[8] Thamnophis elegans occurs in a wide variety of habitats, including grasslands, woodlands, and coniferous forests, from sea level up to 3,962 m (12,999 ft).

[10]The diet of Thamnophis elegans depends heavily on the prey available in the local area, and thus varies due to regional geographical differences.

This makes the western terrestrial garter snake an excellent example of polyphagism—the adaptation of an organism to maintain a varied diet.

Meanwhile, more inland or montane populations are often found adjacent to fresh water sources such as creeks, rivers, streams, ponds, or lakes.

Coastal snakes are less likely to respond to chemical cues received from fish, which can be inferred by less rapid tongue-flicking when around them.

[11] When hunting, the Western Garter Snake's actions are chemically and visually mediated on land and in water.

[12] These differences in diet and foraging behavior between coastal and inland snake populations suggest that the species has undergone microevolution.

Due to dietary and foraging differences between variants of T. elegans, it can be inferred that coastal populations have filled a niche in the environment that allows them to no longer rely on fish as a major food source.