Checkered Garter Snake
Thamnophis marcianus • Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: T. marcianus
Southwestern United States (Texas, Oklahoma, New Mexico, Arizona, California) and south through much of Mexico into Central America (Belize, Guatemala, Honduras, Nicaragua, Costa Rica).
Look up Checkered Garter Snake in the Snake Encyclopedia →Venomous Status
Non-venomous (though like all garter snakes, they possess a Duvernoy's gland that produces mild saliva not dangerous to humans).
Danger Level
Harmless; they generally prefer to flee. If handled, they may bite or release a foul-smelling musk and cloacal contents.
Family
Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: T. marcianus
Conservation
IUCN Red List: Least Concern. Generally abundant, though local populations can be threatened by habitat loss or water pollution.
Physical Description
Characterized by a greenish, tan, or straw-colored background with a prominent checkered pattern of dark square spots. It typically has three light stripes: one down the center of the back and one on each side. The head is relatively narrow with large eyes and round pupils.
Size & Dimensions
The specimen in the image appears to be a juvenile or small adult, approximately 30-50 cm. Adults typically range from 45 to 105 cm (18-42 inches).
Habitat
Semi-aquatic specialists found in arid and semi-arid regions near permanent or intermittent water sources like streams, ponds, irrigation ditches, and damp woodlands from sea level to about 2,200 meters.
Behavior & Temperament
Primarily diurnal but may become crepuscular or nocturnal in extreme heat. They are active foragers with a nervous temperament, quickly fleeing toward water or cover when threatened.
Diet & Feeding
Generalist carnivores that consume amphibians (frogs, toads, tadpoles), fish, earthworms, and occasionally small lizards or rodents using active foraging and quick strikes.
Reproduction
Viviparous (gives birth to live young) rather than laying eggs. Litter sizes vary greatly, typically between 6 to 30 young, usually born in mid-to-late summer.
Venom Profile
Non-venomous - no medically significant venom.
Look-alikes
Other garter snake species (Thamnophis sirtalis or T. cyrtopsis) can look similar; however, the specific placement of the lateral stripes on the 2nd and 3rd scale rows and the distinct checkered pattern are diagnostic for T. marcianus.
Conservation Status
IUCN Red List: Least Concern. Generally abundant, though local populations can be threatened by habitat loss or water pollution.
Cultural Significance
Often valued by gardeners and farmers as a form of natural pest control for slugs and insects; frequently kept as pets due to their manageable size and hardiness.
Notable Features
Excellent swimmers that often dive underwater to escape predators; they are highly adaptable to human-altered landscapes like suburban gardens and agricultural drainage systems.