The American bullfrog is active both by day and night (5). As with many other amphibians, this species produces a toxin in its skin which makes it distasteful to most vertebrate predators (4).
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 tadpoles and young adults of the American bullfrog are mostly herbivorous, and feed on algae and other plant material, although they also sometimes take small aquatic invertebrates (3) (4) (5).
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).
Tadpoles of this species are able to overwinter in water under a cover of ice (5), while adults tend to hibernate in mud when the weather becomes cold (3) (4) (5) (6).