Information Last Reviewed Spring 2007
Native to the eastern United States, bullfrogs have been introduced to much of the rest of the continental United States and Hawaii. In some introduced areas, absence of natural predators has resulted in high bullfrog population densities, overwhelming native fauna. Significant adverse impacts, primarily through predation, have been documented on populations of native amphibians, reptiles, and fish.
Broadly webbed hind feet
Long hind legs, with dark cross bars usually evident
Teeth in upper jaw
Tympanic membrane (eardrum) distinct; larger in males
No dorsolateral ridges
One of few North American frogs to exceed 4" snout-to-vent length
Principally nocturnal, but potentially active any time of day
Semi-aquatic as adults, aquatic as larvae (tadpoles)
Adults are predatory; tadpoles feed on algae and vegetation
Highly adept at jumping, especially when startled
Hibernate in muck during cold weather
Males vocalize to attract females during the breeding season
Bullfrogs are true frogs (order Anura), exhibiting smooth skin, long hind legs with extensively webbed hind feet, and teeth in the upper jaw. Their large size, distinct tympanic membranes (eardrums), absence of dorsolateral ridges, and breeding call distinguish this species from most other North American frogs. Adult bullfrogs are greenish, brownish, or sometimes blackish, and may exhibit dark spots or mottling dorsally. Ventral coloration ranges from whitish to yellowish, with or without dark mottling. Male bullfrogs exhibit a yellow throat, and the tympanic membrane is approximately twice the size of the eye (female tympanic membranes are roughly equal to the size of the eye). Tadpoles are greenish to yellowish with black spots dorsally and are usually whitish ventrally. Tadpoles may metamorphose during their first year or overwinter and metamorphose during their second year.
True frog appearance (smooth skin, long hind legs, fully webbed hind feet, teeth in upper jaw) distinguishes the bullfrog from all North American spadefoots, toads, treefrogs, and narrow-mouthed toads.
Large size (4" or greater snout-to-vent), absence of dorsolateral l ridges, and breeding call distinguish the bullfrog from most other North American true frogs.
May be mistaken for green frogs (Rana clamitans), pig frogs (Rana grylio), or river frogs (Rana hecksheri): The ranges of these three species overlap the native range of the bullfrog.
Bullfrog life cycles include an aquatic larval stage and a semi-aquatic adult stage. Bullfrog populations may reach high densities in areas devoid of natural predators (fish, snakes, turtles, etc.)
Aquatic, gilled tadpoles
Tadpole stage may persist for up to 2 years and reach 3" in length
After one or two years, tadpoles metamorphose into adults
Reproduction occurs in permanent water bodies between February and July
Males attract females by calling (a deep, hoarse "ba-rum" or "jug-o-rum")
Mating occurs in water; males clasp females and hold them in amphiplexus
Females release eggs while in amphiplexus; eggs are surrounded by a gelatinous sheet that adheres to vegetation
Fertilization is external
Gelatinous sheets may contain up to 20,000 eggs; females may produce multiple clutches during the breeding season
Wide variety of permanent freshwater habitats: shallow wetlands, stagnant waters, marshes, streams, rivers, ditches, canals, lakes, reservoirs, and ponds
Tolerant of cold climates (hibernate in bottom substrates when temperatures fall below freezing)
Central and eastern United States and the southern portions of Ontario and Quebec
North American Distribution
Introduced to many areas in the western United States; also introduced into Hawaii
Probable Means of Introduction
Intentional stocking as a food
Intentional stocking as a biocontrol agent of arthropod pests
Accidental introduction during fishery (e.g., trout) stocking
Bullfrogs are predators that eat practically anything that they can catch and swallow, including terrestrial and aquatic invertebrates (particularly crayfish), fish, other frogs, turtles, snakes, birds, mammals, etc.
Introduced bullfrogs have been blamed for native species declines in much of western North America.
Primary or suspected factor in declines of native species in western states, including leopard frogs and garter snakes in southern Arizona, leopard frogs in New Mexico, amphibians (e.g., red-legged frogs), reptiles (e.g., Western pond turtle) and fish in California and Oregon.
Used as food source for humans
Introduced to control pest species (e.g., Japanese beetles in Hawaii)
Removal, including regulated harvests
Introduction of predator species (e.g., largemouth bass)
Prohibit intentional stocking
Bury, R. B., and J. A. Whelan. 1984. Ecology and management of the bullfrog. U.S. Fish and Wildlife Service Resour. Publ. 155. 23 pp.
Conant, R., and J. T. Collins. 1991. Reptiles and Amphibians. Eastern/Central North America. Houghton Mifflin Company. Boston. 450 pp.
Hayes, M. P. and M. R. Jennings. 1986. Decline of ranid frog species in western North America: are bullfrogs (Rana catesbeiana) responsible? Journal of Herpetology 20:490-509.
Leonard, W. P., H. A. Brown, L. L. C. Jones, K. R. McAllister, and R.M. Storm. 1993. Amphibians of Washington and Oregon. Seattle Audubon Society, Seattle, WA. 168 pp.
Schwalbe, C. R., and P. C. Rosen. 1988. Preliminary report on effects of bullfrogs on wetland herpetofauna in southeastern Arizona. Pages 166-173 in R. C. Szaro, K. E. Severson, and D.R. Patton eds. Management of amphibians, reptiles, and small mammals in North America. U.S. Forest Service Gen. Tech. Rep. RM-166, Fort Collins, CO.
Vial, J. L., and L. Saylor. 1993. The status of amphibian populations: a compilation and analysis. International Union for the Conservation of Nature and Natural Resources, Species Survival Commission, Declining Amphibian Populations Task Force Working Document 1. 98 pp.
Bullfrogs: Introduced Predators in Southwestern Wetlands
Introduced species of Hawaii
Impact of invasive exotic animals on native reptiles and amphibians