The Common Garter Snake: Stripes, Live Young and an Arms Race With a Newt

One of North America's most widespread snakes

Snakes are among the most fascinating — and most feared — of creatures. With up to 13 recognized subspecies, the common garter snake (Thamnophis sirtalis) is one of the most widespread snakes in North America, and one you may have met, or run from.

What it looks like

• Size: up to 86 cm (34 in) long, though usually shorter. Females are bigger than males, with longer tails.
• Color: typically black, brown, gray or green, often with irregular red spots. Three stripes — usually yellow, sometimes white, green or brown, matching the belly — run the length of the body, though they can be faint or missing. Color varies by region: in southern Oregon and northern California, a common subspecies, the valley garter snake (Thamnophis sirtalis fitchi), has a bright yellow stripe down its back and bright red spots along its body.
• Head and scales: the head is wider than the neck, the tongue is red with a black tip, and the scales are keeled — each has a raised ridge along its length.

Where it lives

Common garter snakes live across most of North America. They're highly adaptable and can survive extreme conditions, but prefer moist, grassy places, often near permanent water — ponds, lakes and streams — partly because they can escape into it when threatened. They use dens under rocks and other structures, and can live in cities and suburbs too, as long as they have somewhere to hide from predators.

Hunting, and being hunted

• Prey: active by day, they hunt by smell and good vision, eating earthworms, amphibians, leeches, slugs, snails, insects, crayfish, small fish and other snakes. Toxic saliva helps them control prey they swallow whole.
• Predators: large fish, bullfrogs, snapping turtles, large birds, raccoons and other snakes. The stripes work as disruptive coloration, making the snake hard for predators to see.
• Winter: from late October to early April, they brumate — the reptile version of hibernation — in natural cavities or burrows. Usually solitary, they gather in large numbers in winter, even with other kinds of snake.

An evolutionary arms race

The common garter snake has coevolved with the rough-skinned newt (Taricha granulosa), each driving the other to adapt. Glands in the newt's skin make a powerful neurotoxin that kills most predators — but the garter snake has evolved resistance to it. Newt populations hunted by garter snakes respond with stronger toxin, locking the two species in an evolutionary arms race.

Fun facts

• Garter snakes bear live young instead of laying eggs — 15 to 40 per mating season.
• Their flicking tongue picks up scent chemicals from predators and prey and delivers them to the Jacobson's (vomeronasal) organ in the top of the mouth, which is linked to the nasal cavity.
• Like many snakes, they grow indeterminately — they keep growing all their lives. In the wild they live about 4–10 years on average, and up to 20 years in captivity.

Where to see one

Common garter snakes have been recorded at Crater Lake National Park, Redwood National and State Parks, Lassen Volcanic National Park and Lava Beds National Monument, and are likely present in all the parks of the Park Service's Klamath Network.

More: the Park Service's common garter snake page and the Oregon Department of Fish and Wildlife.

Sources

Based on Jeri Stoller (Scientists in Parks intern, Klamath Inventory and Monitoring Network), "Common Garter Snake," Featured Creature, January 2024, National Park Service; published by the National Park Service and in the public domain; rewritten in hubnx's own words. Its photographs, licensed CC BY-NC-ND, and the network's logo are not reproduced.