The American bullfrog (Lithobates catesbeianus), often simply known as the bullfrog in Canada and the United States, is a species of large frog in the family Ranidae (true frogs). The species is native to eastern North America. It typically inhabits large permanent water bodies such as swamps, ponds, and lakes. The bullfrog can also be found in manmade habitats such as pools, koi ponds, canals, ditches, reservoirs and culverts. The bullfrog gets its common name from the sound the male makes during the breeding season, which sounds similar to a bull bellowing. It is a generalist carnivore, consuming a wide variety of prey. In turn, it is eaten by predators such as alligators, snakes, and birds.
The bullfrog is large and is commonly eaten by humans throughout its range, especially in the southern United States where it is plentiful. Its use as a food source has led to the bullfrog being introduced outside of its native range. The bullfrog has been introduced in more than 40 countries and many continents including the Western United States, the Caribbean, South America, Western Europe, Belgium, Italy, Spain, Greece, China, Japan, South Korea, Malaysia, Southeast Asia, and more. In these places it is considered an invasive species due to its voracious appetite and the large number of eggs it produces, which has a negative effect on native amphibians, certain insects and other fauna. The bullfrog is very skittish, which can make its capture difficult, and thus it often becomes established.
Other than for food, the bullfrog is also used for dissection in science classes. Albino bullfrogs are sometimes kept as pets, and bullfrog tadpoles are often sold at ponds or fish stores.
Taxonomy and etymology The specific name, catesbeiana (feminine) or catesbeianus (masculine), is in honor of English naturalist Mark Catesby.Feduccia, Alan (editor) (1985). Catesby's Birds of Colonial America. Chapel Hill, North Carolina: University of North Carolina Press. 208 pp. . (Rana catesbeiana, Preface, p. xiii). Some authorities use the scientific name, Lithobates catesbeianus, although others prefer Rana catesbeiana.
Cladogram of the position of the American bullfrog within Lithobates, after Martínez‐Gil et al. 2025:
Description The dorsal (upper) surface of the bullfrog has an olive-green background color, either plain or with mottling and banding of grayish brown. The ventral (under) surface is off-white blotched with yellow or gray. Often, a marked contrast in color is seen between the green upper lip and the pale lower lip. The teeth are tiny and are useful only in grasping. The eye is prominent with a brown iris and a horizontal, almond-shaped pupil. The tympanum (eardrum) is easily seen just behind the eye, and a dorsolateral fold of skin encloses it. The limbs are blotched or banded with gray. The fore legs are short and sturdy, and the hind legs are long. The front toes are not webbed, but the back toes have webbing between the digits with the exception of the fourth toe, which is unwebbed.
The bullfrog is sexually dimorphic, with males being smaller than females and having yellow throats. Males have tympana larger than their eyes, whereas the tympana in females are about the same size as the eyes. Bullfrogs measure about in snout–to–vent length. They grow fast in the first eight months of life, typically increasing in weight from , and large, mature individuals can weigh up to . In some cases bullfrogs have been recorded as attaining and measuring up to from snout to vent. The American bullfrog is the largest species of true frog in North America.
Geographic distribution
The bullfrog is originally native to eastern North America, where it is commonly found in every U.S. state east of the Mississippi River. Its natural range extends from the eastern Canadian Maritime Provinces to as far west as Idaho and Texas, and as far north as Michigan (including the Upper Peninsula), Minnesota and Montana; it is largely absent in North Dakota.
Within North America, the bullfrog has been introduced to Nantucket island, as well as portions of the western U.S., including Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming. In these states, it is considered to be an invasive species, as concerns exist that it may outcompete or prey upon native species of reptiles and amphibians, disrupting the delicate ecological balance of certain areas. It is very common on the West Coast, especially in California, where it is believed to pose a threat to the California red-legged frog, and is considered to be a factor in the decline of that vulnerable species. Bullfrogs have been found to feed on the young of several snakes, including the California endemic giant garter snake, a threatened species. In early 2023, the Utah Department of Natural Resources began tweeting tips on how to catch and cook bullfrogs in an effort to encourage residents to help control the growing population by catching the invasive frogs for food.
The bullfrog has also been introduced to Hawaii, South America, Asia, the Caribbean, and Europe for various purposes including frog farming and population control of other species.Both, Camila, et al. "Widespread occurrence of the American bullfrog, Lithobates catesbeianus (Shaw, 1802)(Anura: Ranidae), in Brazil." South American Journal of Herpetology 6.2 (2011): 127-134. Specifically, the bullfrog has been introduced to the extreme south of British Columbia, Canada, nearly every state in Mexico, as well as Belgium, Cuba, the Dominican Republic, Haiti, Italy, Jamaica, the Netherlands, and Puerto Rico. It is also found in Argentina, Brazil, China, Colombia, Japan, South Korea, Uruguay and Venezuela. The reasons for introducing the bullfrog to these areas have largely been intentional, either to provide humans with a source of food or as biological control agents. In addition, the unintended escape of frogs from breeding establishments or scientific research facilities, captive escapees or released pets are also a possibility. Conservationists are concerned that the bullfrog is relatively immune to the fungal infection chytridiomycosis (also called 'chytrid' fungus) which has been ravaging numerous frog species: as it invades new territories, it may assist in the spread of this lethal fungus as an asymptomatic carrier, spreading the fungus to more susceptible, native species of frog it encounters.
