General Description: The Common Gartersnake is a slender, medium-sized snake. Adults range from 18–30 inches (45.7–76.2 cm) in total length. The coloration of Common Gartersnakes varies across their range, but in South Dakota, individuals have a tan or pale yellow middorsal stripe extending down the entire length of the body. The background coloration is typically tan and an additional lateral stripe exists on each side of the body that occurs on scale rows two and three. Patterning and coloration between the middorsal and lateral stripes can be variable, but it is generally a red and black checkerboard pattern. All individuals have keeled scales, an undivided anal scale, and white ventral (belly) scales. Similar to other gartersnakes, females reach larger lengths and weights than males and there are no external characters that can be used to differentiate males from females. Typically, males have a longer tail length relative to the total length, while females have a smaller tail length that quickly tapers to a point. Common Gartersnakes are similar in appearance to Plains Gartersnakes (Thamnophis radix) but can be identified by the lateral stripe occurring on scale rows two and three (instead of scale rows three and four in Plains Gartersnakes).
Behavior: Common Gartersnakes are typically active from March to November, but this can vary regionally. This is an active, primarily diurnal species of snake, though, during the summer may shift activity to become more nocturnal to avoid activity during the heat of the day. Typically beginning in October these snakes will begin to move to overwintering hibernacula. Hibernacula are often rock crevices, mammal burrows, artificial (man-made) cover such as under concrete or wood piles. On warm days from November to March, individuals can be found emerging from hibernacula to bask in the sun, though they will not move far from the entrance. Prey consists mostly of amphibians, fish, earthworms, or other soft-bodied invertebrates. Unlike most other colubrid snakes, Common Gartersnakes do not constrict prey, but instead, subdue and rapidly consume prey. When threatened, Common Gartersnakes will often flatten and extend their bodies, displaying the red coloration between and on the scales, and upon capture will release a foul-smelling musk.
Reproduction: Males of this species typically emerge in advance of females from hibernation around March and will wait near the hibernacula for females to emerge. Once a female emerges, multiple males will attempt to court her. Eventually, a male is successful in breeding with this female who then disperses away from the hibernacula. Males will continue to stay at the hibernacula attempting to mate with females for several weeks. Females give live birth to an average of 20 young in the late summer. Sexual maturity is reached typically in two years.
Habitat: Common Gartersnakes are typically found in close association with aquatic habitats. These include rivers, lakes, reservoirs, wetlands, and riparian corridors. Unlike Plains Gartersnakes, Common Gartersnakes are rarely found in dry habitats away from water sources.
Species Range: Common Gartersnakes are found across most of the United States and southern Canada, but are absent from much the Rocky Mountains and desert Southwest.
South Dakota Range: It is predicted that Common Gartersnakes can be found across South Dakota; however, many voucher specimens are lacking from the northern and central regions of the state.
South Dakota Status: This species is not listed by South Dakota Game, Fish and Parks.