The American bullfrog (Lithobates catesbeianus, historically Rana catesbeiana) is a large, semi-aquatic frog in the family Ranidae often called a "true frog." Adults are notable for their robust bodies, strong hind legs, and a deep, resonant call produced by males during the breeding season that inspired the common name "bullfrog." They occupy a range of freshwater habitats where open water and vegetated edges are available, and they are active mainly at night in many parts of their range. Bullfrogs are opportunistic predators and capable swimmers; their size and appetite distinguish them from many other North American amphibians.

Characteristics and life cycle

Bullfrogs are among the largest frogs native to North America. They have smooth skin, a green to brown dorsum, and a white or yellowish belly; tympanums (external eardrums) are prominent, especially in males. Diets are broad and include insects, other amphibians, small fish, crustaceans, and occasionally small birds or mammals. Reproduction takes place in standing water: females lay large floating masses of eggs that can number in the thousands. Tadpoles may spend many months up to more than a year developing before metamorphosis, and juveniles disperse from breeding sites when conditions permit. In the wild their lifespan is often short due to predation and disease; in captivity bullfrogs have lived a decade or more.

Behavior, habitat and ecology

Bullfrogs favor ponds, lakes, marshes, and slow-moving waters with abundant vegetation. They typically remain near the water's edge but will move overland when dispersing, seeking new habitats after heavy rains or when local conditions change. Males establish territories and produce the deep mating calls that carry over water. As generalist predators, bullfrogs can affect local food webs by preying on a wide range of animals; their feeding habits can reduce populations of invertebrates and smaller vertebrates. Natural predators include wading birds, larger fish, snakes, and mammalian predators.

Distribution, introductions, and impacts

Native to much of eastern and central North America, bullfrogs have been intentionally and accidentally introduced to many other regions worldwide, including parts of the western United States, South America, Asia, Europe, and various islands. Introductions have often been linked to the pet trade, live food markets, aquaculture, and deliberate releases. In nonnative areas they may become invasive: their large size, fast growth, and broad diet enable them to compete with and prey upon native amphibians and other wildlife. They can also transport pathogens and parasites that affect local amphibian populations.

Human uses, health issues, and conservation

People have long harvested bullfrogs for food (notably their legs), scientific study, and the pet trade. They are resilient in many landscapes and are currently assessed as Least Concern by the International Union for Conservation of Nature at a global scale, but local populations face threats from habitat loss, pollution, overharvesting, and disease. Bullfrogs are known carriers of pathogens such as the chytrid fungus and other agents that contribute to amphibian declines elsewhere. Management in areas where they are invasive may include habitat modification, trapping, and public education to limit releases.

Distinctive facts

  • Male bullfrogs produce a loud, low-pitched call used in mating and territorial displays.
  • Egg masses can contain thousands of eggs; developmental time from egg to frog varies with temperature and resource availability.
  • Because they consume a wide array of prey, bullfrogs can alter local food webs when introduced outside their native range.

Further reading and resources