A Guide to the Amphibians
and Reptiles of California

Two-striped Gartersnake - Thamnophis hammondii

(Kennicott, 1860)

Click on a picture for a larger view

Range in California: Red

Key to Identifying
California Gartersnakes

Range Maps of
California Gartersnakes

Baja California

Sub-adult, San Diego County

Adult, Santa Barbara County
© Brian Hubbs

Sub-adult, San Diego County

Sub-adult in defensive pose, San Diego County. This snake has flattened its head into a triangular shape to mimic a venomous snake to scare me away.

Adult, Santa Barbara County
© Ryan Sikola

Adult, preparing to shed, coastal San Diego County

Adult, San Diego County © Taylor Henry

Adult, Laguna Mountains,
San Diego County © John Stoklosa

Adult, Ventura County
© Jeremy Huff

Sub-adults, two color phases,
Ventura County. © Brian Hubbs

Adult, Santa Barbara County
© Jason Butler

An adult snake with a reddish stripe from just west of the Piru River in Ventura County. © Vince Semonsen

Adult, San Bernardino County © Jeff Ahrens

Adult from the Mohave Desert at Victorville,
San Bernardino County © Michael Clarkson

Adult, Ventura County
© Patrick Briggs

Adult, preparing to shed, with milky eyes,
San Diego County

Adult in creek, Orange County
© Jeff Ahrens

Adult swimming in a flooded meadow in in the San Diego County mountains
© Cherie Trivizo

Adult, Riverside County
© Jeff Ahrens

Adult in creek, San Bernardino County © Jeff Ahrens

Adult in an Orange County creek © Robert Hamilton

Adults, Santa Ana Mountains,
Orange County © Tadd Kraft

Adult, San Diego County
© Paul Maier

The Two-striped Gartersnake typically has a single light stripe low on each side of the body but lacks the light stripe on top of the back which is present in most other gartersnakes found in California.

Sign, San Diego County park

Central Coast Dark Morph Two-striped Gartersnakes, and Others with Aberrant Pigmentation or Unusual Patterns

Melanistic adult, San Luis Obispo County © Katie Drexhage

Very dark adult, Monterey County © Harry Moffett

A very dark adult from the San Gabriel Mountains in San Bernardino County © Kyle Watson This snake has defensively flattened its head into a triangular shape to make it appear to be venomous.

Melanistic adult, San Luis Obispo County © Ryan Sikola

An atypical spotted morph adult from Los Angeles County © Chris DeGroof

This unusually-pigmented spotted morph Two-striped Gartersnake was found in Riverside County. It's not an albino, because the eyes are dark, but it is missing some of its normal dark pigment. © ELMT Consulting, Inc. Travis J. McGill
This snake has defensively flattened its head into a triangular shape to make it appear to be venomous.

This melanistic adult Two-striped Gartersnake was observed in San Luis Obispo County. © Ryan Sikola

Juvenile, San Luis Obispo County.
Juvenile melanistic snakes in this area start out lighter in color with a light belly then get darker with age.
© Ryan Sikola

Hybrids

Adult, Santa Barbara County
© Ryan Sikola

Adult, San Luis Obispo County
© Ryan Sikola

These snake are unusual hybrids of the Two-striped Gartersnake and the Diablo Range Gartersnake, Thamnopis atratus zaxanthus. Note the thin yellow vertebral stripe that is not present on T. hammondii and is much thinner than that found on T. atratus. T. atratus is so scarce at the edge of its range in San Luis Obispo and Santa Barbara counties that they breed with T. hammondii which is more abundant in the area.

Two-striped Gartersnakes Feeding and Predation

Steve Ivie and his Cub Scout troupe saw this gartersnake enter a river in the San Gabriel Mountains of Los Angeles County. They watched the snake swim upstream and grab a trout about 8 or 9 inches in length, then drag the trout onto a rock at the edge of the river, and eat it, as you can see above. © Steve Ivie

Adult eating a sucker on a rock next to the San Gabriel River, Los Angeles County. © Seth Coffman

This juvenile snake is eating a Baja California Treefrog tadpole in the
Santa Monica Mountains of Los Angeles County. © NPS

This juvenile snake is eating a young California Treefrog in the Santa Monica Mountains of Los Angeles County. © NPS

Adult spotted morph T. hammondii eating a trout pulled from a pool in a Monterey County
creek that dried up during the summer of 2014 due to the drought. © Pete Veilleux

This dead Two-striped Gartersnake was found in San Diego County inside the belly of an American Bullfrog along with an Arroyo Toad which was alive. When put back in the creek, the toad hopped away. © Andrew Borcher
Animals captured and handled under authorization by the Califoirnia Department of Fish and Wildlife.

