Cottonmouths are opportunistic predators feeding mainly on fish, frogs, smaller snakes, turtles, small mammals, birds, crayfish and large insects. Hatchlings start on insects, frogs, lizards and small fish. Adults may consume prey up to 1/3 of their own body size.
Cottonmouths use venom to immobilize their prey before swallowing it whole. They locate prey using specialized infrared heat-sensing pits near their nostrils. These allow them to strike accurately even in dark water.
Cottonmouths often wait in ambush concealed near water’s edge or under vegetation. They may also actively pursue prey in shallows and along banks. Larger rodents, birds, snakes, and turtles are consumed by adult cottonmouths. Fish become a primary prey source for adults in regions where abundant.