Habitat, stream flowing from the eastern Sierras, 4,200 ft., Inyo County
Habitat, creek, 5,600 ft.
Habitat, mountain river, 2,600 ft.,
Habitat, mountain pond, 4,500 ft.,
Habitat, creek flowing from east side of the Sierra Nevada Mountains,
A Sierra Gartersnake crawls and swims in a Tuolumne County lake.
Not Dangerous (Non-poisonous) - This snake does not have venom that is dangerous to most humans.
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.
18 - 38 inches long (46 - 96 cm). Neonates are 5 - 6.5 inches long (12.7 - 16.5 cm).
A medium-sized slender snake with a head barely wider than the neck, a narrow snout, small eyes, and keeled dorsal scales.
Some average scale counts: Average of 8 upper labial scales, the 6th is wider than the 7th.
The rear pair of chin shields is longer than the front.
The internasals are longer than wide and pointed in front.
Average scale count at mid-body is 19 or 21.
Color and Pattern
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.
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 per year at very high elevations.
Able to crawl on stream bottoms.
When threatened, this snake will often strike repeatedly and release cloacal contents.
Diet and Feeding
Eats mainly fish and amphibians and their larvae, including frogs, tadpoles, and aquatic salamander larvae.
Sierra Gartersnakes have an immunity to newt toxins as they have been observed consuming juvenile Taricha torosa in Tulare and Calaveras Counties. (Herpetological Review 38(3), 2007)
Forages for food in slow-moving water and usully drags its captures on to shore to eat.
This species has been observed eating adult Pacific Newts (genus Taricha) which are deadly poisonous to most predators.
There is evidence * that when Common Gartersnakes (Thamnophis sirtalis) eat Rough-skinned Newts (Taricha granulosa) they retain the deadly neurotoxin found in the skin of the newts called tetrodotoxin for several weeks, making the snakes poisonous (not venomous) to predators (such as birds or mammals) that eat the snakes. Since California Newts (Taricha torosa) also contain tetrodotoxin in their skin, and since gartersnake species other than T. sirtalis also eat newts, it is not unreasonable to conclude that any gartersnake that eats either species of newt is poisonous to predators.
Not much is known about the breeding habits of this species.
Young are born live, apparently in late July.
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.
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.
(Rossman, Ford, and Siegel, 1996)
There is an old museum record from approximately 13 miles northwest of Red Bluff.
Stebbins and McGinnis, 2012, note that a population of gartersnakes at California City may also be this species.
Found at elevations from 300 - 8,000 ft. (91 - 2440 m) (Stebbins 2003)
(I have also received an undocumented report of a Sierra Gartersnake found at 8,200 ft.(2500 m) in the Desolation Wilderness, El Dorado County, where they might be found even higher in elevation.)
Notes on Taxonomy
According to Stebbins, 2013, 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.
1 Rossman, Douglas A., Neil B, Ford, & Richard A. Siegel. The Garter Snakes - Evolution and Ecology. University of Oklahoma press, 1996.
2Bartlett, R. D. & Patricia P. Bartlett. Guide and Reference to the Snakes of Western North America (North of Mexico) and Hawaii. University Press of Florida, 2009.
Bartlett, R. D. & Alan Tennant. Snakes of North America - Western Region. Gulf Publishing Co., 2000.
Brown, Philip R. A Field Guide to Snakes of California. Gulf Publishing Co., 1997.
Ernst, Carl H., Evelyn M. Ernst, & Robert M. Corker. Snakes of the United States and Canada. Smithsonian Institution Press, 2003.
Wright, Albert Hazen & Anna Allen Wright. Handbook of Snakes of the United States and Canada. Cornell University Press, 1957.
Samuel M. McGinnis and Robert C. Stebbins. Peterson Field Guide to Western Reptiles & Amphibians. 4th Edition. Houghton Mifflin Harcourt Publishing Company, 2018.
Stebbins, Robert C. A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company, 2003.
Behler, John L., and F. Wayne King. The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, 1992.
Powell, Robert., Joseph T. Collins, and Errol D. Hooper Jr. A Key to Amphibians and Reptiles of the Continental United States and Canada. The University Press of Kansas, 1998.
The following conservation status listings for this animal are taken from the October 2021 California "Special Animals List" and the October 2021 "State and Federally Listed Endangered and Threatened Animals of California" list, both of which are produced by multiple agencies and available here: https://www.wildlife.ca.gov/Data/CNDDB/Plants-and-Animals. You can check the link to see if there are more recent lists.
If no status is listed here, the animal is not included on either list. This most likely indicates that there are no serious conservation concerns for the animal. To find out more about an animal's status you can go to the NatureServe and IUCN websites to check their rankings.
This snake is not included on the Special Animals List, which indicates that there are no significant conservation concerns for it in California.