern gartersnakes have dark spots, the spots do not invade the dorsal stripe. Northwestern gartersnakes do not have red spots or bars along the sides of the body although some red pigmentation may be present along the sides of individuals with a red stripe. Northwestern gartersnakes have white specks on the edges of the dorsal scales, a trait our common gartersnakes do not have. In Washington, only northwestern gartersnakes will have a red vertebral stripe (locally called “red racers”), but this is one of the less common vertebral stripe color variations.

All three gartersnakes in Washington have scales that are keeled; differences in scale counts are important for distinguishing these snakes. Northwestern gartersnakes differ in having 17 scales (occasionally 19) rows at mid-body, the upper jaw has 7 upper labial scales, and 8 to 9 lower labial scales. Common gartersnakes usually have 19 scales at mid-body, 7 upper labial scales, and 10 lower labial scales, although occasionally, extra labial scales are present. Western gartersnakes usually have 19 or 21 rows at mid-body, 8 scales line the upper jaw (labial scales), and 10 scales line the lower jaw.

Desert striped whipsnakes may be confused with gartersnakes. They differ in being larger (adults greater than 3 feet 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.

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

This short video highlights gartersnakes of Washington.

Ecology and life history

Northwestern gartersnakes are the smallest and most terrestrial (land-based) of our three garter snake species. They occur in open grassy areas, in forest openings and edges of coniferous forest. They are also common near water bodies.

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.

At low elevations, activity starts in March and continues into early November. After emergence from winter dens, 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.

Northwestern gartersnakes typically breed in spring after emergence in late March to early April, and again in late September and early October.

After mating, snakes disperse to summer foraging areas. In the lower Puget Sound area, female garter snakes of all three species are commonly found clustered in open grassy areas.

Northwestern gartersnakes 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 (neonates) start to appear in late August and early September.

This species is a specialist on slugs and earthworms.

Geographic range

Northwestern gartersnakes occur primarily west of the Cascades Mountain crest in the Northwest Coast, Puget Trough and West Cascades ecoregions. Occurrences in the East Cascades Ecoregion are from the Cle Elum area in Kittitas County, northwestern Yakima County and western Klickitat County. The species may also cross into the Northern Cascade Ecoregion near Deming.

This map from the Washington Herp Atlas illustrates the distribution of northwestern 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. 

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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.