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A Guide to the Amphibians
and Reptiles of California


Santa Cruz Gartersnake - Thamnophis atratus atratus

(Kennicott, 1860)
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Aquatic Gartersnake California Range MapRange in California: Red & Gray

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to the other subspecies.


observation link





Santa Cruz Gartersnake
Adult, San Mateo County © Bob Cossins
Santa Cruz Gartersnake Santa Cruz Gartersnake Santa Cruz Gartersnake Santa Cruz Gartersnake
Adult, Santa Cruz Mountains, Santa Cruz County. Adult, San Mateo County
© Chad M. Lane
Adult, Santa Cruz County © Zachary Lim
Santa Cruz Gartersnake Santa Cruz Gartersnake Santa Cruz Gartersnake Santa Cruz Gartersnake
Juvenile, Santa Cruz County Adult, Santa Cruz County
© Brad Alexander
Santa Cruz Gartersnake Santa Cruz Gartersnake Santa Cruz Gartersnake Santa Cruz Gartersnake
Adult, San Mateo County. © Richard Porter Adult, Santa Cruz County © Scott Peden
Santa Cruz Gartersnake Santa Cruz Gartersnake Santa Cruz Gartersnake Valley Gartersnake
Adult, Santa Cruz County
© John Sullivan
Adult, San Mateo County © Bob Cossins Adult, Santa Clara County © Luke Talltree Three species found at the same Marin County location, including Thamnophis atratus, and Thamnophis elegans.
© Luke Talltree
Santa Cruz Gartersnake      
Adult, Santa Clara County © Jared Heald      
       
Feeding
Santa Cruz Gartersnake Santa Cruz Gartersnake    
Two views of a Santa Cruz Gartersnake eating a newt
(either Taricha torosa or Taricha granulosa) in Santa Clara County
© Odophile.com
   
     
Breeding Behavior
Santa Cruz Gartersnakes Santa Cruz Gartersnakes Santa Cruz Gartersnakes Santa Cruz Gartersnake
A group of breeding Santa Cruz Gartersnakes photographed in late March in San Mateo County.
Snakes were moving constantly in the reeds and across trails heading towards the reeds. They're not easy to see, but if you look carefully at the enlarged images, you can see several snakes in various areas of each picture. © Zachary Lim
This one was picked up and photographed as it was heading into the reeds. © Zachary Lim
   
Intergrades
Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade
Adult intergrade, Marin County. Adult intergrade, Marin County. Adult intergrade, Marin County. Adult from Marin County Headlands, just northwest of the Golden Gate Bridge
© Zach Lim
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.
   
Habitat
Santa Cruz Gartersnake Habitat Santa Cruz Gartersnake Habitat Santa Cruz Gartersnake Habitat Santa Cruz Gartersnake Habitat
Habitat, Santa Cruz County
Habitat, Santa Clara County Habitat, Santa Clara County Habitat, San Mateo County
Santa Cruz Gartersnake Habitat Santa Cruz Gartersnake Habitat Santa Cruz Gartersnake Habitat Santa Cruz Gartersnake Habitat
Habitat, San Mateo County Habitat, San Mateo County Habitat, San Mateo County Habitat, San Mateo County
     
Habitat, Santa Cruz Mountains
© Zachary Lim
     
       
Short Video
Santa Cruz Gartersnake  
A feisty juvenile Santa Cruz Gartersnake in the Santa Cruz Mountains.      
     
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
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.

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-body.

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. 330. 1999.

"...midbody scale rows 19 (65%) or 17 (35%) ... vertebral stripe yellow to orange yellow and broad, averaging 4.0 (range 2.7 - 6.5) scale rows in the nuchal area ... lateral stripes absent; dorsum olive black, grading to dark olive at the ventrals; dorsal black spots obscure; iris dark brown; top of head dark olive brown to olive black, with a prominent parietal spot; supralabial suture marks narrow when present; demarcation between dorsal head color and dusky olive supralabials indistinct; chin cream, becoming deep yellow on the throat; venter abruptly becoming olive gray in the thoracic area, continuously darkening posteriorly; prominent yellow-orange midventral suffusion; dark markings absent from transverse ventral sutures..."

Color and Pattern
Ground color is gray, brown or black.
There is a wide yellowish to orange-yellow dorsal stripe, but with the side stripes absent or obscured.
There may be small alternating dark spots on the sides.
The throat is white or yellow, sometimes bright yellow.
The underside is bluish or greenish sometimes with pink or yellow marks.
Key to Identifying California Gartersnake Species

Life History and Behavior

Activity
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.
Defense
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.
Diet and Feeding
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. Leeches may also be consumed - I saw a recently-captured T. a. zaxanthus regurgitate two leeches.

Preston and Johnston, 2012, in their study of the diet of T. atratus in the Bay Area, found that native amphibians are a very important part of their diet, with Sierran Treefrogs being the most important amphibian prey, followed by California Toads, California Newts, and California Red-legged Frogs.

Adults have been found to forage actively, neonates are sit-and-wait foragers, and juveniles practice both forms of foraging.
Breeding
Courtship has been observed during March and April.
Young are born live late summer to early fall.

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.

Geographical Range
This subspecies, Thamnophis atratus atratus - Santa Cruz Gartersnake, is endemic to California.  According to Boundy, 1999 in his revision of T. atratus into three subspecies, Thamnophis atratus atratus occurs in the "Santa Cruz Mountains and the southern San Francisco Peninsula, from the San Andreas rift lakes to the San Lorenzo River watershed and Uvas Canyon." Intergrades with T. a. zaxanthus occur in the southern Santa Cruz Mountains.
(Authorities who do not recognize T. a. zaxanthus show the range of this subspecies also occurring in the East Bay south along the coast and inner south coast ranges into Santa Barbara County.)

The species Thamnophis atratus - Aquatic Gartersnake, ranges from Santa Barbara County north through the coast ranges into southwest Oregon.

Full Species Range Map
Notes on Taxonomy
This snake is known to hybridize with T. hammondii in Santa Barbara and San Luis Obispo Counties. 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 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. atratus
found in the east Bay and south along the inner coast ranges are now classified as T. a. zaxanthus by some taxonomists, including the taxonomy we follow here.


Alternate and Previous Names (Synonyms)

Thamnophis couchi atratus - Santa Cruz Garter Snake (Stebbins 1966, 1985, 2003)
Thamnophis couchi aquaticus - Aquatic Garter Snake (Stebbins 1966, 1985)
Thamnophis elegans aquaticus (Stebbins 1954)
Thamnophis elegans atratus (Stebbins 1954)
Thamnophis elegans aquaticus (Fox 1951)
Thamnophis elegans atratus (Kennicott 1860)
Black garter snake (Yarrow 1882)

Northern California coast garter
Middle California garter snake
Pacific coast garter snake
Single-striped garter snake
Western garter snake

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

atratus Santa Cruz Gartersnake (Kennicott, 1860)
Original Description
Thamnophis atratus - (Kennicott, 1860) - in Cooper, Expl. Surv. R.R. Miss. Pacific, Vol. 12, Book 2, Pt. 3, No. 4, p. 296

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

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

Other California Gartersnakes
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. 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

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.

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.

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

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.

1 Daniel L. Preston and Pieter T. J. Johnson. Importance of Native Amphibians in the Diet and Distribution of the Aquatic Gartersnake (Thamnophis atratus) in the San Francisco Bay Area of California. Journal of Herpetology 46(2):221-227. 2012

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
NatureServe Global Ranking
NatureServe State Ranking
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

 

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