Sierra Gartersnake
Thamnophis couchii
![[Sierra Gartersnake]](/images/129ds.jpg)
Description
Physical
A medium sized slender snake, adults rarely exceed 90cm (36 inches). Scales are keeled, single anal plate. Typically has 8 upper labials, the 6th and 7th are not grossly enlarged compared to the 5th. Sixth upper labial is typically longer than the seventh. Rear chin shields seem to typically be about the same length as front but more data is needed. Internasals are longer than wide and appear pointed at the front. Typically has 21 dorsal scale rows at mid-body but occasionally has 19 or 20. Pupils are round.
Color and Pattern
Dusky olive or slate base color with two rows of alternating dark blotches on each side. On dark individuals, the blotches may not be distinct. Dorsal stripe is indistinct or absent. When absent, there usually is a remainder of it near the head.
In our area, the belly often has extensive marbling and black pigment. Throat usually also has black pigment, as does the head and upper labials.
Young are patterned like adults. In some populations, specimens may darken considerably with age.
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.
Males tend to have a high vental scale count and high subcaudal scale count than females.
Distribution Range
General range map taken from CWHR, modified.
Museum records taken from following institutions: CAS Herps, MVZ Herps, LSUMZ Herps.
Can be found on the valley floor east of the Sacramento River below Lake Shasta, especially in the south portion of the county (IE near Anderson), it primarily though ranges north from the Sierras into the Cascades through Lassen Nation Park and forest north to the Pit River Drainage where it then heads west to about Deep Creek, where it coexists with the Aquatic Gartersnake. While this snake can be found on the north side of the Pit River drainage, it does not seem to venture too far north of the Pit River.
Typical Elevation
We do not yet have enough records from distinct localities to calculate typical elevation. We need 7 more distinct localities.
Additional Information
Notes
The CWHR range map data for this species has been modified. The original range included a contact zone with the Aquatic Gartersnake (Thamnophis atratus) from the Pit River drainage all the way down to Tehama County. This is incorrect. Below the valid contact zone in the Pit River drainage, the species does not even approach the Aquatic Gartersnake range until the extreme southern part of the county, where there still is not a contact zone.
The range map needs further modification. I am hoping to accomplish that soon using data from Lousiana State University, which has an extensive specimen collection for this species originating in Shasta County.
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.
![[Sierra Gartersnake]](/images/129sm.jpg)
©Michael A. Peters
Adult. Posed on rock in front of Burney Creek, where it was found. Shasta County, CA.
![[Sierra Gartersnake]](/images/132sm.jpg)
©Michael A. Peters
Notice the black pigment on the head that helps differentiate this species from the Oregon Gartersnake. Also notice that the sixth upper labial is distinctively longer than the seventh. Burney Creek, Shasta County, CA.
![[Sierra Gartersnake]](/images/133sm.jpg)
©Michael A. Peters
Notice the dark ventral pigment that helps distinguish this species from the Oregon Gartersnake. Burney Creek, Shasta County, CA.
Habitat Shots
Unless otherwise noted, these habitat shots are from within Shasta County where this species is known to occur.
![[Sierra Gartersnake habitat]](/images/134sm.jpg)
Similar Species
Terrestrial Gartersnake
Terrestrial Gartersnakes (Thamnophis elegans) have a much more distinct dorsal stripe, the 6th and 7th upper labial are grossly enlarged compared to the 5th, the rear and front chin shields are about same length, and the internasals are wider than they are long and are not pointed in the front.
Aquatic Gartersnake
Aquatic Gartersnakes (Thamnophis atratus) generally lacks black pigment on labials, throat, and venter. The 7th upper labial is usually longer than 6th.
Common Gartersnake
Common Gartersnakes (Thamnophis sirtalis) a much more distinct dorsal stripe, have red blotches on the side, and typically have 7 upper labials.
![[Sponsor ShastaHerps.org]](/images/SherpBanner2.png)
