|A relatively long, stout-bodied garter snake where females may reach a length of 112 cm. (44 in.). Mexican garter snakes have 3 bold stripes and are easily confused with the black-necked and checkered garter snakes that are found throughout their range. All 3 species can be identified by noting which scale rows the lateral stripe falls across in the anterior portion of the body. Mexican garter snake’s lateral stripe occurs on scale rows 3 & 4, on rows 2 & 3 on black-necked garter snakes and row 3 in checkered garter snakes.
An extremely aquatic, secretive garter snake, it is rarely found away from permanent water and dense vegetation. In Arizona, it inhabits cienegas, cienega-streams and cottonwood-willow riparian areas. Mexican garter snakes are distributed from southern Mexico north through the Mexican Plateau and Highlands to central Arizona and west-central New Mexico. Historically, in Arizona, they were found at low- to mid-elevations, 530-1875 m. (1720-6150 ft.), throughout the greater Gila River Basin and the headwaters of the Rio Yaqui (San Bernadino National Wildlife Refuge). Once common in the Tucson Basin, it is now extirpated from the area.
Mexican garter snakes primarily feed on frogs and fish although they are known to take small rodents and lizards. Females give birth to up to 25 live young between late May and early July. They are active during the warmer months of the year and are most readily observed in the morning. If handled or threatened, Mexican garter snakes will strike repeatedly and bite, all the while smearing a strong smelling musk and feces on the handler.
Mexican garter snakes have declined throughout much of their range in Arizona and are considered a Species of Special Concern by the Arizona Game and Fish Department and it is illegal to handle or collect them without the proper permits. Although Mexican Garter snakes do not have official Federal protection, much of their remaining habitats are protected, at least in part, due to the Federal listing, under the Endangered Species Act, of several other wetland obligate species including Sonoran Tiger salamanders, Chiricahua leopard frogs and Huachuca water umbel.
Reasons for decline include alteration and destruction of their aquatic habitat and the introductions of exotic species (e.g., bullfrogs). Surveys conducted during the mid-1980’s and 2000 suggest this trend is continuing. On a positive note, a population in Santa Cruz Co., which was thought to be extirpated, was recently found to persist there, albeit in low numbers.
In Arizona the subspecies Thamnophis eques megalops, Northen Mexican Garter snake is found.
by Eric Wallace
Originally published in the Sonoran Herpetologist "Herpetofauna of the 100-mile Circle" 15 (10) 2002