A Guide to the Amphibians
and Reptiles of California



Key to California Gartersnakes


These pages may also be useful when identifying California gartersnakes:

Range maps
of all CA gartersnakes

ID page
including pictures of all CA gartersnake species.


In most parts of California, several species of gartersnake inhabit the same area - including as many as four species in some areas. These snakes can often be identified on sight, but sometimes measuring or counting certain scales is necessary to identify a species, especially with snakes in areas where there are species that are similar in appearance, or with snakes that do not have the appearance typical of their species or subspecies.

Observing and comparing the scales and features listed in the chart below should help to identify the species of most gartersnakes encountered in California. For more detailed information about scale counts, see the books listed below under references.

Scale counts can vary within a particular species, so counting scales will not always work. (For example, T. ordinoides usually has 7 upper labials and 17 mid-body scale rows, but sometimes it has 8 upper labials and 19 mid-body scales, while the same counts are possible with T. elegans which typically has 8 upper labials and 21 mid-body scales.) Comparing all scales is not always helpful either. For example, comparing anal scales is not necessary as all species should have a single anal scale, and comparing the placement of the lateral stripe is not necessary since all California species typically have the lateral stripes on the 2nd and 3rd scale rows (except for Marcy's Checkered Gartersnake, which can be easily identified without looking at the lateral stripes.)
Click on a name link for more information about a snake.
Click on a blue link to see an illustration of the scale count.

Snake

Upper Labials Lower
Labials
Chin Shields Internasals Scale Count
at Mid-body
Some features differing from sympatric gartersnakes Snake
Thamnophis atratus atratus

Santa Cruz Gartersnake
8

6 and 7 not enlarged

11 Rear pair longer
than front

Longer than wide and pointed in front
19 or 21 8 upper labials. Chin shields. Internasals. Yellow on throat. May be missing lateral stripes. No red on sides or head.
gartersnake
Thamnophis atratus hydrophilus

Oregon Gartersnake
8

6 and 7 not enlarged
usually 10 Rear pair longer
than front

Longer than wide and pointed in front
19 or 21 8 upper labials. Chin shields. Internasals. Vertebral stripe often absent, or present only on neck. Underside of tail often orange or pinkish. No red on sides or head. gartersnake
Thamnophis atratus zaxanthus

Diablo Range Gartersnake

8

6 and 7 not enlarged
11 Rear pair longer
than front

Longer than wide and pointed in front
19 or 21 8 upper labials. Chin shields. Internasals. No red on sides or head. gartersnake
Thamnophis couchii

Sierra Gartersnake
8

6th is wider
than 7th

  Rear longer than front in this example Longer than wide,
pointed in front
19 or 21 Unstriped morph with no stripes.Upper labials. gartersnake
Thamnophis elegans elegans

Mountain Gartersnake
8

Occasionally 7
6 and 7
are enlarged, higher than wide

10 Front and rear pairs equal in length
Wider than long,
not pointed in front

21

Rarely 19
No red on sides. Dorsal and lateral stripes. Upper labials. Chin shields. Internasals. gartersnake
Thamnophis elegans terrestris

Coast Gartersnake
8

Occasionally 7
6 and 7
are enlarged, higher than wide

10 Front and rear pairs equal in length
Wider than long,
not pointed in front

21

Rarely 19
Red spotting on sides. Upper labials. Chin shields. Internasals. gartersnake
Thamnophis elegans vagrans

Wandering Gartersnake
8

Occasionally 7
6 and 7
are enlarged, higher than wide

10 Front and rear pairs equal in length
Wider than long,
not pointed in front

21

Rarely 19
Upper labials. Chin shields. Internasals. Greyish ground color with black checking and yellow lateral and vertebral stripes. gartersnake
Thamnophis gigas

Giant Gartersnake
8

6th is shorter than 7th

10 - 11   The internasals are slightly shorter than the prefrontals 23 or 21
Large body size. 6th Upper labials. gartersnake
Thamnophis hammondii

Two-striped Gartersnake
8
      21 Lack of vertebral stripe. No red on sides. gartersnake
Thamnophis marcianus

Marcy's Checkered Gartersnake
8
      21 or 19 Black area of head color
extends downward covering the 7th & 8th upper labials. Only gartersnake in its range in California.
gartersnake
Thamnophis ordinoides

Northwestern Gartersnake
7

Sometimes 8,
rarely 6

8 - 9

Rarely 7 or 10
Rear longer
than front
The internasals are shorter than the prefrontals 17

Rarely 15 or 19

Occasional lack of lateral stripe. Upper labials. Internasals. Highly variable in color and pattern and scalation. Small head.

gartersnake
Thamnophis sirtalis fitchi

Valley Gartersnake
7
Occasionally 8, rarely 6 or 9

Often with
black wedges

10
Rear longer
than front

Internasals 19 Dark with red spotting on sides. Yellowish vertebral and lateral stripes. Little or no red on head. Large eyes. Upper labials. Chin shields. gartersnake
Thamnophis sirtalis infernalis

California Red-sided Gartersnake
7
Occasionally 8, rarely 6 or 9

Often with
black wedges

10
Rear longer
than front

Internasals 19 Red on sides and head. Upper labials. Chin shields. gartersnake
Thamnophis sirtalis tetrataenia

San Francisco Gartersnake
7
Occasionally 8, rarely 6 or 9

Often with
black wedges

10
Rear longer
than front

Internasals 19 Usually a continuous red lateral stripe bordered with black.Lateral stripes and belly greenish blue. Upper labials. Chin shields. gartersnake

Snake

Upper Labials Lower
Labials
Chin Shields Internasals Scale Count
at Mid-body
Some features differing from sympatric gartersnakes Snake



Compare T. atratus, T. elegans, T. sirtalis, T. couchii

Compare T. sirtalis (left) with T. ordinoides (right) by the tops of their heads


References

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.

St. John, Alan D. Reptiles of the Northwest: Alaska to California; Rockies to the Coast. Lone Pine Publishing, 2002.

Brown, Philip R. A Field Guide to Snakes of California. Gulf Publishing Co., 1997.

Behler, John L., & F. Wayne King. The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, 1992.

Brown et. al. Reptiles of Washington and Oregon. Seattle Audubon Society, 1995.


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