Unlike southern Idaho, north Idaho is thankfully devoid of poisonous snakes. The snakes that do live in the forested region of the north are harmless to humans and the ones you’ll most likely encounter are garter snakes.
Two types of garter snakes live in Boundary County–the common garter snake and the western terrestrial garter snake. Both have three cream to yellow stripes running down their length, with one dorsal (back) stripe and one on each side. The stripes on the western terrestrial garter snake can appear wavy because dark, pencil eraser-sized spots scattered over its back overlap the edges of the stripes.
Another way to tell the two snakes apart is the color between the stripes–the common garter snake is very dark to black while the western terrestrial garter snake is olive to greenish gray. Additionally, some common garter snakes have red spots on the sides of their bodies.
Both survive on a wide variety of prey. They both prey on earthworms, slugs, leeches, frogs, fish and mice. The western terrestrial garter snake also preys on tadpoles, snails, lizards, insects and carrion (roadkill) while the common garter snake rounds out its diet with toads, salamanders, some birds and the occasional insect or spider. Young common garter snakes primarily eat earthworms until they’re large enough to attack more challenging prey.
The garter snake’s habitat is as varied as its diet–anywhere associated with water, such as marshes, streams and ponds. They can also be found in open meadows and even swimming. Common garter snakes also venture into coniferous forests. The wide-range of habitats that garter snakes occupy, along with their varied diet makes it easy to understand why they are the most common snake in Idaho. Common garter snakes are also one of the most widely distributed reptiles in North America.
Since snakes are reptiles, they can either lay eggs or bear live young. Most snakes in Idaho are egg layers but both garter snakes bear live young, typically between July and September. The western terrestrial garter snake bears four to nine young while the common garter snake averages 13 to 26 young but has been known to have up to 85 young!
Birth isn’t the only time large quantities of snakes can be found together–snakes often group together during hibernation. Dozens to hundreds of garter snakes may congregate in hibernacula (winter dens) to spend the winter. Garter snakes often hibernate in crevices on south-facing rocky outcrops, which can include a natural rock wall in your yard.
During sweltering summer afternoons, garter snakes take shelter under logs, boards, rocks, leaf piles, firewood piles and anywhere else that is cool. They need the sun to warm their cold-blooded bodies, but they also need to seek shelter on hot days so they don’t overheat. Besides, when they are basking in the sun they are vulnerable to predators like skunks, raccoons, bears, hawks, owls, magpies and crows.
Even though garter snakes are not poisonous to people, they will emit a musky scent and/or fecal matter if they feel threatened by predators, including people.