Non-native Frog Survey Natural History of the American bullfrog Rana catesbeiana in British Columbia Bullfrogs are the largest frog in North America. Bullfrogs prefer warm, weedy, permanent ponds and lakes. However, they are sometimes found in small ditches and along slow moving streams. Bullfrogs emerge from winter torpor in April.
Adults bask on the surface of the water or on the shore but always remain close to the water.
They are very wary during the day and may disappear quickly if approached closely. Adult bullfrogs are known to be voracious predators and their diet includes insects, young birds, mice, fish, snakes and, most importantly, other frogs including smaller bullfrogs. Young bullfrogs mainly eat insects. Herons, otters, mink, ospreys and kingfishers will all prey upon small bullfrogs but larger individuals are beyond the grasp of most of the predators in our region. In late spring, male bullfrogs establish breeding territories which they aggressively defend from other males.