Reptiles
Mexican Garter Snake
Thamnophis eques · also called Mexican garter snakes
Along the edge of a slow desert stream, a Mexican garter snake hunts for tadpoles in water that, decades earlier, would have supported a far larger population of this same species before introduced fish and bullfrogs began quietly working against it.
Overview
The Mexican garter snake, Thamnophis eques, is an aquatic-leaning constrictor native to wetland habitat associated with rivers, ponds, and streams across the southwestern United States and much of Mexico. Its close dependence on aquatic prey, sharp decline driven by invasive predatory fish and bullfrogs, and federal threatened listing in the United States make it one of the more conservation-relevant garter snakes in North America.
A native squeezed out by newcomers
Rather than facing habitat loss alone, the Mexican garter snake has been pushed toward decline largely by species that were never supposed to be in its water at all, introduced predators and competitors it never evolved defences against.
Status
Vulnerable and federally listed as threatened in the United States, with significant declines in Arizona and New Mexico driven by invasive predatory fish and bullfrogs, though more stable in parts of central Mexico.
Mexican Garter Snake: common questions
Why has the Mexican garter snake declined so much in Arizona?
Introduced predatory fish and American bullfrogs, neither of which are native to the region, have significantly affected this species by directly preying on it and by competing for the same native aquatic prey it depends on, a combination of pressures that has driven substantial population declines in Arizona and New Mexico and led to the species' federal threatened listing.
Is the Mexican garter snake dangerous to people?
No, this species is entirely non-venomous to humans and poses no real danger, relying on its aquatic habitat and modest size to avoid predators rather than any capacity to seriously harm a person, even if handled or cornered.
How is the Mexican garter snake different from other garter snakes?
This species is more consistently tied to aquatic habitat throughout its life than several other garter snake species, which often range more widely into drier upland areas, reflecting the Mexican garter snake's heavier reliance on fish, frogs, and tadpoles found specifically along the edges of ponds, streams, and wetlands.
Where is the Mexican garter snake still doing well?
While populations in Arizona and New Mexico have declined sharply due to habitat loss and invasive predators, the species remains more stable across parts of central Mexico, where the same combination of introduced predatory fish and bullfrog pressures has not been as severe or widespread.