Thamnophis couchii - Sierra 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 - 38 inches long (46 - 96 cm). Neonates are 5 - 6.5 inches long (12.7 - 16.5 cm).

Appearance

A medium-sized slender snake with a head barely wider than the neck, a narrow snout, small eyes, and keeled dorsal scales. This snake is variable in appearance. The ground color is olive brown, dark brown, or blackish, and there are dark blotches on the back and upper sides which are obscured when the ground color is very dark. A light dorsal stripe may be present, but it is not distinct, except on the neck. LIght lateral stripes may or may not be present on the 2nd and 3rd scale rows. Northern populations of this snake have mottled black coloring below. This mottling is not present in southern populations.

Populations in streams draining into the Sacramento River all tend to lack lateral stripes. A melanistic population exists in Plum Creek, Tehama County.

Behavior

Active during daylight. A highly-aquatic snake - more likely than most garter snake species to be found in the water. Can also be found basking at the edge of water or lying on mats of floating vegetation.Can be active 10 months of the year at lower elevations, but as few as 3 - 3.5 months at very high elevations.
Forages for food in slow-moving water and usully drags its captures on to shore to eat. Able to crawl on stream bottoms. When threatened, this snake will often strike repeatedly and release cloacal contents.

Diet

Eats mainly fish and amphibians and their larvae, including frogs, tadpoles, and aquatic salamander larvae. Reproduction Poorly known. Young are born live, apparently in late July.

Range

According to Rossman, Ford, and Siegel, this snake ranges from the Pitt and Sacramento rivers south along the Sierra Nevada Mountains to the western end of the Tehachapi Mountains, with outlier populations along major rivers in west-central Nevada and the Owens Valley, at elevations from 300 - 8,000 ft. (91 - 2438 m).

Habitat

Associated with water - seasonal creeks, large mountain rivers, meadow ponds, and small lakes, in montane coniferous forests, oak woodlands, chaparral, pine juniper, and sagebrush. Prefers areas with rocks and vegetation.

Taxonomic Notes

According to Stebbins, T. couchi hybridizes with the Oregon Gartersnake -Thamnophis atratus hydrophilus, in the Pit River drainage and with the Two-striped Gartersnake -Thamnophis hammondii, at the western end of the Tehachapi Mountains.

T. couchii was formerly a composite of four species of gartersnakes: T. atratus, T. couchii, T. gigas, and T. hammondii, until 1987.

Conservation Issues (Conservation Status)

Not known to be threatened, but may be negatively impacted by competition with introduced bullfrogs and non-native fish in some areas.