Amphibians
Bullfrog
Lithobates, Pyxicephalus, and others · also called bull frog
A bullfrog is not one animal. On several continents, evolution has independently produced the same thing: a huge frog with a booming call and a mouth that will close on anything it can fit, from a dragonfly to a duckling. The American and African versions are only distant relatives, but they live almost identical lives.
Overview
“Bullfrog” is a common name for large, loud, predatory frogs in several unrelated families. The main ones are the American bullfrog (Lithobates, the true frog family), the African bullfrog (Pyxicephalus), and the Indian bullfrog, with other frogs called bullfrogs in South America and Australia. All are carnivores that sit at the water’s edge and lunge at prey, stuffing it down with the forelimbs and their retracting eyeballs.
The call
Male bullfrogs produce a deep, low bellowing call through large paired vocal sacs — the American bullfrog’s carries more than a kilometre across still water — to hold a territory they defend with wrestling matches.
Devoted, and drought-proof
A male African bullfrog guards the eggs and tadpoles, and will dig channels to drain water from a nearby pool to keep a drying nursery alive. The African and Indian bullfrogs and others burrow deep and cocoon themselves in shed skin, waiting out the dry season for months or, for the African bullfrog, possibly years.
The invader
The American bullfrog, spread worldwide by the frog-leg and pet trades, is one of the most damaging invasive amphibians — eating native frogs, fish, and reptiles, out-competing local wildlife, and carrying the chytrid fungus and ranavirus without harm to itself.
Status
Bullfrog is not a species and is Not Evaluated as one. The American bullfrog is abundant and invasive; the African bullfrog is declining in South Africa from wetland loss and roadkill on its breeding migrations; the Indian bullfrog was reduced by past frog-leg harvesting before trade controls.
Bullfrog: common questions
Is there one bullfrog or many?
Many. Bullfrog is a common name applied independently to large, loud, predatory frogs in several parts of the world, and the animals so called are not closely related. The American bullfrog belongs to the true frog family and the genus Lithobates. The African bullfrog is in a different family and the genus Pyxicephalus. The Indian bullfrog, the South American bullfrog, and Australia's giant frog are others again. What unites them is a body plan and a lifestyle — a heavy body, a wide mouth, a deep booming call, and a habit of sitting still at the water's edge and lunging at anything edible that comes near.
How big does a bullfrog get, and what can it eat?
The American bullfrog reaches about 20 cm from snout to vent, not counting the legs, and 500 g or more. The African bullfrog is bulkier, up to around 24 cm and 1.4 kg, one of the largest frogs in the world. Both have a gape wide enough to attempt prey close to their own size. Documented bullfrog meals include other frogs, small snakes, mice, bats snatched at the water surface, ducklings, small turtles, and fish, alongside the usual insects and crayfish. A bullfrog does not chew; it uses its eyes, which retract into the head, to help push large prey down its throat.
Why are American bullfrogs a problem outside North America?
The American bullfrog is large, long-lived, and enormously fecund, with a single female laying up to 20,000 eggs, and outside its native range it usually meets no effective predators or competitors. Introduced through the frog-leg and pet trades and by deliberate stocking, it has established across the western United States and in parts of Europe, South America, and Asia, where it eats native amphibians, fish, snakes, and hatchling birds, and out-competes local species for food and breeding sites. Bullfrogs also frequently carry the amphibian chytrid fungus and ranavirus without falling ill, so they act as reservoirs that can trigger disease outbreaks in more vulnerable native species.
How does the African bullfrog survive the dry season?
It goes underground and waits, sometimes for a very long time. As its wetland dries after the rains, the frog uses hardened tubercles on its hind feet to dig backward into the soil, often more than a foot down, and settles into a chamber. Its skin glands then secrete mucus that dries into a tough, semi-transparent cocoon enclosing the whole body except the nostrils, drastically slowing water loss. Sealed in this state its metabolism drops to a crawl and it lives on stored fat and reabsorbed water held in its bladder. It can remain dormant through an entire dry season and, by some accounts, survive more than one year buried before rain soaks through and triggers it to dig out.