Common Garter Snake {Thamnophis sir talis) 



Description: The Common Garter Snake consists of two color phases in western Montana, both 

 ranging from 18-52" in length. Both phases have three yellow longitudinal stripes: one 

 located dorsally and one on each side. Between the yellow stripes is a black stripe broken 

 with red spots in one color phase but lacking red in the other. Ventral coloration varies from 

 yellow to bluish, and some individuals of the red-sided color phase have small black spots on 

 the edge of the ventral scales. The dorsal scales are keeled, and normally there are 7 upper 

 labial scales. 

 Young: The coloration of young snakes is similar to that of the adults; young are live-bom. 



Similar species: The Western Terrestrial Garter Snake has black spots overlapping the dorsal 

 yellow stripe; the background color between stripes tends to be brownish. The Plains Garter 

 Snake has the lateral yellow stripes on the 3rd and 4th scale rows above the belly scales and 

 the dorsal stripe is nearly always orange or rust-colored. 



Habitat and Habits: Garter snakes are found in all forest habitats but are more common at lower 

 elevations around marsh-bog-pond situations, where they prey on young fish, frogs, toads, 

 mice and invertebrates. One was found on the study area in an ephemeral pond. Typical of 

 most garter snakes, they emit a noxious secretion when handled and can be aggressive when 

 disturbed. Garter snakes eat a variety of vertebrates and invertebrates, with the Common 

 Garter Snake concentrating more on amphibians than the Western Terrestrial Garter Snake. 

 The Common Garter Snake is a live-bearer giving birth to 12-18 yoimg during the summer in 

 Colorado (Hammerson 1982a). 



Status: A single Common Garter Snakes was found on the study area. Given the small nimiber 

 of records from throughout the area, all records should be documented until the distribution is 

 better understood; of particular interest would be documentation of denning sites. Only the 

 red-sided color phase was observed in the present survey, however the color phase lacking 

 red spots should be watched for. The relative abundance of this species in this area compared 

 to the Western Terrestrial Garter Snake is not yet clear; in northwestern Montana the 

 Common Garter Snake is currently much less abundant. 



Montana Natural Heritage Program Rank: G5 S4. 



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