Squamata suborder Serpentes
Thamnophis sirtalis -- Common Gartersnake
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Purple shade indicates vouchered specimens. Light blue (cyan)
shade indicates photographic records. Yellow shade indicates verified
sighting. Slanted hatch indicates pre-1980 records only
NOTE: Not all specimens upon which these maps are based have been verified.
Key Characters: Side stripes on scale rows 2-3; yellow or gray midback stripe; black bars on margins of labial scales; back scales strongly keeled; anal scale not divided.
Similar Species: Eastern ribbonsnake, western ribbonsnake, plains gartersnake, lined snake.
Subspecies: Chicago garter snake, T. s. semifasciatus; eastern garter snake, T. s. sirtalis.
Description: Medium-sized (up to 100 cm TL) dark brown or black snake with a yellow or gray midback stripe and a yellow stripe on each side. Belly gray-green with dark spots on edges of most belly scales. Head usually without parietal light spots. Some individuals have red coloring between side scales. In T. s. semifasciatus, the side stripe near the head is broken into a dashed line by black crossbars.
Habitat: Forests and edge habitats, commonly near water. Vacant lots in cities.
Natural History: Cold-tolerant snake that occasionally emerges from hibernation to bask on warm winter days. Mates immediately after emerging from hibernation, as early as March in southern counties. Females give birth to 15-80 young from July through early October that are 15-20 cm TL. Diet includes fish, amphibians, young birds, and a variety of invertebrates. Eaten by a wide variety of predatory vertebrates; people needlessly kill many.
Status: Common throughout the state.