Checkered Garter Snake
Thamnophis marcianus • Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: T. marcianus
Found in the Southwestern United States (Texas, New Mexico, Arizona, Oklahoma, California), Northern Mexico, and South into Central America (Belize, Guatemala, Costa Rica).
Look up Checkered Garter Snake in the Snake Encyclopedia →Venomous Status
Harmless / Non-venomous (though like many garters, they possess a modified Duvernoy's gland which produces a mild, non-medically significant saliva).
Danger Level
Harmless/Low Risk. They are not dangerous to humans or pets. Defensive bites may occur if handled, but they do not cause significant injury.
Family
Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: T. marcianus
Conservation
IUCN Red List: Least Concern. They are common throughout their range, though habitat loss and water pollution are localized threats.
Physical Description
Characterized by a distinct checkerboard pattern of black squares on a greenish-tan to yellowish background. A pale yellow or cream stripe runs down the center of the back. The head is relatively narrow with large eyes and round pupils. Scales are keeled.
Size & Dimensions
Typically ranges from 18 to 24 inches (45–61 cm), with a maximum recorded length of about 42 inches (107 cm). The specimen in the image appears to be a mid-sized adult.
Habitat
Primarily found in arid or semi-arid regions but always near a water source such as rivers, streams, ponds, or irrigation ditches. Often found in agricultural areas and suburban gardens.
Behavior & Temperament
Diurnal and crepuscular, active during the day or twilight. They are generally shy and will flee toward water or cover. If cornered, they may flatten their heads, strike, or release a foul-smelling musk and cloacal contents.
Diet & Feeding
Preys on amphibians (frogs, toads, tadpoles), fish, earthworms, and occasionally small lizards or rodents. They are active hunters that use their sense of smell to track prey.
Reproduction
Viviparous (gives birth to live young). Mating occurs in spring. Females give birth to litters of 6 to 30 young in the late summer or early fall.
Venom Profile
Non-venomous - no medically significant venom. Saliva may cause mild localized swelling in rare cases.
Look-alikes
Often confused with other garter snakes like the Western Ribbon Snake (Thamnophis proximus) or the Black-necked Garter Snake (Thamnophis cyrtopsis), but the distinct checkerboard spotting between the stripes is diagnostic.
Conservation Status
IUCN Red List: Least Concern. They are common throughout their range, though habitat loss and water pollution are localized threats.
Cultural Significance
As common garden inhabitants, they provide significant ecological services through pest control, specifically managing populations of slugs, snails, and various insects.
Notable Features
One of the few garter snake species specifically adapted to more arid environments, provided they have access to localized water. Their 'checkerboard' markings are more distinct than most other members of their genus.