bullfrog, common name of the largest North American frog, Rana catesbeiana. Native to the E United States, this species has been successfully introduced in the West and in other parts of the world. The body length is 4 to 8 in. (10–20 cm), and the legs may be up to 10 in. (25 cm) long. An aquatic form with fully webbed toes, the bullfrog can close its nostrils and lie at the bottom of a pond for some time. Males have a loud, booming call. Bullfrog tadpoles require two or three years to become adults. The bullfrog is the only frog whose legs are marketed in quantity for food in the United States. Several other large frogs of the genus Rana are called bullfrogs in other regions. Bullfrogs are classified in the phylum Chordata, subphylum Vertebrata, class Amphibia, order Anura, family Ranidae.