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Red-sided Gartersnake

Thamnophis sirtalis parietalis

Family: Colubridae

The Red-sided Gartersnake is a subspecies of the Common Gartersnake (Thamnophis sirtalis).

COSEWIC status:
  • Not Assessed
SARA status:
  • No Status
IUCN status:
  • Least Concern


The Red-sided Gartersnake is variable in colour but normally is dark green to black with three yellow stripes: one down the back (dorsal stripe) and one on each side (lateral stripes). The lateral stripes are on the second and third scale row. Between the yellow stripes down the back and sides are vertical red or orange bars interspersed within the dark background colour. The red pattern may be limited on some individuals, and vibrant on others. Individuals can grow to over one metre in length.

Similar Species

The Red-sided Gartersnakes may be confused with other Gartersnake species with which its range overlaps: the Terrestrial Gartersnake, Plains Gartersnake and Eastern Gartersnake. All three of these species lack the distinct red bars within the dark background between the lateral and dorsal stripes, though they may have red in their yellow lateral stripes. The Terrestrial Gartersnake usually has eight scales on its upper lip and rows of black spots that invade the dorsal stripe, causing the dorsal stripe to have a jagged or wavy edge. The lateral stripes on the Plains Gartersnake are on the third and fourth scale rows and the dorsal stripe is often a vibrant orange.


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In Canada, the Red-sided Gartersnake occurs from northwestern Ontario to eastern British Columbia. An isolated population exists in the southern part of the Northwest Territories and northern Alberta. This sub-species occurs throughout the central United States as far south as Texas. Including all subspecies, the Common Gartersnake is found throughout much of southern Canada and most of the United States, with the exception of the driest areas in the southwest, and in a small part of northern Mexico.


The Red-sided Gartersnake is a habitat generalist and, during its active season, occupies forests, shrublands, wetlands, fields and rocky areas. These snakes overwinter bellow the frost line in mammal burrows, rock crevices, talus slopes, anthropogenic structures (e.g. old foundations, cisterns) and other underground cavities. 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. Red-sided Gartersnakes are commonly found under cover objects, such as rocks and logs, which provide important microhabitat for shelter and thermoregulation.


Red-sided Gartersnakes generally breed in the spring, soon after emerging from hibernation, but also breed in the fall. In some areas, mating frenzies – among which many males compete for access to a few females – occur near hibernation sites. Females typically give birth to 10-30 live young in midsummer. The young are 19-23 cm long at birth and mature in two or three years. Following breeding, Red-sided Gartersnakes may travel many kilometres from their hibernation sites to foraging grounds but return to the same den site in the fall. Because suitable hibernation sites are rare, hundreds and sometimes thousands of snakes may be found in one hibernaculum. The Red-sided Gartersnake primarily forages during the day and eats a wide variety of prey, including frogs, toads, salamanders, earthworms, leeches, insects, small fish, small mammals and occasionally birds and eggs. This species can live for more than twenty years.


The greatest 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 events. Although intensive habitat loss is a threat to all snakes, this species is able to persist in areas with low to moderate human disturbance. Human persecution and subsidized predation may also present a risk to this species in areas of high human density. 

Additional Information About This Species In Canada