Common Garter Snake

Valley garter snake (Thamnophis sirtalis fitchi), a subspecies of the common garter snake.

Gary Nafis, californiaherps.com CC BY-NC-ND 3.0.

General Description

Among the most fascinating and fear-inspiring creatures are snakes. With up to 13 recognized subspecies, the common garter snake (Thamnophis sirtalis) is one of the most widespread snakes in North America and is a snake you might have run into (or run from) before.

Common garter snakes can grow to a length of 86 cm (34 in), though they are commonly shorter. Females are larger than males and have longer tails. They are typically black, brown, gray, or green, and many have irregular red spots. Three brightly colored (usually yellow but sometimes white, green, or brown) stripes—matching the color of their underside—run along the length of their bodies, though sometimes the stripes are missing or are not well defined. Regional coloration varies, and in southern Oregon and northern California, a common subspecies, the valley garter snake (Thamnophis sirtalis fitchi), has a bright yellow dorsal stripe and bright red spots along the body.

Garter snake heads are wider than their necks, and their tongues are red, tipped in black. The scales of the common garter snake are keeled, meaning they have a raised ridge along their length.

Habitat and Distribution

Common garter snakes inhabit most of North America. While common garter snakes are highly adaptable and capable of surviving in extreme environmental conditions, they prefer to live in moist grassy environments and are often found near permanent surface water, like ponds, lakes, and streams, in part because they can flee into water when threatened. They use dens under rocks and other structures. As long as they have a suitable place to hide from predators, they can live in both urban and suburban areas.

Behavior and Feeding

They are active during the day, using their sense of smell and good vision to hunt. Common garter snakes consume a variety of prey, including earthworms, amphibians, leeches, slugs, snails, insects, crayfish, small fish, and other snakes. To help them control prey while eating them whole, common garter snakes produce toxic saliva.

The predators of common garter snakes include large fish, bullfrogs, snapping turtles, large birds, raccoons, and other snakes. The common garter snakes’ stripes serve as disruptive coloration that makes seeing them difficult for predators.

Common garter snakes typically brumate (the reptile version of hibernation in mammals) from late October through early April in natural cavities or burrows. While common garter snakes are usually solitary, they congregate in large numbers, including with snakes of different species, during the winter.

Evolution

One unique trait of the common garter snake is that it coevolved with the rough-skinned newt (Taricha granulosa), each animal driving the other to adapt. Rough-skinned newts have glands in their skin that produce a powerful neurotoxin that is lethal to most predators. Common garter snakes have evolved resistance to the toxin. In turn, rough-skinned newt populations that are preyed on by garter snakes respond by producing more potent toxin. In this way the two species have become locked into what is referred to as an evolutionary arms race.

Common garter snake head.

Gary Nafis, californiaherps.com CC BY-NC-ND 3.0.

Fun Facts

• Garter snakes give birth to live young rather than laying eggs. Females give birth to between 15 and 40 babies per mating season!

• A snake’s excellent sense of smell begins with its flicking tongue, which picks up scent chemicals of nearby predators and prey and transfers the chemicals to be “smelled” by the Jacobson’s (vomeronasal) organ in the top of its mouth, associated with the nasal cavity.

• Like many snakes, common garter snakes grow indeterminately, meaning they keep growing for their entire lifespan. Wild common garter snakes have an average life expectancy of about 4–10 years but can live up to 20 years in captivity.

Where to See

Common garter snakes have been documented in Crater Lake National Park, Redwood National and State Parks, Lassen Volcanic National Park, and Lava Beds National Monument, but are likely present in all Klamath Network parks.

Learn More

Common garter snake
https://www.nps.gov/bica/learn/nature/common-garter-snake.htm

Common garter snake - Oregon Department of Fish and Wildlife
https://myodfw.com/wildlife-viewing/species/common-garter-snake

Download a pdf of this article.

Prepared by Jeri Stoller, Scientists in Parks intern
NPS Klamath Inventory & Monitoring Network
Southern Oregon University
1250 Siskiyou Blvd
Ashland, OR 97520

Featured Creature Edition: January 2024

Thumbnail image credit: Gary Nafis, californiaherps.com CC BY-NC-ND 3.0.