Biology Ecology The bullfog is a voracious, opportunistic, ambush predator that preys on any small animal it can overpower and consume. Bullfrog stomachs have been found to contain rodents, small lizards and snakes, other frogs and toads, other amphibians, crayfish, other crustaceans, small birds, scorpions, tarantulas and bats (such as big brown bats, eastern red bats, southeastern myotis, and other unidentified bats), as well as the many types of invertebrates, such as snails, worms and insects, which are the usual food of ranid frogs. These studies revealed the bullfrog's diet to be unique among North American ranids in the inclusion of a large percentage of aquatic animals, such as fish, tadpoles, ram's horn snails, and dytiscid beetles, as well as the aquatic eggs of fish, frogs, insects, or salamanders. Cannibalism has been observed in bullfrog populations in resource-limited environments.Leivas, P. T., Leivas, F. W., & Moura, M. O. (2012). Diet and trophic niche of Lithobates catesbeianus (Amphibia: Anura). Zoologia (Curitiba), 29, 405-412. The bullfrog is able to capture large, strong prey because of the powerful grip of its jaws after the initial ranid tongue strike. However, there is a correlation found with size of prey relative to body size of the bullfrog. Juveniles and adults typically go after prey that is relative to their own body size.Ortíz-Serrato, Liliana, et al. "Diet of the Exotic American Bullfrog, Lithobates Catesbeianus, in a Stream of Northwestern Baja California, Mexico." Western North American Naturalist, vol. 74, no. 1, 2014, pp. 116–22, https://doi.org/10.3398/064.074.0112. The bullfrog is able to make allowance for light refraction at the water-air interface by striking at a position posterior to the target's perceived location. The comparative ability of the bullfrog to capture submerged prey, compared to that of the green frog, leopard frog, and wood frog (Lithobates clamitans, Lithobates pipiens, and Lithobates sylvaticus, respectively) was also demonstrated in laboratory experiments.
Prey motion elicits feeding behavior. First, if necessary, the frog performs a single, orienting bodily rotation ending with the frog aimed towards the prey, followed by approaching leaps, if necessary. Once within striking distance, the bullfrog begins its feeding strike, which consists of a ballistic lunge (eyes closed as during all leaps) that ends with the mouth opening. At this stage, the fleshy, mucus-coated tongue is extended towards the prey, often engulfing it, while the jaws continue their forward travel to close (bite) just as the tongue is retracted. Large prey that do not fit entirely into the mouth are stuffed in with the hands. In laboratory observations, bullfrogs taking mice usually swam underwater with prey in mouth, apparently with the advantageous result of altering the mouse's defense from counter-attack to struggling for air. Asphyxiation is the most likely cause of death of warm-blooded prey.
The bullfrog is an important item of prey for many birds (especially large herons), the North American river otter (Lontra canadensis), predatory fish, and occasionally other amphibians. Predators of the American bullfrog once in its adult stage can range in weight from belted kingfishers (Megaceryle alcyon) to American alligators (Alligator mississippiensis). The eggs and larvae are unpalatable to many salamanders and fish, but the high levels of activity of the tadpoles may make them more noticeable to a predator not deterred by their unpleasant taste. Humans hunt bullfrogs as game and consume their legs. Adult frogs try to escape by splashing and leaping into deep water. A trapped individual may squawk or emit a piercing scream, which may surprise the attacker sufficiently for the frog to escape. An attack on one bullfrog is likely to alert others in the vicinity to danger and they will all retreat into the safety of deeper water. Bullfrogs may be at least partially resistant to the venom of copperhead (Agkistrodon contortrix) and cottonmouth (Agkistrodon piscivorus) snakes, though these species are known natural predators of bullfrogs as are northern water snakes (Nerodia sipedon).Conant, Roger. (1975). A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Second Edition. Houghton Mifflin Company, Boston.
As an invasive species Multiple traits of L. catesbeianus contribute to its competitive ability, especially as an invasive. The generalist diet of the American bullfrog allows for it to consume food in different environments. They directly predate indigenous frog species, leading to numerous frog declines. When observing the contents of American bullfrog stomachs, it was discovered that adult bullfrogs regularly consume predators of bullfrog young, including dragonfly nymphs, garter snakes, and giant water bugs. Thus, the ecological check on American bullfrog juveniles in invaded areas become less effective. L. catesbeianus seems to exhibit traits of immunity or resistance against the antipredator defenses of other organisms, with analysis of stomach contents from New Mexican bullfrogs showing the regular consumption of wasps, with no conditioned avoidance due to the wasps' stingers. Along the Colorado river, L. catesbeianus stomach contents indicate the ability to withstand the discomforting spines of the stickleback fish. Reports of American bullfrogs eating scorpions and rattlesnakes also exist.