T. couchii is highly
aquatic and diurnal. It spends much of its time in the water or basking on rocks and vegetation at the water's edge. They are capable of crawling on stream bottoms and hunt actively underwater, relying heavily on their eyesight. When threatened, the Sierra garter snake will often attempt to flee into the water. If captured or cornered, it defends itself by striking repeatedly and releasing a foul-smelling musk and cloacal contents. During winter months, especially at higher elevations in the Sierra Nevada, the snakes undergo
brumation (hibernation) in communal dens for several months.
Diet The diet of the Sierra garter snake consists almost entirely of aquatic prey, primarily fish and
amphibians, including frogs, tadpoles, and aquatic salamander larvae. They are notable for their ability to safely consume highly toxic
Pacific newts (genus
Taricha), such as the California newt (
Taricha torosa), having evolved a genetic resistance to their deadly tetrodotoxin. There is a distinct ontogenetic shift in their feeding habits: adult snakes tend to forage in deeper, faster-moving water for larger prey like Pacific giant salamander larvae, while neonates and juveniles hunt smaller prey along the shallow stream margins. ==Reproduction==