Amphibians
African Bullfrog
Pyxicephalus adspersus · also called pixie frog, giant bullfrog, South African burrowing frog
The African bullfrog is a frog built like a bull terrier — squat, enormously wide-mouthed, and startlingly aggressive. It is among the largest frogs alive, it eats vertebrates as readily as insects, it guards its tadpoles against all comers, and it can sleep through years of drought sealed in a cocoon of its own skin.
Overview
African bullfrogs live in savanna, grassland, and seasonal wetlands across southern and eastern Africa, anywhere with soft soil to dig in and shallow pools that fill during the summer rains. For most of the year they are invisible, buried underground. They surface with the rains to feed and breed, and spend the rest of the time as ambush hunters half-sunk in mud at the edge of a pool.
An enormous appetite
The bullfrog is a sit-and-wait carnivore with a gape that runs the full width of its head and blunt bony pseudo-teeth on the lower jaw for holding struggling prey. It takes insects, scorpions, other frogs, snakes, lizards, small turtles, rodents, and nestling birds, and it is entirely willing to attack prey too large to actually swallow. Cannibalism is common, and males will eat the tadpoles of rival males.
Breeding battles
Breeding is explosive and violent. After heavy rain, hundreds of bullfrogs converge on a temporary pool for just a few days. Large males fight in the shallows — wrestling, biting, and inflating their bodies — for the central positions where females prefer to spawn, and these fights sometimes end in a death. Females lay several thousand eggs, which hatch within days.
The guarding father
Once the eggs hatch, the male stands guard over the writhing black mass of tadpoles, lunging at herons, monitor lizards, and any other threat, and reportedly even at elephants and lions that come to drink. If the tadpole pool is drying out, the male will dig an irrigation channel with his body to let water in from a deeper pool nearby — a remarkable piece of behaviour for an amphibian.
Surviving drought
When the pools vanish, the bullfrog burrows down and encases itself in a cocoon of shed skin that hardens into a waterproof envelope, with only its nostrils open. It can remain like this through the dry season, or for years if rain does not come, living off stored water and fat. A thunderstorm soaking the ground wakes it.
Status
The African bullfrog is listed as Least Concern and remains widespread, but populations are declining locally from wetland drainage, road building across breeding routes, pollution, and collection for food and the pet trade. In parts of South Africa it is a protected species, and urban breeding sites are sometimes fenced and managed to get the frogs safely across roads to their pools.
African Bullfrog: common questions
How big does an African bullfrog get?
Large males can reach around 24 centimetres from snout to vent — roughly the length of a dinner plate — and weigh well over a kilogram, making this one of the two or three largest frogs on the planet, alongside the goliath frog of West Africa. There is extreme size difference between the sexes here — unusually, the males are the giants, sometimes three times the weight of a female, because males fight for breeding territories.
What does an African bullfrog eat?
More or less anything that moves and fits in its very wide mouth. The diet includes large insects, scorpions, other frogs (including its own kind), lizards, snakes, small turtles, mice and rats, and small birds. There are documented cases of captive bullfrogs eating dozens of newly hatched cobras, and one famous account of a wild bullfrog attempting to swallow a whole brood of young birds. It hunts by sitting still, partly buried, and lunging.
How does the African bullfrog survive the dry season?
When its seasonal pools dry up, the frog digs backwards into the soil using hardened tubercles on its hind feet, then sheds successive layers of skin that harden into a nearly waterproof cocoon around its whole body, leaving only the nostrils clear. Inside this bag it drops its metabolism drastically and waits — normally for the months of the dry season, but it can stay dormant for several years if the rains fail, reabsorbing its own bladder water to stay hydrated. The first heavy storms trigger it to dig out.
Do African bullfrogs really guard their young?
Yes, and aggressively — parental care is rare among frogs and striking in one this size. After eggs are laid in a shallow pool, the male stays with the developing eggs and then the mass of tadpoles, driving off predators many times his size. If the tadpole pool starts to dry or overheat, he has been filmed digging a channel with his body to release water from a larger pool into the nursery. Herpetologists working near a guarding male are routinely bitten and lunged at.