Thamnophis atratus hydrophilus - Oregon Gartersnake

Nonvenomous

Gartersnakes have toxins in their saliva which can be deadly to their prey and their bite might produce an unpleasant reaction in humans, but they are not considered dangerous to humans.

Size

18 - 40 inches long (46 - 102 cm). Most snakes encountered are generally 18 - 28 inches long (46 - 71 cm). Neonates are 7 - 10 inches ( 18 - 25 cm).

Appearance

A medium-sized slender snake with a head barely wider than the neck and keeled dorsal scales. Ground color is gray, olive-gray, or brownish. This snake may have a light stripe on the back and a light stripe along the lower part of each side. The dorsal stripe and the side stripes may be absent or obscured, not contrasting sharply with the ground color, leaving a checkered appearance instead of striped. There are usually alternating dark spots on the sides. The throat is light. The underside is light and unmarked with a pinkish or purplish tint toward the tail.

Behavior

A highly-aquatic snake, able to remain underwater, but also found away from water. Active during the day, and after dark during very hot weather. Can be active most of the year when conditions allow, but primarily found spring through fall.

When threatened, this snake will often escape into water, hiding on the bottom. If it is frightened when picked up, it will often strike repeatedly and release feces from the cloaca and expel musk from anal glands.

Adults have been found to forage actively, neonates are sit-and-wait foragers, and juveniles practice both forms of foraging.

Diet

Probably eats mainly amphibians and their larvae, including frogs, tadpoles, and aquatic salamander larvae (newts and giant salamanders, Taricha and Dicamptodon ), but small fish are also eaten. Captives have also taken small rodents.

Reproduction

Courtship has been observed during March and April. Young are born live late summer to early fall.

Range

This subspecies, Thamnophis atratus hydrophilis - Oregon Gartersnake, ranges from northern Sonoma County north along the coast to Douglas County, Oregon, and east throughout the north coast ranges and to the lower Pit River area. It is absent from much of the coast around Humboldt County.

The species Thamnophis atratus - Aquatic Gartersnake, ranges from Santa Barbara County north through the coast ranges into southwest Oregon, including most of the state north of Santa Barbara County and west of the interior valleys.

Habitat

Creeks, streams, rivers, small lakes and ponds, in woodland, brush and forest. Seems to prefer shallow rocky creeks and streams.

Taxonomic Notes

This snake is known to hybridize with T. couchii in Shasta County. For a long time T. atratus was considered a subspecies of T. couchii. In 1987 it was classified as a distinct species.

North of the San Francisco Bay, there is a very large intergrade range between the Oregon Gartersnake and T. a. atratus or T. a. zaxanthus. The snakes in this area were formerly classified as T. a. aquaticus (previously T. couchii aquaticus.)

Conservation Issues (Conservation Status)

Not known to be threatened, but gartersnakes have been negatively impacted by competition with introduced bullfrogs in some areas.