Red-sided Gartersnake

Thamnophis sirtalis

Species at Risk: Sensitive


The Red-Sided Garter Snake is a sub-species of the Common Garter Snake (T. sirtalis). There is some variation in color, but the most common coloration is dark green to black with 3 yellow stripes. Between the yellow stripes are vertical red to orange bars, which give this subspecies its name. They range in size from about 50 cm to 1.5 m, and are a very slender snake.

Red-sided garter snakes are famous for congregating in large numbers (hundreds to thousands) in their over-wintering sites, and then emerging in great numbers in the spring for a massive mating frenzy before dispersing. They are mature at 2-3 years of age. Mating balls of dozens of males will congregate around a small number of females. The famous Narcisse Snake Dens north of Winnipeg are occupied by red-sided garter snakes, as is the Lake Eden den site near Edmonton (see the projects page). Garter snakes are one of the species of snakes that bear live young (viviparous, as opposed oviparous, where they lay eggs). Each female can produce 10-30 offspring in the summer. They do also sometimes breed in the fall.

Contrary to popular belief, garter snakes are actually venomous, just not enough to be harmful to humans. Garter snakes feed on vertebrates, like frogs, toads, salamanders, fish, small mammals, birds and eggs, as well as invertebrates, like earthworms, leeches, and insects.

Given the dietary preferences of red-sided gartersnakes, they tend to live near bodies of water where they can find their prey, including ponds, creeks, marshes, ditches, streams, etc.

Red-sided garter snakes are currently considered secure in Alberta, though some local populations are under threat. Road mortality is a significant concern, especially in the spring when they are dispersing over many kilometers from their communal hibernacula. Given how many snakes will gather in a single den, they are also prone to natural disasters and human activity affecting their communal den sites, such as flooding, freezing, or attacks by misguided humans.

Peterson Field Guides: Western Reptiles and Amphibians (3rd ed) by Robert C Stebbins.
The amphibians and reptiles of Alberta : a field guide and primer of boreal herpetology (2nd ed) by Anthony P. Russell, Aaron M. Bauer, Wayne Lynch, and Irene McKinnon.
External link opens in new tab or windowCanadian Herpetological Society

Photo by Ian Kanda