Description: With a maximum known length of 44 inches, it ranges in background color from olive to olive-brown to olive-gray with three stripes that run the length of the body. The middle dorsal stripe is yellow and darkens toward the tail. The pale yellow to light-tan lateral stripes distinguish the Mexican gartersnake from other sympatric (co-occurring) gartersnake species because a portion of the lateral stripe is found on the fourth scale row, while it is confined to lower scale rows for other species.

Habitat: This snake is strongly associated with permanent water with vegetation, including stock tanks, ponds, lakes, cienegas, cienega streams, and riparian woods. In the northern part of the range, the species is usually found in or near water in highland canyons with pine-oak forest and pinyon-juniper woodland, and it also enters mesquite grassland and desert areas, especially along valleys and stream courses.

Range: This species is known from central and southeastern Arizona (now rare) and extreme southwestern New Mexico in the United States, south through the highlands of western and southern Mexico to Oaxaca, at elevations of 53 to 2,590 m asl .

Found in these States: AZ | NM

Diet: The Mexican garter snake is classified as a terrestrial-aquatic generalist because it feeds on both aquatic and terrestrial prey. It has a varied diet consisting mainly of frogs, tadpoles, and fish, supplemented by lizards and mice. Native prey species play a large role in the ecology of Mexican garter snakes, and in areas where such prey is scarce, there are few garter snakes. Native prey such as the Chiricahua leopard frog and Gila topminnow are becoming increasingly rare.

Reproduction: Snakes breed in fall and early spring, and females store the sperm until ovulation in late March or early April. Like all garter snakes, the Mexican garter snake gives birth to live young instead of laying eggs. On average, about half the females in a population will give birth each year, and they will birth from 10 to 20 young. Young are born between early June and early July.

Status: Listed as Least Concern in view of its wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

Population trends clearly demonstrate that the Mexican garter snake is declining in the United States — many populations show negative trends, low densities, and the possibility of extirpation. There may be only a few hundred snakes in the United States, and present trends for the Mexican garter snake in the country can be expected to continue. Although little is known about the snake in Mexico, population decline can be expected there as well, since similar threats are present.

Subspecies: 10, with just one found in the United States:
   El Carmen Garter Snake - (Thamnophis eques carmenensis)
   Cuitzeo Garter Snake - (Thamnophis eques cuitzeoensis)
   Atotonilco-Cajititlan Garter Snake - (Thamnophis eques diluvialis)
   Southern Mexican Garter Snake - (Thamnophis eques eques)
   Zacapu Garter Snake - (Thamnophis eques insperatus)
   Northern Mexican Garter Snake - (Thamnophis eques megalops)
   Lake Chapala Garter Snake - (Thamnophis eques obscurus)
   Patzcuaro Garter Snake - (Thamnophis eques patzcuaroensis)
   Magdalena Garter Snake - (Thamnophis eques scotti)
   Blue-striped Mexican Garter Snake - (Thamnophis eques virgatenuis)

Taxonomy: