The garter snake, belonging to the genus Thamnophis, is one of the most recognized and widespread snakes across North America, ranging from central Canada to Central America. These snakes are generally harmless to humans and are not considered venomous, though they do possess a mild toxic saliva used for subduing small prey. Their adaptability allows them to thrive in various environments, making them a common sight in gardens, fields, and near water sources. Characterized by their slender bodies and distinctive longitudinal stripes, garter snakes are often the first snake species many people encounter in the wild.
Identifying Garter Snakes
Garter snakes are typically small to medium-sized, with adults commonly measuring between 18 and 36 inches in total length, though some individuals may reach up to 54 inches. Their body color is highly variable, ranging from black, brown, and olive to greenish-gray. They are defined by a pattern of three light-colored stripes that run the length of their body, contrasting against the darker background color. The stripes can be yellow, white, green, or even blue or red.
One stripe runs down the center of the back (dorsal stripe), and one lateral stripe is located on each side of the body, usually on the second and third rows of scales above the belly. Their scales are keeled, meaning each scale possesses a raised ridge that gives the snake a slightly rough or textured appearance. The head is only slightly wider than the neck, and they have large eyes with round pupils.
Differentiating the garter snake from its close relative, the ribbon snake (Thamnophis saurita), is important as they share a similar striped pattern. Ribbon snakes are noticeably more slender and have a proportionally longer tail, making up about one-third of their total body length, compared to the garter snake’s shorter tail. Additionally, ribbon snakes often have a distinct white or pale spot just in front of the eye, a feature absent in garter snakes. Common water snakes (Nerodia species) are generally thicker-bodied, lack continuous longitudinal stripes, and have a more aquatic lifestyle.
Geographic Range and Environment
The genus Thamnophis boasts one of the widest distributions of any snake in North America, extending from the subarctic plains of Canada down into the neotropics of Costa Rica. This extensive range is a testament to the snake’s high degree of adaptability, allowing it to survive in diverse climates and ecosystems. They are found across all of the lower 48 United States and nearly all Canadian provinces.
Garter snakes are often found in environments that provide a balance of cover and moisture, such as meadows, woodlands, prairies, and suburban gardens. They tend to prefer habitats near water sources, including the edges of ponds, streams, marshes, and ditches, largely because many of their prey items are aquatic or semi-aquatic. Although they are often near water, they are versatile enough to thrive in relatively drier environments.
Brumation
During the colder months, garter snakes participate in brumation, which is the reptile equivalent of hibernation. They often migrate to communal sites called hibernacula, which can be natural cavities, rodent burrows, or spaces under rocks or building foundations. These dens can sometimes host hundreds of snakes clustered together for warmth and protection. The ability to gather in large groups helps them endure prolonged periods of cold temperatures.
Feeding Habits and Prey
Garter snakes are opportunistic carnivores, and their diet is highly varied, shifting based on what prey is locally abundant and available to them. They are active foragers, hunting primarily during the day when temperatures are suitable for their metabolism. Their proficiency as hunters is supported by an excellent sense of smell, which they use by flicking their tongue to gather chemical cues from the environment.
Their primary prey includes soft-bodied animals such as earthworms, slugs, and leeches. They also consume a variety of amphibians, including frogs, toads, and salamanders, showing a notable tolerance for the toxins present in the skin secretions of some toads. Larger adult snakes may expand their diet to include small fish, insects, crayfish, and occasionally small rodents, lizards, or nestling birds.
The snake subdues its prey by swallowing it whole, often relying on its quick reflexes and mild toxic saliva. This saliva, produced by the Duvernoy’s gland, is a weak neurotoxin that aids in incapacitating small prey but is not considered medically significant or harmful to humans. The snake’s lack of specialized fangs means the saliva is not efficiently delivered, minimizing any risk to larger animals.