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Red-sided Gartersnake

Red-sided gartersnake © Squamatologist CC BY-NC-ND 2.0

The gartersnakes, and other harmless snakes that bear live young, were formerly included in the family Colubridae but recently have been placed in the family Natricidae.


The red-sided gartersnake (Thamnophis sirtalis parietalis) is variable in colour but normally is dark green to black with three yellow stripes: one down the back and one on each side, on the second and third scale row. Between the yellow stripes down the back and sides are vertical red or orange bars. This species can grow to over one metre in length.

Red-sided gartersnake © Andrew DuBois CC BY-NC-SA 2.0

Similar Species

The red-sided gartersnake is very similar to the eastern gartersnake (of which it is a subspecies), Butler’s gartersnake and northern ribbonsnake. In Ontario, the red-sided gartersnake occurs only in the northwest, and neither the ribbonsnake nor Butler’s gartersnake occur that far north. Although many eastern gartersnakes exhibit strong reddish colouration, their red patterning often occurs on the chin and along the body below the lateral (side) stripes, whereas the red-sided gartersnake has red bars or spots between the dorsal (back) and lateral stripes.

Red-sided gartersnake © Andy Kraemer CC BY-NC-SA 2.0


The red-sided gartersnake is a habitat generalist and, during its active season, occupies habitat similar to that of the eastern gartersnake – forests, shrublands, wetlands, fields and rocky areas. High-quality hibernation sites that are deep and below the frost line are crucial for this snake, because its range reaches further north than that of any other land-dwelling reptile in Canada.

View an interactive map of the known ranges of red-sided gartersnakes in Ontario.

Have you seen a red-sided gartersnake?

Beaver River, Uxbridge © Sean Marshall


Red-sided gartersnakes generally breed in the spring, soon after emerging from hibernation, but also breed in the fall. In some areas, mating frenzies – involving many individuals, among which many males compete for access to a few females – occur near hibernation sites. Females typically give birth to 10 to 30 live young in midsummer but have been recorded as having up to 100 young! The young are 19 to 23 centimetres long at birth and mature in two or three years.

Following breeding, red-sided gartersnakes travel up to 20 kilometres from their hibernation sites to foraging grounds but return to the same den site in the fall. These snakes overwinter in deep crevices formed in rock and in sinkholes in grassy pastures. Because suitable sites are rare, hundreds and sometimes thousands of snakes may be found in one hibernaculum.

The red-sided gartersnake primarily eats frogs and leeches.

Other names: Coluber parietalis

Threats and Trends

This subspecies of the eastern gartersnake is abundant in its northern Ontario range and is able to persist in many human-modified landscapes. The greatest human-induced threat to this species is road mortality, especially during the period of emergence and dispersal when snakes travel great distances and cross roads. Because these snakes hibernate in large groups, occasional events, such as flooding of the den and freezing due to limited snow cover, can result in mass mortality. Although infrequent, these events are responsible for much more mortality than all other threats (e.g., road kill, predation) combined.

Current Status and Protection

Neither the Committee on the Status of Species at Risk in Ontario nor the Committee on the Status of Endangered Wildlife in Canada has assessed the status of the red-sided gartersnake. The species has no protection under the Ontario Fish and Wildlife Conservation Act and is not listed by the International Union for Conservation of Nature.

Learn more about reptile and amphibian conservation and what you can do to help these species on our Reptile and Reptile and Amphibian Stewardship page.