Eastern Garter Snake

Overview:

Scientific Name: Thamnophis sirtalis sirtalis
Size: 18 – 54” (adult total length)
Status: Generally common to abundant.

 

Habitat:

Occupy a wide range of habitats, but are most abundant in moist grassy areas, especially near ponds, lake, ditch, or stream edges. Also found in vacant urban and suburban areas with artificial cover objects.

Adult Coloration:

Three light stripes on a usually black, brown, gray or olive background, though this species exhibits considerable color variation (see photos). Stripes may be yellow, greenish, brown, bluish, or white. One stripe extends down each side on scale rows 2 and 3 and one along the midline of the back. Often checkerboard pattern between the stripes. Sometimes stripes are absent; rarely, an individual will be uniformly dark (melanistic). Labial scales (along the mouth) yellow, usually with black edge, and tongue is red with a black tip. Chin, throat, and belly yellow, greenish, pale blue, or tan to white. Occasionally one or two small black spots on the edges of ventral (belly) scales.

Adult Characteristics:

Moderately large snake with keeled scales and a single (undivided) anal plate. Males smaller and more slender than females with longer tails.

Juvenile Characteristics:

Newborns with coloration similar to adults, and range from 5 – 9” in length.

Scale Count:

19 scale rows at midbody

Species Confused With:

Ribbon Snakes have side stripes on scale rows 3 and 4. Butler’s Garter Snake has a small head that is about the same width as the neck, and side stripe on the neck extends onto scale row 4. Melanistic (solid black) Garter Snakes have both heavily keeled scales and a single anal plate, unlike other solid black snakes in Michigan.

References:

• Amphibians and Reptiles of the Great Lakes Region by Jim Harding
• Harding, J.H. and J.A. Holman. 2006. Michigan Snakes. MSU Extension Ext. Bulletin E-2000,74 pp. [revised].
• Ruthven, A. G., H. B. T. Gaige, et al. 1912. The herpetology of Michigan, by Alexander B. Ruthven. Crystal Thompson and Helen Thompson; Memoranda towards a bibliography of the archaeology of Michigan, by Harlan I. Smith; prepared under the direction of Alexander G. Ruthven. Lansing, Mich., Wynkoop Hallenbeck Crawford, State Printers.
• Holman, J. A. 2012. The Amphibians and Reptiles of Michigan: A Quaternary and Recent Faunal Adventure. Detroit, Mich., Wayne State University Press.
• Conant, R., and Collins, J. T. 1998. Reptiles and Amphibians: Eastern, Central North America. Houghton Mifflin Harcourt Press.