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A Guide to the Amphibians
and Reptiles of California


Oregon Gartersnake - Thamnophis atratus hydrophilus

Fitch, 1936
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Aquatic Gartersnake California Range MapRange in California: Orange

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Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake
  Adult 1, Mendocino County  
Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake
  Adult 2, Mendocino County  
Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake
  Adult 3, Mendocino County  
Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake
Juvenile, Mendocino County Adult without dorsal stripe, Del Norte County © Alan Barron

Juvenile, Mendocino County Adult, Mendocino County
Intergrades
Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade  
Adult intergrade, Marin County. Adult intergrade, Marin County. Adult intergrade, Marin County.  
North of the San Francisco Bay, there is a very large intergrade range between T. a. hydrophilus, T. a. atratus, and T. a. zaxanthus. The snakes in this area were formerly classified as T. a. aquaticus (previously T. couchii aquaticus.)
This subspecies is no longer recognized. More pictures and information about these intergrades can be seen here.

 
Feeding Behavior
Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake
An Oregon Gartersnake eating a fish in Trinity County. © Kevin Andras.
Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake
An Oregon Gartersnake eats a fish in Mendocino County. © Linda Bostwick Adult eating a trout, Shasta County
© Thomas Kavenaugh
    " We were just about to leave after lunch when I saw this guy slip into the water out of the corner of my eye. I started changing lenses knowing he would come up nearby as the pool was only 4 feet across. You can imagine my surprise to see him come up with this very angry trout. I took a number of shots as they fought. They were in still water about 4 inches down. They even went over a 2 foot waterfall but the snake never let go. Eventually he got his back end up on a rock, slowly dragged the fish out and eventually began swallowing it."
- Thomas Kavenaugh
Oregon Gartersnake Oregon Gartersnake Oregon Gartersnake  
Oregon Gartersnake eating a neotenic Coastal Giant Salamander, Dicamptodon tenebrosus, in Trinity County. © Ben Witzke

 
Habitat
Oregon Gartersnake Habitat Oregon Gartersnake Habitat Oregon Gartersnake Habitat  
Habitat, Mendocino County Habitat, Mendocino County. These small pools of water along the edge of a wide riverbank in summer, contained Foothill Yellow-legged Frogs and tadpoles, Bullfrogs, and Oregon Gartersnakes. Habitat, Mendocino County  

More pictures of this animal and its natural habitat are available on our Northwest Herps page.

Short Video
  Oregon Gartersnake  
  An Oregon Gartersnake basks on a rock in a
River in Mendocino County, and swims away.
 
Description

Not Dangerous to 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.
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.

Some average scale counts: Average of 8 upper labial scales, 6 and 7 not enlarged. 11 lower labial scales. Rear pair of chin shields is longer than the front. The internasals are longer than they are wide and pointed in front. Average of 19 or 21 scales at mid-b
Key to Identifying California Gartersnake Species
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.
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.

Taxonomy
Family Colubridae Colubrids Oppel, 1811
Genus Thamnophis North American Gartersnakes Fitzinger, 1843
Species atratus Aquatic Gartersnake (Kennicott, 1860)
Subspecies


hydrophilus Oregon Gartersnake Fitch, 1936
Original Description
Thamnophis atratus - (Kennicott, 1860) - in Cooper, Expl. Surv. R.R. Miss. Pacific, Vol. 12, Book 2, Pt. 3, No. 4, p. 296
Thamnophis atratus hydrophilus - Fitch, 1936 - Amer. Midland Nat., Vol. 17, p. 648

from Original Description Citations for the Reptiles and Amphibians of North America © Ellin Beltz

Meaning of the Scientific Name
Thamnophis - Greek - thamnos - shrub or bush, and ophis - snake, serpent
atratus
- Latin - clothed in black, mourning - refers to the dark dorsal color
hydrophilus - Greek - hydor - water, and philus - loving - refers to the snakes aquatic proclivities

from Scientific and Common Names of the Reptiles and Amphibians of North America - Explained © Ellin Beltz

Alternate Names
Formerly T. couchii hydrophilus
Oregon Aquatic Garter Snake

Other California Gartersnakes
T. a. atratus - Santa Cruz Gartersnake
T. a. zaxanthus - Diablo Range Gartersnake
T. couchii - Sierra Gartersnake
T. gigas - Giant Gartersnake
T. e. elegans - Mountain Gartersnake
T. e. terrestris - Coast Gartersnake
T. e. vagrans - Wandering Gartersnake
T. hammondii - Two-striped Gartersnake
T. m. marcianus - Marcy's Checkered Gartersnake
T. ordinoides - Northwestern Gartersnake
T. s. fitchi - Valley Gartersnake
T. s. infernalis - California Red-sided Gartersnake
T. s. tetrataenia - San Francisco Gartersnake

More Information and References
California Department of Fish and Wildlife

Stebbins, Robert C., and McGinnis, Samuel M.  Field Guide to Amphibians and Reptiles of California: Revised Edition (California Natural History Guides) University of California Press, 2012.

Stebbins, Robert C. California Amphibians and Reptiles. The University of California Press, 1972.

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.

Bartlett, 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.

Rossman, Douglas A., Neil B, Ford, & Richard A. Siegel. The Garter Snakes - Evolution and Ecology. University of Oklahoma press, 1996.

Conservation Status

The following status listings come from the Special Animals List and the Endangered and Threatened Animals List which are published by the California Department of Fish and Wildlife.


This snake is not included on the Special Animals List, which indicates that there are no significant conservation concerns for it in California.

Organization
Status Listing
U.S. Endangered Species Act (ESA) None
California Endangered Species Act (CESA) None
California Department of Fish and Wildlife None
Bureau of Land Management None
USDA Forest Service None

 

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