Northern Mexican Garter Snake

DESCRIPTION:
The Northern Mexican garter snake is a subspecies of the Mexican garter snake (Thamnophis eques). This subspecies is a medium to large-bodied with adults reaching upwards of about 0.5 to ~1 m. The scales are keeled and the dorsum is generally olive, olive‑brown, or olive‑gray with three yellow (or pale) stripes that run along the body (a dorsal stripe and two lateral stripes). A series of dark, square, or crescent shaped blotches may be present between the stripes, particularly in juveniles. It is important to note the distinguishable trait, from other co-occurring garter snakes, is the confinement of the lateral lines on scale rows three and four. The middle dorsal stripe is yellow and darkens towards the tail. The head is relatively broad and distinct from the neck with light‐colored crescents behind the corners of the mouth.

DISTRIBUTION & STATUS:
Historically distributed across central and southeastern Arizona, southwestern New Mexico, and throughout much of western and central Mexico. In Arizona, the subspecies occupied riparian corridors within the Gila, Salt, San Pedro, Santa Cruz, and Verde river systems. Current populations are highly fragmented and reduced due to widespread habitat degradation and the introduction of non-native predators. Currently, the status of the Northern Mexican garter snake is federally threatened. Arizona and Mexico has designated critical habitat for this species and is protected by law under the Endangered Species Act.

HABITAT:
Occupies a range of low- to mid-elevation riparian habitats characterized by a perennial water source. Preferred habitats include aquatic grasses, stock ponds, and backwaters with dense vegetation The species requires adequate structural cover and basking areas, and is closely tied to aquatic habitats that support viable amphibian and fish populations. Habitat use is both aquatic and semi-terrestrial, with individuals moving into adjacent uplands for thermoregulation and overwintering.

FOOD HABITS:
An opportunistic predator with a generalized diet. They primary prey includes amphibians (frogs and tadpoles) and fish. When aquatic prey are scarce, they also eat terrestrial prey such as lizards and small rodents.

REPRODUCTION:
The Northern garter snakes are viviparous and give birth to live young, rather than laying eggs. Mating occurs in late spring following emergence from hibernation. The late spring to early summer is when they will mate and parturition typically occurs from June to early August. Litter size often ~10‑20 young, but can vary (some reports of up to ~25 in optimal cases). It is important to note that a successful litter depends on habitat, condition of individual, and food availability. Therefore, some individuals may not reproduce that year. Sexual maturity is generally reached around 2 years for males and 2-3 years for females. Females may exhibit biennial reproduction in resource-limited environments.