Common Garter Snake
Thamnophis sirtalis • Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: Thamnophis sirtalis
Widely distributed across North America, ranging from the subarctic regions of Canada to the southern tip of Florida, and from the Atlantic coast to the Pacific coast.
Look up Common Garter Snake in the Snake Encyclopedia →Venomous Status
Mildly venomous (opisthoglyphous/rear-fanged), but functionally harmless to humans.
Danger Level
Harmless/Low Risk. Bites may cause minor localized itching or swelling in sensitive individuals, but they do not pose a health threat to humans or pets.
Family
Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: Thamnophis sirtalis
Conservation
Least Concern (IUCN). Extremely stable population, though some local subspecies like the San Francisco Garter Snake are endangered due to habitat loss.
Physical Description
Features three light stripes (yellow, green, or blue) running longitudinally down a dark body. The background color is typically black, brown, or olive. The scales are keeled (ridged), the head is slightly wider than the neck, and the pupils are round.
Size & Dimensions
The specimen in the image appears to be a sub-adult or small adult, approximately 18-24 inches. Adult species range from 18 to 26 inches on average, with a maximum record of about 49 inches.
Habitat
Extremely versatile; found in meadows, marshes, woodlands, and suburban gardens. Primarily stays near water sources but can inhabit fields and forests far from water. Elevation ranges from sea level to high mountain meadows.
Behavior & Temperament
Diurnal and active. When threatened, they may flatten their heads, strike (often with a closed mouth), or release a foul-smelling musk from their cloaca. They are generally shy and prefer to flee.
Diet & Feeding
Generalist carnivore feeding on earthworms, amphibians (frogs, toads, salamanders), fish, and occasionally small rodents or birds. They use active foraging to find prey and swallow it alive.
Reproduction
Viviparous (gives birth to live young). Breeding occurs in spring shortly after emerging from brumation. Litters are large, typically ranging from 10 to 40 neonates, born in late summer.
Venom Profile
The venom is neurotoxic but very mild and produced in the Duvernoy's gland; it is effective on small prey like amphibians but lacks clinical significance for humans.
Look-alikes
Ribbon Snakes (Thamnophis saurita) which are more slender with stripes on different scale rows; Lined Snakes (Tropidoclonion lineatum) which have a double row of black spots on the belly.
Conservation Status
Least Concern (IUCN). Extremely stable population, though some local subspecies like the San Francisco Garter Snake are endangered due to habitat loss.
Cultural Significance
One of the most commonly encountered snakes in North America, often serving as an 'ambassador species' for reptile education. They play a vital ecological role in controlling pest populations.
Notable Features
High tolerance for cold temperatures, often being the first snake to emerge in spring. They are also known for forming 'mating balls' where dozens of males swarm a single female upon emergence from hibernation.