Common Garter Snake
Thamnophis sirtalis • Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: T. sirtalis
Widely distributed across North America, ranging from the subarctic regions of Canada to the Southern United States, and from the Atlantic to the Pacific coast.
Look up Common Garter Snake in the Snake Encyclopedia →Venomous Status
Mildly venomous (Rear-fanged/Opisthoglyphous); they possess a Duvernoy's gland but lack a high-pressure delivery system.
Danger Level
Harmless/Low Risk; bites to humans usually result in nothing more than minor localized swelling or itching. They are not considered medically significant to humans.
Family
Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: T. sirtalis
Conservation
Least Concern (IUCN); very common and adaptable, though threatened locally by habitat loss and pesticide use.
Physical Description
Features three light-colored longitudinal stripes (yellow, green, or blue) on a dark background. Between the stripes are rows of alternating black spots. The head is distinct from the neck, with large eyes and round pupils. Scales are keeled (ridged).
Size & Dimensions
The specimen appears to be an adult approximately 18-24 inches long. The species typically ranges from 18 to 26 inches, with a maximum recorded length near 49 inches.
Habitat
Extremely versatile; found in forests, fields, prairies, and suburban backyards. They have a strong preference for being near water sources such as ponds, marshes, and streams, from sea level to high elevations.
Behavior & Temperament
Active primarily during the day (diurnal). Generally timid and will flee if approached. If cornered, they may flatten their heads, strike, or release a foul-smelling musk from their cloaca.
Diet & Feeding
Generalist carnivores that feed on earthworms, slugs, frogs, toads, salamanders, fish, and occasionally small rodents. They are active foragers and do not constrict, instead swallowing prey alive.
Reproduction
Ovoviviparous (giving birth to live young). Mating occurs in spring shortly after emerging from brumation. Litters typically range from 10 to 40 young, though larger litters are possible.
Venom Profile
The venom is mildly neurotoxic and contains proteolytic enzymes, but it is primarily effective on small amphibians and fish.
Look-alikes
Ribbon Snakes (Thamnophis saurita) are slimmer with longer tails; DeKay's Brownsnakes (Storeria dekayi) lack the prominent side stripes and have different spotting.
Conservation Status
Least Concern (IUCN); very common and adaptable, though threatened locally by habitat loss and pesticide use.
Cultural Significance
Highly valued as a beneficial garden guest for controlling pest populations like slugs and insects. They are one of the most recognized and familiar snakes to the North American public.
Notable Features
They are one of the few snake species that are resistant to the toxins found in North American newts and toads, allowing them to exploit a food source that is lethal to other predators.