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A Guide to the Amphibians
and Reptiles of California


Diablo Range Gartersnake - Thamnophis atratus zaxanthus

Boundy, 1999
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Diablo Range Gartersnake Diablo Range Gartersnake Diablo Range Gartersnake Diablo Range Gartersnake
  Adult 1, Contra Costa County  
Diablo Range Gartersnake Diablo Range Gartersnake Diablo Range Gartersnake Diablo Range Gartersnake
Adult 1, Contra Costa County Adult 2, Contra Costa County
Diablo Range Gartersnake Diablo Range Gartersnake Diablo Range Gartersnake Diablo Range Gartersnake
Adult, Contra Costa County Adult in shallow water,
Contra Costa County
Adult, Contra Costa County Sub adult, Contra Costa County
Diablo Range Gartersnake Diablo Range Gartersnake Diablo Range Gartersnake Diablo Range Gartersnake
Juvenile, Contra Costa County Neonate, late August,
Contra Costa County
Adult, Contra Costa County

Adult, Alameda County
© Adam Clause
       
Feeding
Diablo Range Gartersnake Diablo Range Gartersnake Northern Pacific Rattlesnake Northern Pacific Rattlesnake
Adult eating a Bullfrog tadpole in Santa Clara County. © Chad Lane

Janet heard squeaking then saw a gartersnake rolling and twisting down an incline. When they stopped, the snake was the victor in a struggle with a vole. Solano County. © Janet Ellis
Diablo Range Gartersnake Diablo Range Gartersnake    
Adult eating a frog (possibly a Foothill Yellow-legged Frog) at the edge of a creek in Santa Clara County © Douglas Brown    
   
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.  
   
Habitat
Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat
Habitat, Contra Costa County
Habitat, spring, Contra Costa County
Habitat, spring, Contra Costa County Habitat, Alameda County
Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat
Habitat, Contra Costa County
Habitat, small pond, Contra Costa County
Habitat, summer, Contra Costa County
Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat Variegated Skink Habitat  
Habitat, Alameda County

Habitat, Alameda County Habitat, 500 ft, western
Stanislaus County
 
       
Short Videos
Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat Diablo Range Gartersnake Habitat  
Diablo Range Gartersnakes in and around a small cattle pond in Contra Costa County. Diablo Range Gartersnakes swimming in another cattle pond in Contra Costa County. When it is picked up, a big adult Diablo Range Gartersnake demonstrates how it smears foul-smelling fluids from its cloaca all over the hand of its tormentor. Too bad they haven't invented online video with smells yet....  
     
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
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.

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. 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..."
Color and Pattern
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.
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) but small fish are also eaten, and possibly small rodents. Leeches are also 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 zaxanthus - Diablo Range Gartersnake, is endemic to California.  According to Boundy, 1999 in his original description of this snake, Thamnophis atratus 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.

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
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 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.)

T. a. zaxanthus
is still classified as T. a. atratus by some researchers.


Alternate and Previous Names (Synonyms)

Thamnophis atratus zaxanthus - Diablo Range Garter Snake (Stebbins & McGinnis 2012)
Thamnophis atratus zaxanthus - Diablo Range Garter Snake Boundy, 1999
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

zaxanthus Diablo Range Gartersnake Boundy, 1999
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

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

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

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.

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

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, 1957.

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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