Garter snakes are one of North America’s most widespread snake groups, commonly encountered across diverse landscapes. These slender reptiles are generally considered harmless to humans. Their remarkable adaptability has allowed them to thrive in a wide array of environments.
North American Distribution
Garter snakes, belonging to the genus Thamnophis, exhibit an expansive geographic range. They are found throughout Canada, extending into every province and even reaching the southernmost Northwest Territories. Their distribution continues across the United States, stretching from Florida on the eastern seaboard to British Columbia in the west, and reaching as far south as the Gulf of Mexico. Isolated populations also exist in mountainous regions of New Mexico and northern Mexico.
The common garter snake (Thamnophis sirtalis) is particularly notable for its widespread occurrence. This broad distribution highlights the group’s capacity to adapt to varied climatic conditions and ecological zones. While the group as a whole is widely distributed, individual subspecies, such as the Maritime garter snake or the red-sided garter snake, may have more localized ranges within this extensive territory.
Preferred Living Environments
Garter snakes inhabit a diverse range of environments. They frequently occur in moist, grassy areas and are often found near permanent water sources, including ponds, lakes, ditches, streams, and marshes. Their semi-aquatic nature means they are equally comfortable on land and in water, often fleeing into water when threatened.
Beyond aquatic margins, these snakes also occupy grasslands, meadows, and forest edges. They adapt to human-modified landscapes, residing in suburban gardens, parks, and agricultural areas. Within these habitats, garter snakes seek shelter in microhabitats such as under rocks, logs, leaf litter, and dense vegetation. These sheltered spots provide protection from predators and the elements, enabling them to thrive in varied settings where essential resources are available.
Factors Shaping Their Presence
The presence of garter snakes is influenced by the availability of food, water, and suitable cover, alongside appropriate climate conditions. Their diet is varied, consisting of amphibians like frogs and salamanders, earthworms, slugs, and small fish. They are opportunistic carnivores, also consuming small birds and rodents. The abundance of these prey items dictates where garter snakes establish populations.
Access to water is a factor, as many species are semi-aquatic and rely on aquatic prey. Additionally, garter snakes are ectothermic, relying on external heat sources for body temperature regulation. They require a thermal gradient within their environment, utilizing basking spots to warm up and cooler areas for refuge. This influences their activity patterns and habitat selection, leading them to seek cover under rocks, logs, or other debris to bask or escape extreme temperatures. They brumate (a form of reptilian hibernation) during colder months, often congregating in communal dens.