Common garter snake

Thamnophis sirtalis

We are lucky here in the Pacific Northwest to have a wide variety of variations of garter snakes to see when out in the wild. Often called “gardener” snakes, garter snake is the common name for the nearly harmless, small to medium-sized snakes belonging to the genus Thamnophis found over most of North America. Common garter snakes come in a wide range of colors, with a pattern of yellow stripes on a black, brown or green background, and their average total length (including tail) is about 22 inches.

Common garter snakes go into brumation (hibernation for snakes) in the winter time, and wake up as temperatures rise. When it starts to be consistently warm, people notice more snake activity, particularly piles of snakes out in warm areas on rocks, in the road, on trails and anywhere they can bask in the sun. These piles of snakes are trying to warm up, and mate. Male garter snakes wake up before females so that they can raise their body temperatures to optimum temperature to be on their game, before they start to put out the male hormone to tell the females it’s time. Males can also produce the pheromone that the females produce, in order to trick other males into starting a mating ball, before there is a female around to join. The ball warms up the male who was making false pheromones so that he can then lead the males away and circle back and start a new mating ball with the females.

After copulation, a female leaves the mating area to find food and a place to give birth. Female garter snakes are able to store the male’s sperm for years before fertilization. Their babies are incubated in the lower abdomen, at about the midpoint of the length of the female’s body. Garter snakes are ovoviviparous, meaning they give birth to live young. However, this is different from being truly viviparous, which is seen in mammals. Gestation is two to three months in most species. As few as three or as many as 80 snakes are born in a single litter!

Garter snakes have always been thought to be venom-less, but in reality, they have a venom that may be toxic to amphibians and other small animals. When researched, garter snakes were shown to have a mild venom in their saliva that is not dangerous for humans, though it may cause slight itching, burning, and/or swelling. Garter snakes also produce a nasty smell from their postanal glands when handled or threatened.

Often found in gardens in the summer, garter snakes can generally be found anywhere they can bask in the sun nearby some water. They don’t really have a home base, as they are solitary and take off soon after being born. They travel around looking for food and warmth until it’s time to group up in a communal den to bromate.

-Samantha Zeiner, Friends of Ridgefield NWR Staff