Three species of snake are known to Mayne Island, and all of them are garter snakes.
All three species are similar in appearance yet with practice may be distinguished from each other based on a few subtle features, including details in the way they look and how they behave. None of them are to be feared, for they are harmless and reclusive creatures.
Puget Sound garter snake (common garter snake)
The common garter snake (Thamnophis sirtalis) is perhaps the most distinctive of the three local species. It has a broad stripe down the back and two strongly contrasting side stripes along the length of its body. Ours is a particular subspecies known as the Puget Sound garter (T. s. pickeringii), which has a range limited to the coastal edges of the Salish Sea and across Vancouver Island. This snake varies in colour, which makes it easily confused with other species—especially the northwestern garter snake (Thamnophis ordinoides.)
Northwestern garter snake
Across its range, the northwestern garter snake is highly variable. It has the same striped pattern typical of other garters, but with spots that range in colouration across the rainbow. It can be pretty similar to the Puget Sound (common) garter. Locally, however, our northwestern garter tends to exhibit a more subtle complexion of earth-tones than the other species.
One way of telling this snake apart from the Puget Sound garter is to focus on its eyes. The eyes of the Puget Sound garter are much larger and bulge out from the head when viewed from above. The head of the northwestern garter is also relatively smaller.
Wandering garter snake
The third species of snake known to Mayne Island is the wandering garter snake (Thamnophis elegans vagrans), a subspecies of western terrestrial garter found in the southern Gulf Islands and in other regions throughout North America.
Several physical traits help set this snake apart from the others, including a dull, relatively uneven back stripe that fades into a dark-greyish ground colouration. However, it is the behaviour of this species that provides one of the best cues for recognition. The wandering snake has a habit of hunting for fish along shorelines—a behaviour unique to this species in our region. Both inland and coastal populations of western terrestrials have an affinity for water and are commonly regarded as “water snakes” for this reason. So if you happen upon a garter in the intertidal, you can be sure it’s the wandering one. Puget Sound and northwestern garter snakes have strictly land-based diets and won’t be found hunting along the coast.
All three local species of garter snake have been documented through inventory work conducted by the Mayne Island Conservancy. Yet there is also a notable historical report of the northwestern garter snake based on a specimen collected in 1966 by one of Canada’s most famous field naturalists, Ian McTaggart-Cowan.
How To Get Help Identifying Garter Snakes
This article provided a few tips on identifying our local garter snakes, though it should be noted that accurate IDs sometimes rely on more precise features, such as the number of labial scales or size of inter-nasal scales. Yet while the identification of these snakes can at times be challenging, those who know them well can often reliably identify them from a photograph. Try sharing a photograph on the Mayne Island Biodiversity project, if ever you find yourself scratching your head. Who knows, you might turn up another species, such as the rare sharp-tailed snake. This snake has been found on several surrounding gulf islands but has yet to be documented on Mayne Island.