Ecology Bullfrogs are voracious, opportunistic,
ambush predators that prey on any small animal they 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, 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. Bullfrogs are able to capture large, strong prey because of the powerful grip of their 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. 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 bullfrogs to capture submerged prey, compared to that of the green frog, leopard frog, and wood frog (
L. clamitans, L. pipiens, and
L. sylvaticus, respectively) was also demonstrated in laboratory experiments. 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).
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. Analysis of the American bullfrog's realized niche at various sites in Mexico, and comparisons with the niches of endemic frogs show that it is possible that the American bullfrog capable of niche shift, and pose a threat to many endemic Mexican frog species, even those that are not currently in competition with the American bullfrog. Self-sustaining populations of American bullfrogs became established in the United Kingdom around 1999, where their introduction was likely due to accidental escapes and deliberate releases from captivity. These populations appear to be quite small, and are undergoing control by
Natural England as the species poses a threat to native amphibians. The American bullfrog has been known to spread the amphibian pathogen
Batrachochytrium dendrobatidis among populations that it has been introduced to.
Breeding season The bullfrog
breeding season typically lasts two to three months. Conversely, females have brief periods of sexual receptivity during the season. In one study, female sexual activity typically lasted for a single night and mating did not occur unless the females initiated the physical contact. The significance of forelimb sexual dimorphism allow males to remain in amplexus with the female for longer durations increasing their chance at reproductive success in the highly competitive mating environment. Females can deposit 1,000 - 40,000 eggs which hatch in 3 - 5 days. These male and female behaviors cause
male-male competition to be high within the bullfrog population and
sexual selection for the females to be an intense process. This may reflect a lesser number of predators in these locations. As they grow, they tend to move into deeper water. The tadpoles initially have three pairs of external gills and several rows of labial teeth. They pump water through their
gills by movements of the floor of their mouths, trapping bacteria, single-celled
algae,
protozoans, pollen grains, and other small particles on mucus in a filtration organ in their
pharynges. As they grow, they begin to ingest larger particles and use their teeth for rasping. They have downward-facing mouths, deep bodies, and tails with broad dorsal and ventral fins. Time to
metamorphosis ranges from a few months in the southern part of the range to 3 years in the north, where the colder water slows development. Maximum lifespan in the wild is estimated to be 8 to 10 years, but one frog lived for almost 16 years in captivity. ==Relation to humans==