American Bullfrog Facts

Adults usually run 3.5 to 6 inches in body length, with big individuals nearing 8 inches and up to about 1.5 pounds. The mottled green-to-brown skin blends into pond mud and weed. The clearest identifier is the tympanum — the round external eardrum behind each eye; in males it is noticeably larger than the eye itself, while in females it is about the same size. Bullfrogs lack the raised dorsolateral skin ridges of many other North American frogs, so the back looks smooth, and powerful, fully webbed hind legs drive both long jumps and strong swimming. They belong to the true-frog family Ranidae and are named for the 18th-century naturalist Mark Catesby.

Bullfrogs need wetland with permanent standing water — ponds, lakes, marshes, and slow river reaches — and favour soft muddy banks and dense cover, readily taking to reservoirs, farm ponds, and ditches. Their native range covers eastern North America from southern Canada and the Great Lakes south into northeastern Mexico. Since the early 20th century they have been introduced far beyond it — the western U.S. and countries from France and Italy to Japan, China, Brazil, and Colombia — mostly through deliberate releases tied to the frog-leg, pet, and bait trades, where they now breed as established populations rather than stray escapees.

Bullfrogs are opportunistic carnivores that will eat almost anything they can swallow: insects, crayfish, small fish, other frogs, small snakes, small birds, and small mammals — there are even records of them snatching bats at the water's surface. That enormous, indiscriminate appetite, and a readiness to eat other frogs including smaller bullfrogs, is exactly what makes them so disruptive where they are introduced. Hunting is sit-and-wait: the frog holds still at the water's edge or half-submerged and lunges with its wide mouth, mostly at night and in the dim hours around dawn and dusk.

Outside breeding, bullfrogs are largely solitary, and males in particular defend stretches of shoreline around prime basking and hunting spots. The territorial call is a deep, resonant "jug-o-rum" that carries far across open water. In the breeding season, males call from fixed positions to attract females and will grapple with rivals that intrude on a claimed patch. They are chiefly nocturnal and crepuscular, most active from dusk through the night.

Breeding runs through spring and summer once the water warms. The female lays her eggs as a large film on the surface, a single clutch often holding 2,000 to 20,000 eggs — among the biggest of any North American frog — and they hatch in three to five days. The tadpole stage is unusually long: in warm climates it may finish metamorphosis within a year, but in colder regions development can stretch to two or three years. That extended larval life is a defining trait and part of the species' ecological footprint, since the tadpoles compete with and prey on other pond wildlife for a long time. Adults typically live 7 to 9 years in the wild, and up to 16 in captivity.

In its native eastern range the bullfrog is Least Concern with an increasing trend, facing only the ordinary pressures of wetland loss and water pollution. The real conservation story runs the other way: outside that range it is a damaging invasive. Introduced bullfrogs prey heavily on native frogs, tadpoles, invertebrates, and small vertebrates, outcompete native amphibians for food and breeding sites, and are implicated in spreading the amphibian chytrid fungus (Batrachochytrium dendrobatidis) to species with no resistance to it. Several countries and regions — including parts of the European Union — restrict or ban keeping, selling, and releasing them for exactly this reason.

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