American Bullfrog Facts

The American bullfrog belongs to the family Ranidae, the true frogs, within the genus Lithobates (formerly classified under Rana in older literature). It is closely related to other North American true frogs such as the green frog and pickerel frog, but is markedly larger than most of its relatives.

The species is named for naturalist Mark Catesby, who documented much of the flora and fauna of the American Southeast in the 18th century. Bullfrogs evolved as large, generalist predators suited to permanent freshwater habitats across the eastern half of the continent.

Adult bullfrogs typically measure 3.5 to 6 inches (9 to 15 cm) in body length, with large individuals occasionally approaching 8 inches (20 cm). Weight ranges from a fraction of an ounce in juveniles to as much as 1.5 pounds (0.5 kg) in the largest adults. Coloring is mottled green to brown, providing camouflage against pond vegetation and mud.

A key identifying feature is the tympanum, the external eardrum, visible as a large circular patch behind each eye; in males it is noticeably larger than the eye itself. Bullfrogs lack the dorsolateral ridges (raised skin folds) found on many other North American frogs, giving their back a smoother profile. Powerful, muscular hind legs with extensively webbed feet drive both jumping and swimming.

Bullfrogs live in wetland habitats with permanent standing water, including ponds, lakes, marshes, and slow-moving stretches of streams and rivers. They favor sites with soft, muddy banks and dense vegetation for cover, and readily colonize artificial waters such as reservoirs, farm ponds, and drainage ditches.

Their native range covers eastern North America, from southern Canada and the Great Lakes region south through the central and eastern United States into northeastern Mexico. Since the early 20th century, bullfrogs have been introduced far beyond this range — to the western United States, and to countries including Belgium, France, Italy, South Korea, Japan, China, Taiwan, Brazil, and Colombia — mostly through deliberate releases tied to the frog-leg food trade and the pet and bait trades. In these introduced regions, bullfrogs are established as breeding populations rather than occasional escapees.

Bullfrogs are opportunistic carnivores that eat almost any animal small enough to swallow. Prey includes insects, crayfish, small fish, other frogs, small snakes, small birds, and small mammals; there are even documented cases of bullfrogs catching bats at the water's surface. This unusually broad diet, combined with a willingness to eat other frog species — including smaller members of their own species — makes them effective and disruptive predators wherever they are established.

Hunting follows a sit-and-wait pattern. A bullfrog positions itself at the water's edge or partly submerged, remains motionless, and lunges with its wide mouth when prey comes within range. Most hunting activity occurs at night or during dawn and dusk hours.

Bullfrogs are largely solitary outside the breeding season and defend territories around favored basking and hunting sites, particularly males guarding stretches of shoreline. Males announce and defend territory with a deep, resonant call often described as sounding like "jug-o-rum," audible over long distances across open water.

Aggregations form during the breeding season, when males call from fixed positions to attract females and will grapple with rival males that intrude on a claimed territory. Bullfrogs are largely nocturnal and crepuscular, most active from dusk through the night.

Breeding occurs in spring and summer once water temperatures warm sufficiently. A female lays her eggs in a large surface film on the water, with a single clutch commonly containing 2,000 to 20,000 eggs — among the largest clutch sizes of any North American frog. Eggs hatch within about three to five days into tadpoles.

The tadpole stage is unusually long for a frog. In warm climates, tadpoles can complete metamorphosis into froglets within about a year, but in colder regions development can stretch to two or three years before the tadpole transforms. This extended larval period is one of the species' most distinctive traits and contributes to its ecological footprint, since tadpoles themselves compete with and are preyed upon by other aquatic wildlife for extended periods. Once mature, bullfrogs typically live 7 to 9 years in the wild and can reach 16 years in captivity.

(Population and conservation trend data sourced from the IUCN Red List of Threatened Species)

The American bullfrog is classified as Least Concern, with a population trend listed as Increasing. Within its native eastern North American range, populations are generally stable and the species faces the ordinary pressures of wetland habitat loss and water pollution.

The larger conservation concern runs in the opposite direction: outside its native range, the bullfrog is regarded as a harmful invasive species. Introduced populations prey heavily on native frogs, tadpoles, invertebrates, and small vertebrates, and can outcompete native amphibians for food and breeding sites. Bullfrogs are also implicated in spreading amphibian chytrid fungus (Batrachochytrium dendrobatidis) to native frog populations that lack resistance to it. Several countries and regions, including parts of the European Union, restrict or prohibit the keeping, sale, and release of American bullfrogs specifically because of this invasive impact.

• IUCN Red List of Threatened Species: Lithobates catesbeianus
• USGS Nonindigenous Aquatic Species: Lithobates catesbeianus
• AmphibiaWeb: Lithobates catesbeianus
• National Geographic: American Bullfrog