Head to head
American Bullfrog vs African Bullfrog
Two big frogs, two continents, one shared name and almost nothing else in common. The American bullfrog and the African bullfrog belong to different families that are not close relatives, and they solve the problems of frog life in very different ways. One stays in the water and spreads around the world as a pest; the other buries itself for months and guards its young.
| American Bullfrog | African Bullfrog | |
|---|---|---|
| Scientific name | Lithobates catesbeianus | Pyxicephalus adspersus |
| Family | True frogs (Ranidae) | African bullfrogs (Pyxicephalidae) |
| Native range | Eastern and central North America | Savanna and grassland of southern and eastern Africa |
| Size | About 15 to 20 cm; up to around 500 g | Up to about 24 cm and over 1 kg; males larger than females |
| Lifestyle | Aquatic, at the edges of ponds and lakes year-round | Spends much of the year buried in a mucus cocoon |
| Breeding | Males hold calling territories; tadpoles take 1 to 3 years | Explosive breeding in rain pools; male guards eggs and tadpoles |
| Temperament | Wary; flees into water | Aggressive; bites hard and lunges at threats |
| Status as an invader | Major invasive species on several continents | Not invasive; stays within its range |
American Bullfrog vs African Bullfrog: common questions
Are the American and African bullfrogs related?
No more than most frogs are. They sit in different families, the true frogs for the American bullfrog and the African bullfrogs for the African one, and those families diverged tens of millions of years ago. The shared name simply reflects the fact that early English speakers on both continents called any large, deep-voiced frog a bullfrog. The two look superficially alike in being big and blunt-headed, but the African bullfrog is squatter and more heavily built, has prominent skin ridges, and its males dwarf its females, which is the reverse of the usual frog pattern and of the American bullfrog, where females are the larger sex.
How does the African bullfrog survive the dry season?
It goes underground and seals itself in. As the rains end, the frog digs backward into soft soil using hardened tubercles on its hind feet, then sheds successive layers of skin that harden around it into a nearly waterproof cocoon, leaving only the nostrils open. Inside this casing its metabolism drops and it can wait out the dry months, and in a severe drought it may stay buried for a year or more, living off stored fat and reabsorbing water from its own urine. When rain finally soaks the ground, the frog breaks out of the cocoon, digs to the surface, and heads for the newly filled pools to feed and breed within days.
Why is the American bullfrog such a problem outside North America?
It is large, hardy, hungry, and highly fertile. A female can lay up to 20,000 eggs at once, the tadpoles are distasteful to many predators, and the adults eat any animal that fits in the mouth, so where bullfrogs are introduced they tend to eat and outcompete smaller native frogs, fish, reptiles, and invertebrates. They also tolerate disturbed and modified habitats well. On top of the direct predation, bullfrogs frequently carry the amphibian chytrid fungus without being harmed by it, acting as a reservoir that can infect more vulnerable local species. Populations established from escaped or released farm and pet animals are now considered invasive in parts of Europe, South America, the Caribbean, and Asia, and in the western United States beyond the native range.