General Description: The Plains Gartersnake is a slender, medium-sized snake. Adults range from 16–28 inches (40.6–71.1 cm) in total length. The coloration of Plains Gartersnakes varies across their range, but in South Dakota, individuals have a wide bright yellow or orange middorsal stripe extending down the entire length of the body. The background coloration is typically tan to brown and a light yellow lateral stripe exists on each side of the body that occurs on scale rows three and four. Patterning and coloration between the middorsal and lateral stripes is variable, even within a region, though there are two common forms: 1) a series of alternating black spots (checkerboard in appearance) on a tan background, or 2) almost a solid black phase where spots are almost indistinguishable from the background coloration (see photos). 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. Plains Gartersnakes are similar in appearance to Common Gartersnakes (Thamnophis sirtalis) but can be identified by the lateral stripe occurring on scale rows three and four (instead of scale rows two and three in Common Gartersnakes).
Behavior: Plains 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. Frequently, these snakes are found in basements of homes or barns as temperatures begin to cool as individuals are searching out hibernacula. On warm days between November–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, however, they are also known to consume small mammals and chicks of ground nesting birds. Unlike most other colubrid snakes, Plains Gartersnakes do not constrict prey, but instead, subdue and rapidly consume prey.
Reproduction: Males track females via pheromone trails and during the breeding season (April–May) multiple males may attempt to court a single female. Females reach sexual maturity in their second or third year of age. Plains Gartersnakes give birth to live young from in later summer, typically July through September, after a gestation period of approximately three months (90 days). Clutch sizes range from 5–60 young but usually are from 10–20. The largest known clutch size of Plains Gartersnakes was from a female from Edmunds Co., South Dakota who produced 97 offspring (Smith & Zimmer 2013. Herpetol. Rev. 44:454).
Habitat: Plains Gartersnakes are found in most habitats across South Dakota, including prairies, wetlands, and riparian corridors. Additionally, they can be common in residential areas, including vacant lots. Plains Gartersnakes can be found in drier habitats and at greater distances from aquatic habitats than the Common Gartersnake.
Species Range: Plains Gartersnakes are found throughout the North American Great Plains region, from the Oklahoma and Texas panhandles north to southern Canada, and east through Minnesota, Wisconsin, and Indiana.
South Dakota Range: Plains Gartersnakes can be found across South Dakota and are one of the most common snakes in the state.
South Dakota Status: This species is not listed by South Dakota Game, Fish and Parks.