Plains Garter Snake {Thamnophis radix) 



Description: The Plains Garter Snake ranges from 16-42" in length and has a dorsal background 

 color of olive, brown, or black. It has a prominent orange or yellow dorsal stripe and a 

 greenish-yellow stripe on each side located on the 3rd and 4th scale rows above the belly 

 scales. It typically has black vertical bars on the upper lips. 

 Young. Young are live-bom and resemble adults. 



Similar species: The other garter snakes found in Montana have the lateral yellow lines on the 2nd 

 and 3rd scale rows above the belly scales. 



Habitat and Habits: Plains Garter Snakes are found in prairie habitats but are most common 

 around wetland areas, where they feed around permanent and semi-permanent water bodies. 

 In 1998, as many as 22 individuals, both adults (80-85 cm total length) and juveniles (30-40 

 cm total length) were seen along 400 m of shoreline at a single site (Blackfoot Reservoir, 

 Carter County); most were sunning in or near shallow water around the reservoir with little 

 emergent vegetation present. Fish, frogs, toads, mice and invertebrates are the most common 

 food items in the diet of the Plains Garter Snake (Hammerson 1982a, Baxter and Stone 1985). 

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

 aggressive when disturbed. The Plains Garter Snake is a live-bearer, giving birth to 9-21 

 young during mid- to late-summer in Colorado (Hammerson 1982a). In 1998, this species 

 was documented during surveys between 28 April and 24 July. 



Surveying: Timed sight surveys may be conducted around wetlands and riparian feeding areas or 

 at denning areas where higher concentrations of garter snakes occur, clear mornings may be 

 the best survey times. Much distribution information may come from recording incidental 

 sightings. More intensive research may be done using funnel traps in combination with drift 

 fences. More intensive research and survey projects may use mark-recapture or 

 radiotelemetry techniques. 



Status: This species is found over much of eastern Montana, particulariy in the far eastern and 

 north-central portions of the state. It is the most common garter snake in eastern Montana. 

 Former status is unclear due to conflision in the identification of the 3 garter snakes that occur 

 in the plains region. In 1998, this species was documented at 21 survey sites in 8 counties 

 (Appendix 2). There were 7 additional encounters in 6 counties (2 counties not included in 

 the survey records: Appendix 4). It should be watched for and any sightings should be 

 documented with a description written at the time of observation, including how radix was 

 distinguished from the other garter snakes. Of particular interest would be documentation of 

 any denning sites located. 



Montana Natural Heritage Program rank: G5 S4. 



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