This adult Two-striped Gartersnake was observed eating a California Toad in San Diego County. It took the snake almost 45 minutes to completely swallow the toad, which had puffed its body up to make itself harder to swallow. You can also watch a YouTube video of the event:Two Striped Garter Feeds on a California Toad
© Douglas S. Brown

Habitat

Habitat, coastal sage,
San Diego County

Habitat, desert creek,
San Diego County

Habitat, flooded meadow in Spring, San Diego County mountains
© Cherie Trivizo

Habitat, San Diego County
mountain meadow

Habitat, coastal stream,
San Diego County

Habitat, San Gabriel Mountains,
Los Angeles County

Habitat, creek, 5,200 ft., San Gabriel Mountains, Los Angeles County

Habitat, small creek, Orange County
© Jeff Ahrens

Habitat, lake edge, 4,600 ft.
San Diego County

Habitat, mountain creek,
San Diego County

Habitat, seasonal pond,
San Diego County

Habitat, small creek,
San Diego County

Short Video

A Two-striped Gartersnake
filmed in San Diego County.

Description

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.

Size

24 - 40 inches long (61 - 102 cm). Most often 18 - 30 inches long (46 - 76 cm).
Neonates are 7.5 - 9 inches (19 - 23 cm).

Appearance

A medium-sized snake with a head barely wider than the neck and keeled dorsal scales.

Color and Pattern

Appearance is variable - there are two basic pattern morphs - striped, and spotted.
Both have a drab olive, brown, or dark gray ground color, with no dorsal stripe, except for a partial stripe on the neck.

The striped morph has a yellowish to gray lateral stripe on each side, and a fairly uniform dorsal coloring, with only faint spotting.

The spotted morph has two rows of small dark spots on each side and lateral stripes are often not present.
Light areas between the scales between the rows of dark spots can create a checkered appearance.

The underside is pale yellow or orange, unmarked, or with dark smudging.

"Black individuals, sometimes with obscure or without laterals sripes, or even spots..." are found along the outer coast in San Luis Obispo County, and can be expected from Monterey Bay to Santa Barbara County. (Stebbins, 2003)

A dark green and a reddish color morph occur along the Piru River in Ventura County. (Stebbins, 2003)

A melanistic population occurs on Catalina Island.

Key to Identifying California Gartersnake Species

Life History and Behavior

Primarily aquatic.
Diurnal.
Also active at night and at dusk during hot weather in some areas.
Can be active most of the year depending on weather conditions. Has been found from January to November.

Defense

Like most gartersnakes, when picked up, will often strike repeatedly and release cloacal contents and musk.
When threatened, some Two-striped Gartersnakes assume a defensive pose with the head flattened into a triangular shape that makes it look like the head of a venomous snake, such as a rattlesnake, to scare away the threat.

Diet and Feeding

Eats fish, fish eggs, tadpoles, newt larvae, small frogs and toads, leeches, and earthworms.

Garden Slender Salamanders - Batrachoseps major (and their detached tails) and aquatic leeches hava also been found in the stomach contents of T. hammondii. (Edward L. Irvin, et al. Herpetological Review 34)1), 2003.

Forages for food in and under water.

An adult T. hammondii was observed in an underwater ambush position about 15 cm below the surface, compressing its body into side-by-side loops while using its tail to anchor itself in stable aquatic vegetation. From this position it periodically quickly lunged forward at its prey. (Edward L. Ervin and Robert N. Fisher, Herpetological Review 38(3), 2007.

Reproduction

Mating has been observed in late March and early April. An average litter of about 15 live young are born from July to October.
Females are known to store sperm for later use.

Habitat

Among the most aquatic of the gartersnakes. Generally found near water sources - pools, creeks, cattle tanks, and others, often in rocky areas. Associated vegetation: oak woodland, willow, coastal sage scrub, scrub oak, sparse pine, chaparral, and brushland.

Geographical Range

Ranges continuously from near Salinas in Monterey County south along the coast mostly west of the south Coast Ranges, to southern California where it ranges east through the Transverse Ranges, and south through the coastal area and the Peninsular Ranges into northern Baja California. Occurs in some perennial desert slope streams north of the Transverse Ranges and east of the Peninsular Ranges, and into the Mohave Desert in Victorville. Also occurs on Catalina Island.

Occurs along the western part of northern Baja California, and in parts of Baja California Sur.

Elevational Range

At elevations from sea Level to 6,988 ft. (2130 m).

