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Adult, Contra Costa County |
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Adult, Contra Costa County |
Adult in shallow water,
Contra Costa County |
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| Adult, Contra Costa County |
Juvenile, Contra Costa County |
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Adult, San Luis Obispo County
© Patrick Briggs |
Adult intergrade, Marin County |
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North of the San Francisco Bay, there is a very large intergrade range between T. a. hydrophilus and T. a. atratus or T. a. zaxanthus. The snakes in this area were formerly named T. a. aquaticus (or T. couchii aquaticus.) This subspecies is no longer recognized. More pictures and information about these intergrades can be found here.
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| Habitat, Contra Costa County |
Habitat, Contra Costa County |
Habitat, 500 ft, western
Stanislaus County |
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Description |
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 |
| Thamnophis atratus is 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, brown or black. There is distinct yellow or orange stripe on the back and a light stripe along the lower part of each side on the 2nd and 3rd scale rows. There may be small alternating dark spots on the sides, most noticable on juveniles. The throat is white or yellow, sometimes bright yellow. The underside is bluish or greenish sometimes with pink or yellow marks.
The following description is from Boundy, Jeff. Systematics of the Garter Snake Thamnophis atratus at the Southern End of Its Range. Proceedings of the California Academy of Sciences Volume 51, No. 6, p. 328. 1999.
"...midbody scale rows 19 (85%) or 17 (15%)... vertebral stripe relatively broad, averaging 3.2 (range 1.5 - 5.0) scale rows on the nape... vertebral stripe yellow to orange-yellow; lateral stripe conspicuous, pale green; dorsum dark gray to black; iris gray or brown; top of head dark, olive black, with a prominent parietal spot; supralabial suture marks narrow when present; demarcation between dorsal head color and pale supralabials distinct; chin cream, becoming bright yellow on the throat, grading to pale green in the thoracic region; ventral color darkening slightly posteriorly; midventral suffusion yellow to orange; dark markings absent from transverse ventral sutures; eye moderate in size..." |
| 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) but small fish are also eaten, and possibly small rodents. I have also seen this snake regurgitate two leeches. |
| Reproduction |
| Courtship has been observed during March and April. Young are born live late summer to early fall. |
| Range |
This subspecies is endemic to California.
According to Boundy, 1999, in his description of this snake, T. a. zaxanthus occurs in the "inner Coast Range from Napa and Solano to Santa Barbara counties and the Santa Lucia Range." This includes the East Bay south along the southern edge of the Santa Cruz Mountains where this subspecies interegrages with T. a. atratus. |
| Habitat |
| Creeks, streams, small lakes and ponds, in woodland, brush and forest and grassy ecotones. Seems to prefer shallow rocky creeks and streams. When found in muddy ponds there are usually rocky outcrops nearby. |
| Taxonomic Notes |
For a long time T. atratus was considered a subspecies of T. couchii. In 1987 it was classified as a distinct species. In 1999 Boundy revised the species to include T. a. zaxanthus.
North of the San Francisco Bay, there is a very large intergrade range between the T. a. hydrophilus and T. a. atratus or T. a. zaxanthus. The snakes in this area were formerly classified as T. a. aquaticus (previously T. couchii aquaticus.)
T. a. zaxanthus is still classified as T. a. atratus by some researchers. |
| Conservation Issues (Conservation Status) |
| Not known to be threatened, but gartersnakes have been negatively impacted by competition with introduced bullfrogs in some areas. |
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Taxonomy |
| Family |
Colubridae |
Colubrids |
| Genus |
Thamnophis |
North American Gartersnakes |
| Species |
atratus |
Aquatic Gartersnake |
Subspecies
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zaxanthus |
Diablo Range Gartersnake |
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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 zaxanthus - Boundy, 1999. Proc. California Acad. Sci. 51:328
from Original Description Citations for the Reptiles and Amphibians of North America © Ellin Beltz
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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
zaxanathus - Greek - za - good or intensive, and xanthus - yellow - refers to an "abundance of yellow on the dorsal pattern in contrast to other populations of T. atratus." Boundy, 2002 pers. comm.
from Scientific and Common Names of the Reptiles and Amphibians of North America - Explained © Ellin Beltz
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Alternate Names |
You will also find this snake classified asThamnophis atratus atratus - Santa Cruz Garter Snake in older texts and by those who do not recognize the validity of this subspecies.
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| Other California Gartersnakes |
T. a. atratus - Santa Cruz Gartersnake
T. a. hydrophilus - Oregon 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
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More Information and References |
Natureserve Explorer
California Dept. of Fish and Game
Boundy, Jeff. Systematics of the Garter Snake Thamnophis atratus at the Southern End of Its Range. Proceedings of the California Academy of Sciences Volume 51, No. 6, pp. 311-336. 1999.
Rossman, Douglas A., Neil B, Ford, & Richard A. Siegel. The Garter Snakes - Evolution and Ecology. University of Oklahoma press, 1996. Stebbins, Robert C. A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company, 2003.
Behler, John L., & F. Wayne King. The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, 1992.
Bartlett, R.D. , & Alan Tennant. Snakes of North America - Western Region. Gulf Publishing Co., 2000.
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.
Brown, Philip R. A Field Guide to Snakes of California. Gulf Publishing Co., 1997.
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The following status listings come from the Special Animals List which is published several times each year by the California Department of Fish and Game.
This snake is not included on the Special Animals List, which indicates that there are no significant conservation concerns for it in California.
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Organization
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Status Listing
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| U.S. Endangered Species Act (ESA) |
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| California Endangered Species Act (CESA) |
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| California Department of Fish and Game |
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| Bureau of Land Management |
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| USDA Forest Service |
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| Natureserve Global Conservation Status Ranks |
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World Conservation Union - IUCN Red List
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