Checkered Garter Snake
Thamnophis marcianus • Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: Thamnophis marcianus
Found in the Southwestern United States (Texas, Oklahoma, New Mexico, Arizona, California) and south through much of Mexico and Central America into Costa Rica.
Look up Checkered Garter Snake in the Snake Encyclopedia →Venomous Status
Non-venomous (though like many colubrids, possesses a Duvernoy's gland that produces mildly toxic saliva which is harmless to humans).
Danger Level
Harmless. These snakes pose no threat to humans or pets; they are not aggressive and prefer to flee when encountered.
Family
Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Natricinae, Genus: Thamnophis, Species: Thamnophis marcianus
Conservation
IUCN Red List: Least Concern. The species is widespread and adaptable, though localized populations may be threatened by loss of wetland habitats.
Physical Description
Characterized by a distinct checkered pattern of dark square spots on a tan, olive, or yellowish-green background. A pale cream or yellow stripe runs down the center of the back, and similar stripes appear on the lower sides (on the 3rd and 4th scale rows). The eyes have round pupils, and the scales are heavily keeled.
Size & Dimensions
The specimen in the image appears to be a sub-adult, roughly 40-50 cm in length. Adults typically range from 45 to 75 cm, with a maximum recorded length of about 108 cm.
Habitat
Semi-aquatic and versatile; typically found near water sources like streams, ponds, and irrigation ditches in arid or semi-arid regions. Also inhabits grasslands and desert scrub, ranging from sea level to approximately 2,200 meters.
Behavior & Temperament
Diurnal or crepuscular, especially active during cooler parts of the day in hot weather. They are generally docile but may release a foul-smelling musk from the cloaca and flatten their heads defensively if handled.
Diet & Feeding
Generalist carnivores that utilize active foraging. Their diet includes amphibians (frogs and toads), fish, earthworms, and occasionally small rodents or lizards.
Reproduction
Viviparous (gives birth to live young). Breeding occurs in spring, and females give birth to 6 to 30 young between June and August.
Venom Profile
Non-venomous - no medically significant venom. Saliva may cause mild localized swelling in very rare sensitive cases.
Look-alikes
Often confused with other garter snakes like the Western Terrestrial Garter Snake (T. elegans) or Ribbon Snakes (T. proximus). It is distinguished by the cream-colored crescent markings behind the corners of the mouth and the specific scale rows of the lateral stripes.
Conservation Status
IUCN Red List: Least Concern. The species is widespread and adaptable, though localized populations may be threatened by loss of wetland habitats.
Cultural Significance
Commonly encountered by gardeners and farmers, they provide significant ecological services by controlling populations of agricultural pests and garden slugs.
Notable Features
This species is noted for its high tolerance to the toxins found in the skins of certain toads, which are a primary food source for many populations.