Notes on Taxonomy

Formerly classified as a subspecies of Thamnophis couchii.
T. digueti was synonymized with T. hammondii by McGuire and Grismer (1993, Herpetologica 49:354-365).

The Santa Catalina population of T. hammondii has been treated as a distinct subspecies by the California Dept. of Fish and Game - Santa Catalina garter snake, Thamnophis hammondii ssp.

Alternate and Previous Names (Synonyms)

Thamnophis hammondii - Two-striped Garter Snake (Stebbins 1985, 2003, 2012)
Thamnophis couchi hammondii - Two-striped Garter Snake (Stebbins 1966)
Thamnophis elegans hammondii (Stebbins 1954)
Thamnophis elegans hammondii - Southern California garter snake (Klauber 1934)
California garter snake (Van Denburgh 1897)
Thamnophis hammondii - (Kennicott, 1860)
Hammond's garter snake;
Pacific garter snake;
Water snake

Conservation Issues (Conservation Status)

Designated a California Species of Special Concern and protected by the state.

Loss of wetland habitats have contributed to a reduction in the range of this snake.

Declines in population of the species have been attributed to human impacts, including urban development and flood control in the southern part of its range, and habitat modification by livestock, drought, loss of native prey and predation by alien species in its northern range.
(Jennings and Hayes 1994)

"...restoration of aquatic habitat and supplementation with artificial wetlands should be explored as a management option in extirpated sites." Terrestrial habitat surrounding the aquatic habitats, especially rodent burrows, are utilized for overwintering and should also be protected.
(Thomson, Wright, and Shaffer, 2016)

Taxonomy
Family	Colubridae	Colubrids	Oppel, 1811
Genus	Thamnophis	North American Gartersnakes	Fitzinger, 1843
Species	hammondii	Two-striped Gartersnake	(Kennicott, 1860 )
Original Description
Thamnophis hammondii - (Kennicott, 1860) - Proc. Acad. Nat. Sci. Philadelphia, Vol. 12, p. 332 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 hammondii - honors Hammond, William A. from Scientific and Common Names of the Reptiles and Amphibians of North America - Explained © Ellin Beltz
Alternate Names
None
Other California Gartersnakes
T. a. atratus - Santa Cruz Gartersnake T. a. hydrophilus - Oregon 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. 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 Rossman, Douglas A., Neil B, Ford, & Richard A. Siegel. The Garter Snakes - Evolution and Ecology. University of Oklahoma press, 1996. Robert C. Thomson, Amber N. Wright, and H. Bradley Shaffer. California Amphibian and Reptile Species of Special Concern. University of California Press, 2016. Mark R. Jennings and Marc P. Hayes. Amphibian and Reptile Species of Special Concern in California. Report to California Department of Fish and Game. 1994. 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. 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. 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, 1957.

Conservation Status

The following conservation status listings for this animal are taken from the November 2020 California "Special Animals List" and the November 2020 "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.

The 2019 Special Animals List lists the population on Santa Catalina Island as a separate subspecies, Thamnophis hammondii pop. 1. - Santa Catalina gartersnake. This listing for this snake is shown below the listings for the other populations of T. hammondii.

This is the listing for Thamnophis hammondii - two-striped gartersnake:

Organization

Status Listing

Notes

NatureServe Global Ranking

Apparently Secure—Uncommon but not rare; some cause for long-term concern due to declines or other factors.

NatureServe State Ranking

S3S4

Vulnerable—Vulnerable in the state due to a restricted range, relatively few populations (often 80 or fewer), recent and widespread declines, or other factors making it vulnerable to extirpation from the state.

Apparently Secure—Uncommon but not rare in the state; some cause for long-term concern due to declines or other factors.

U.S. Endangered Species Act (ESA)

None

California Endangered Species Act (CESA)

None

California Department of Fish and Wildlife

SSC

Species of Special Concern

Bureau of Land Management

Sensitive

USDA Forest Service

Sensitive

IUCN

Least Concern

This is the listing for Thamnophis hammondii pop.1 - Santa Catalina gartersnake:
Organization	Status Listing	Notes
NatureServe Global Ranking	G4T1?	The species is: Apparently Secure—Uncommon but not rare; some cause for long-term concern due to declines or other factors. This subspecies is: Critically Imperiled—At very high risk of extinction due to extreme rarity (often 5 or fewer populations), very steep declines, or other factors. Imperiled—At high risk of extinction due to very restricted range, very few populations (often 20 or fewer), steep declines, or other factors.
NatureServe State Ranking	S1	Critically imperiled in the state because of extreme rarity (often 5 or fewer populations) orbecause of factor(s) such as very steep declines making it especially vulnerable to extirpation from the state.
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
IUCN	None

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