Common Garter Snake
Thamnophis sirtalis
![[Common Garter Snake]](/images/130ds.jpg)
Description
Physical
A medium sized slender snake, adults rarely exceed 120cm (48 inches). Scales are keeled, single anal plate. Typically has 7 upper labials, apparently about 1 in every 5 has 8 upper labials on one or both sides. Rear chin shields are longer than front. Eyes noticeably larger in relation to head than our other species. Pupils are round.
Color and Pattern
In our area, these snakes typically have a dark base color with a yellow or cream dorsal stripe and two cream side stripes where the dorsal scale rows meet the belly scales (one stripe on each side.)
The most distinctive feature in our area that allows us to readily identify this species on sight are the red blotches along the side just above the side stripes.
Young are patterned like adults.
Sexual Dimorphism
Males tend to have longer tails that are noticeably fat after the vent, females have slightly shorter tails that taper off quickly after the vent. Some people are quite accurate at determining sex by tail geometry, but probing is required for most of us to be certain.
Habitat
Often found near permanent sources of water that have True Frog (Family Ranidae) populations or trout, these snakes are adept swimmers and are frequently found in the water.
Diet
An opportunistic feeder, they largely feed upon aquatic prey, including frogs, fish, salamanders, and amphibian larvae. This species is one of the few species that is able to withstand the toxins of Pacific Newts.
Young usually feed upon earthworms and Central Pacific Chorus Frogs.
Distribution Range
General range map taken from CWHR.
Museum records taken from following institutions: CAS Herps, CAS-SUR, MVZ Herps, LSUMZ Herps.
Found throughout Shasta County. Ironically, despite the common name, they seem to be less likely to be found in the lower Sacramento River valley than the Terrestrial Garter Snake, though they are in the valley.
Typical Elevation
Based on records in our database, in Shasta County the Common Garter Snake is typically found at elevations from 211m to 1955m (693ft to 6412ft). Minimum elevation we have a record for is 196m (643ft). Maximum elevation we have a record for is 2022m (6632ft).
Reproduction and Young
Mating usually occurs in the spring though fall matings have been observed. Females give live birth, clutch size usually less than 2 dozen though significantly larger clutch sizes have been observed.
Taxonomy
The subspecies that occurs in our area is the Valley Garter Snake (Thamnophis sirtalis fitchi).
Pronunciation
The assumed IPA pronunciation of this species: /θɑm ˈnɑ fis/ /sɜr ˈtɑ lis/
Taxonomic Etymology
Thamnophis is a concatenation of two Greek words. θάμνος means shrub or bush. όφις means snake. It is a reference to the tendency of these snakes to be found in the vicinity of bushes.
sirtalis is apparently a reference to a garter, probably in reference to the dorsal stripe (Beltz 2006). I have not yet found the linguistic origin.
fitchi honors Henry Sheldon Fitch (Beltz 2006).
Taxonomy Notes
Additional Information
Images
Unless otherwise noted, all images are of wild specimens in Shasta County.
Please be kind, do not hotlink images and do not use images without permission of the copyright owner.
![[Common Garter Snake]](/images/59sm.jpg)
![[Common Garter Snake]](/images/130sm.jpg)
![[Common Garter Snake]](/images/127sm.jpg)
©Watermark Testing
Upper Labial Count. The Common Garter Snake is the only Shasta County Garter Snake that typically has 7 upper labials. McCloud River. Shasta County, CA.
![[Common Garter Snake]](/images/128sm.jpg)
©Watermark Testing
Front and Rear Chin Shield comparison. In Common Garter Snake, the rear chin shields are noticeably longer than the front chin shields. McCloud River. Shasta County, CA.
Habitat Shots
Unless otherwise noted, these habitat shots are from within Shasta County where this species is known to occur.
![[Common Garter Snake habitat]](/images/131sm.jpg)
Similar Species
Terrestrial Garter Snake
In Terrestrial Garter Snakes (Thamnophis elegans), the rear chin shields are about the same length as the front chin shields. They also typicaly have 8 upper labials and in our area lack red blotches on the side.
Aquatic Garter Snake
Aquatic Garter Snakes (Thamnophis atratus) in our area usually have a weak or missing dorsal stripe, typicaly have 8 upper labials and lack red blotches on the side.
Sierra Garter Snake
Sierra Garter Snakes (Thamnophis couchii) usually have a weak or missing dorsal stripe, typicaly have 8 upper labials, and lack red blotches on the side.
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