Sunday 19 May
American bullfrog (Lithobates catesbeiana)
- The American bullfrog is North America’s largest frog species.
- The American bullfrog is named for its deep, resonant croak.
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American bullfrog fact file
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American bullfrog description
This impressive, golden-eyed amphibian has a broad head and body (6), and its rough skin is covered in tiny, randomly arranged tubercles (2). The tips of the American bullfrog’s fingers and toes are blunt, and the webbing between the digits is well developed (2).
The colouration of the American bullfrog varies widely depending on the location (2) (7), with its upperparts ranging from bright green to olive or brownish green (3) (4) (5). A netlike pattern of brown or grey markings may be present on its back (2). The hind limbs are long and powerful (7) and have dark blotches and bands (5). The underside of the American bullfrog is much paler than the upperparts (3), with a cream or whitish belly (3) (5) that is tinged with yellow or mottled with grey (2) (3).
As well as being larger than the male (5), the female American bullfrog is also generally browner and more highly spotted (3). The throat of the male is yellow, while that of the female is white (5) (6), and a further difference between the sexes is the presence of pigmented ‘nuptial pads’ on the thumbs of the male, which are used to grip the female during mating (2).
As with the adults, the tadpoles of the American bullfrog are large (4) (5). The back of the tadpole is yellowish green, speckled with black spots, and has an arched dorsal fin, while the belly is lighter (5).
- Also known as
- Bullfrog, Common bullfrog.
- Male length: 11.1 - 17.8 cm (2)
- Female length: 12 - 18.3 cm (2)
- Tadpole length: 4 - 15 cm (3) (4)
- 0.5 kg (4) (5)
IUCN/SSC Amphibian Specialist Group:
Gascon, C., Collins, J.P., Moore, R.D., Church, D.R., McKay, J.E. and Mendelson III, J.R. (2005) Amphibian Conservation Action Plan. The World Conservation Union (IUCN), Gland, Switzerland. Available at:
- Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- Feeding on flesh.
- Dorsal fin
- The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans (whales, dolphins and porpoises).
- Having a diet that comprises only vegetable matter.
- A winter survival strategy in which an animal’s metabolic rate slows down and a state of deep sleep is attained. While hibernating, animals survive on stored reserves of fat that they have accumulated in summer.
- Animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones) and echinoderms.
- An abrupt physical change from the larval to the adult form.
- An area occupied and defended by an animal, a pair of animals or a group.
- A small, rounded, wart-like bump on the skin or on a bone.
- An animal with a backbone, including mammals, birds, reptiles, amphibians and fish.
IUCN Red List (May, 2012)
AmphibiaWeb - Rana catesbeiana (May, 2012)
- Marshall Cavendish (2010) North American Wildlife. Marshall Cavendish Reference, New York.
- Boersma, P.D. and Van Buren, A.N. (2006) Invasive Species in the Pacific Northwest. University of Washington Press, Washington.
- Woodward, S.L. and Quinn, J.A. (2011) Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels, Volume 1. ABC-CLIO, Santa Barbara.
- Day, L., Klingler, M.A. and Bloomberg, M.R. (2007) Field Guide to the Natural World of New York City. Johns Hopkins University Press, Baltimore.
- Burnie, D. (2011) Animal. Dorling Kindersley Ltd., London.
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American bullfrog biology
The American bullfrog is a carnivorous amphibian (3) (4) (5) (6) and has a voracious appetite (4), consuming almost anything it can fit in its mouth and swallow (4) (6). It is an opportunistic predator (2) (3) and has a very varied diet, consisting of insects, earthworms, crayfish, spiders and snails (2) (3) (5). The American bullfrog catches prey using its large, sticky tongue (5), after lying in wait for its victim (3). It also consumes larger prey, including snakes, birds, turtles and frogs, as well as bats and other small mammals (3) (5) (6), and it has even been known to catch swallows flying low over the water (3). Cannibalism is prevalent in the American bullfrog, with other individuals of the same species thought to constitute up to 80 percent of its diet (2).
The breeding season of the American bullfrog starts in the spring, and continues throughout early summer. However, timings can vary somewhat depending on latitude (2), with breeding occurring from May to July in northern states, and from February to October in warmer regions (5). Males defend territories during the breeding season, and use their vocal sacs to produce a deep, sonorous call to attract mates (7). This distinctive booming call, which can be heard from almost a kilometre away (3), consists of a single note (2) and is often reported to sound like ‘jug-o-rum’ (3) (4) (5) (6). The male American bullfrog moves out into open water to call, while the female stays inshore. The female will only join the male once she is ready to lay eggs (3).
After mating, the female lays between 10,000 and 25,000 eggs (3) (6), with the size of the clutch being dependent on the size of the female (3). A clutch normally consists of one quarter of the female’s body weight (2). The eggs are jelly-coated (5) (6) and float in a film on the surface of the water (3) (4), creating a ‘raft’ which can reach a metre in diameter (5). Not long before hatching, the mass of eggs sinks (4) (5). Hatching occurs within a week of the eggs being laid (3) (4) (6), but the tadpoles can take up to two years to undergo metamorphosis (3) (4) (6), depending on the temperature of their environment (2).Top
American bullfrog range
However, this species has also been introduced to western parts of the United States (3), as well as certain regions of Europe, South America, eastern Asia and the Caribbean (4) (5) (7). In some areas, introductions were made to produce frogs’ legs as a source of food (2) (4).Top
American bullfrog habitat
In all stages of its lifecycle (4), the American bullfrog is found in permanent freshwater ponds and lakes (4) (6) (7). Still waters are generally preferred (4) (5), although the American bullfrog is also often found in slow-moving streams (3) (5) (6) (7).
The American bullfrog favours bodies of water in lowlands (4), particularly shallow areas (5) where aquatic vegetation is abundant (3) (5). The tadpoles of this species, however, tend to prefer non-vegetated water bodies (5).
Cold or dry areas are usually avoided (4), as the American bullfrog requires warm water for breeding (5). This species has a higher tolerance than many other native amphibians for the elevated water temperatures often found in human-modified environments (4).Top
American bullfrog status
The American bullfrog is classified as Least Concern (LC) on the IUCN Red List (1).Top
American bullfrog threats
Other than being farmed and hunted for human consumption in some areas (4) (5) and being predated upon by raccoons, snakes and some wading birds (4) (6), the American bullfrog is not currently facing any major threats. In fact, its introduction to areas outside of its natural range has threatened many native species, particularly other amphibians, either through predation or competition (2) (4) (5). As a result, the American bullfrog poses a serious challenge to conservation efforts in many regions (4), and it has been classed by IUCN’s Invasive Species Specialist Group as one of the 100 worst invasive species in the world (5).
There are also concerns that the American bullfrog may be a carrier of the chytrid fungus, which it appears to be somewhat resistant to, but which is deadly to many other amphibian species (2).
The American bullfrog is able to travel relatively long distances overland during rainy periods (4). This, combined with the ease with which juveniles colonise new ponds (2), leads to recolonisation occurring quickly, even where eradication programmes have been implemented. This makes American bullfrog populations very difficult to control (4).Top
American bullfrog conservation
Given that the American bullfrog is not threatened, there are currently no conservation measures aimed specifically at this species.Top
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