Thamnophis sirtalis


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Thamnophis sirtalis
Species Authority: (Linnaeus, 1758)
Common Name(s):
English San Francisco Garter Snake

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2007
Date Assessed: 2007-03-03
Assessor(s): Frost, D.R., Hammerson, G.A. & Santos-Barrera, G.
Reviewer(s): Cox, N.A., Chanson, J.S. & Stuart, S.N.
Listed as Least Concern in view of its extremely wide distribution, presumed large population, and because populations are unlikely to be declining.
2007 Least Concern

Geographic Range [top]

Range Description:The species' wide range includes much of North America, from southeastern Alaska, British Columbia, southern Northwest Territories, northern Saskatchewan, central Manitoba, Ontario, central Quebec, and the Maritime Provinces of Canada, to southern California, central Utah, northeastern Colorado, New Mexico, and Chihuahua (Mexico) (disjunct), Texas, Gulf Coast, and southern Florida (Conant and Collins 1991, Ernst and Ernst 2003, Stebbins 2003). There is a very small population in northwestern Chihuaha, Mexico.
Canada; Mexico; United States
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: This species is represented by a very large number of occurrences (subpopulations) (Fitch 1980). Many occurrences have good viability. The total adult population size is unknown but probably exceeds 1,000,000. Long-term extent of occurrence, area of occupancy, number of subpopulations, and population size have probably been relatively stable. Currently, extent of occurrence, area of occupancy, number of subpopulations, and population size are probably relatively stable or declining at a low rate.
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: Throughout the range, this species inhabits a very wide range of aquatic, wetland, and upland habitats; habitat preference exhibits rather pronounced regional differences (e.g., east vs. west). When inactive, it occurs underground, in or under surface cover, or in other secluded sites.
Systems: Terrestrial; Freshwater

Threats [top]

Major Threat(s): No major threats have been identified. The Mexican population is vulnerable to changes in hydrology.

Conservation Actions [top]

Conservation Actions: Many occurrences of this species are in areas that afford adequate protection.

Bibliography [top]

Conant, R. and Collins, J.T. 1991. A Field Guide to Reptiles and Amphibians: Eastern and Central North America. Third Edition. Houghton Mifflin Company, Boston, Massachusetts.

Ernst, C.H. and Ernst, E.M. 2003. Snakes of the United States and Canada. Smithsonian Books, Washington, D.C.

Fitch, H.S. 1980. Thamnophis sirtalis. Catalogue of American Amphibians and Reptiles 270: 1-4.

IUCN. 2007. 2007 IUCN Red List of Threatened Species. Available at: (Accessed: 12th September 2007).

Rossman, D.A., Ford, N.B. and Seigel, R.A. 1996. The Garter Snakes. University of Oklahoma Press, Norman, Oklahoma and London, UK.

Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians. Third Edition. Houghton Mifflin Company, Boston, Massachusetts.

Citation: Frost, D.R., Hammerson, G.A. & Santos-Barrera, G. 2007. Thamnophis sirtalis. In: The IUCN Red List of Threatened Species. Version 2015.2. <>. Downloaded on 30 August 2015.
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