(Thamnophis sirtalis)
The common garter snake is separated into 3 subspecies in the Pacific Northwest: The Puget Sound garter snake that lives on Vancouver Island, the valley garter snake that lives in the lower mainland, and the red-sided garter snake that lives in the interior and eastern points of the Province.
Adults can reach up to 2 m in length. While markings vary between the subspecies, all the garter snakes in the Pacific Northwest have a dark grayish-green body. They have a large pointed head and a yellow to greenish-yellow stripe down the back. The patterns and colour combinations on these snakes can be very beautiful to look at. Except for the mechanistic snakes, which can be all black.
If caught and held in your hand, a common garter snake will release a mix of musk and droppings from its vent. Quite often, they will twist and turn in your hands to ensure it is rubbed all over both the snake and you. If this strategy proves unsuccessful, they are known to flatten their heads and strike aggressively. On a walk in the forest one day, I had a very large snake attack my boot, and it would rear up. flatten his head and strike the toe of my boot. He did this over and over, I was fascinated by his aggressiveness; it was almost scary.
Common garter snakes spend the winter hibernating in communal dens. They may have to travel a few kilometres to reach a good den site, and these dens often are shared with many other garter snakes; sometimes, there can be thousands of them in one den. One den that l saw in Chilliwack must have had tens of thousands in it.
In the spring, males emerge from the den first, followed a short time later by the females. No sooner have the females emerged than the males begin to court them.
Often, many males will pursue a single female, the result is a mating ball of snakes, made up of many eager males, and somewhere in the middle of the ball, one single female. The first time I saw this, I was around 5 years old, and it scared the dickens out of me, but now it is an incredible sight to see.
Males are attracted to females by their smell and initiate mating by contact along the length of the female’s body. Once a female has mated, she seals off the opening to her reproductive tract with a plug. This prevents other males from mating with her. Males can sense this and usually do not pursue females who have already mated.
Common garter snakes are live-bearing. The young are born sometime in July or August. Females can have up to 75 young or as few as 5, but usually have around 15 young per litter. Biologists value the common garter snake in Canada as these snakes represent some of the northernmost populations of reptiles in the world. Our northern snakes reproduce less frequently and have larger young than their southern counterparts.
After mating, most common garter snakes migrate to summer hunting grounds. These areas are usually near water, where the snakes can forage, bask on cattail mats and logs, or dive underwater to avoid predators.
These snakes can orient using the position of the sun. This helps them find their way back to their dens in the fall.
They hunt primarily during the day but occasionally are seen foraging at night. They are cold-blooded and need warmth to be active. Adult snakes feed on slugs, frogs, toads, salamanders, tadpoles, and insects. Occasionally, they also eat small mammals, birds, fish, and other reptiles. Young snakes seem to exist mainly on earthworms.
Common garter snakes have a fascinating ability to deal with prey that other predators find toxic. These snakes can eat both the toxic rough-skinned newt and the poisonous western toad without any bad side effects.
Some common garter snakes will be melanistic. This pretty much means that the snake will be almost completely black. It is caused by an undue development of dark pigment in the skin. The word ‘melanism’ is derived from a Greek word that means black pigment. This affliction is quite common among not just these snakes but is often all across the animal kingdom. I find them quite fascinating to observe in the wild.