Thamnophis sirtalis

The coloration varies geographically and is difficult to characterize succinctly. These snakes have 19 dorsal scale rows at mid-body, a pale lateral stripe on each side on the 2nd and 3rd scale rows (also on row 4 in subspecies annectans of Texas-Oklahoma), 7 scales on each upper lip, 1 preocular (scale in front of eye), 3 postoculars (scales behind eye), keeled scales on the back, and an undivided anal scale (covers vent). Adult total length is usually 16-26 inches (41-66 cm), with the maximum around 52 inches) (131 cm). Newborns are around 5-7 inches (12-23 cm) in total length (Conant and Collins 1991, Smith and Brodie 1982).

This species differs from other sympatric garter snakes by the following combination of characteristics: lateral stripe confined to 2nd and 3rd scale rows (except in annectans), seven scales along each upper lip; tail less than 27% of total length, and 19 scale rows at mid-body.

Throughout the range, common gartersnakes inhabit a very wide range of aquatic, wetland, and upland habitats; habitat preference exhibits rather pronounced regional differences (e.g., east vs. west). In some regions, such as much of eastern North America, these snakes are decidedly terrestrial and range far from water. In other areas, such as the Rocky Mountain region, they are mostly confined to riparian corridors. When inactive, they occur underground, in or under surface cover, or in other secluded sites.

In some areas, common gartersnakes spend the cold winter months completely submerged in water. Submerged snakes retain more body water and conserve more stored energy than do snakes in dry sites. At the low temperatures of hibernation, the snake's metabolic rate is very low, so oxygen needs can be met even while the snake is submerged and unable to breathe air.

Home range size variously reported as 0.8 ha to 14 ha (DeGraaf and Rudis 1983). In the far northern part of the range, thousands may aggregate at hibernacula. Population density estimates in different areas range from about 10/ha to 100/ha.

In much of the range, mating occurs primarily in spring, just after emergence from hibernation, though possibly to a limited extent also in late summer. Adult females give birth usually in July or August but earlier in the south and as late as early October in the north. Litter size averages about 13-26 but varies geographically (generally larger in the east than in the west); the largest females tend to produce the largest litters. Individuals become sexually mature in 1-2 years. In Northwest Territories, Canada, females evidently rarely gave birth in successive years (Larsen et al. 1993). See Cover and Boyer (1988) for information on captive breeding.