American bullfrog

American bullfrog on a leaf field image, Rana catesbeiana
Common Name: American bullfrog
Scientific Name: Rana catesbeiana
Order: Anura
Family: Ranidae
Image Number: ROM2004_1062_6

Bullfrogs are common in eastern North America and are found in larger bodies of permanent water. The bullfrog is our largest frog species, growing up to 50 cm in body length. The background colour is usually a medium green, with a pattern varying from a few small dark spots to extensive dark mottling. The underside is usually white with occasional mottling. The throat is often tinged with yellow and may be bright yellow in males. The eardrum is larger than the eye in males, while it is about the same diameter as the eye in females. Tadpoles grow up to 10 cm in length, have a white opaque belly and are covered with small black dots.

Although adults seldom travel far from permanent water, young frogs often travel overland in search of new habitat. During this dispersal phase they may fall prey to snakes, birds, mammals or even larger frogs. Once the juveniles establish themselves in their new habitat, they are aquatic, seldom venturing far from water. Adults overwinter in underwater habitats. American bullfrogs feed on insects and other aquatic invertebrates, and even on other frogs.

American bullfrogs usually breed in June, later than most other amphibian species. The breeding period is extended over several weeks. Males set up territories in suitable breeding areas and advertise by emitting a distinctive two- or three-note bass call. Females are attracted by the calls and choose a mate on the basis of his territory. Up to 8000 eggs can be produced by a female, and after fertilization the eggs form a mat which floats at the water surface. The eggs hatch after a few days, and the larvae spend one or two winters as tadpoles before transforming.