African Bullfrog

Quick Take

• This frog goes by a name that sounds like it belongs to a fairy tale creature, and the reason why is stranger than you'd expect. See the 'pixie' name →
• The African bullfrog is one of the only frogs on Earth with teeth, and how it uses them reveals something deeply unsettling about its parenting style. Explore the odontodes →
• When conditions get brutal, this frog pulls off a survival trick that no amount of instinct alone can explain. Discover the survival cocoon →
• Male African bullfrogs sometimes fight to the death, but what happens right after the battle is completely at odds with their aggressive reputation. See post-battle paternal care →

The African bullfrog is one of the largest frogs on Earth, with the Goliath Frog being the largest. Also known as the Giant African Bullfrog, males can grow to 9.6 inches long and weigh more than 3 pounds. This bullfrog primarily lives in the central part of sub-Saharan Africa. It is a voracious eater and will swallow anything it can, but it is also popular as a pet. One notable characteristic of the bullfrog is the sound it makes when it is annoyed, which has been described as croaking, roaring, or bleating.

4 Incredible African Bullfrog Facts

• Interestingly, the frog is also called the pixie frog—not, as one might assume, because of its size. “Pixie” comes from its scientific name, Pyxicephalus adspersus.
• As belligerent as he can sometimes be, the male African bullfrog is a doting father, to an extent. If he sees that the pool that holds his tadpoles is running out of water, he’ll use his back legs to dig a channel into a larger pool to both replenish the smaller pool and allow the tadpoles to escape. On the other hand, he’ll sometimes eat his young.
• African bullfrogs shed their skin in its entirety occasionally, splitting down the back first, then across their belly so the frog can pull its arms and legs out, then work the skin off its head. Rather than waste any food source, the frog then eats the old skin.
• After burrowing underground, some African bullfrogs keep only their noses above ground to better grab any unsuspecting prey.

Evolution and History

The African bullfrog has evolved several adaptations suited to its environment.

As the biggest threat to these frogs is habitat destruction, they have developed adaptations that allow them to thrive in a range of climates from hot deserts to velds (high open lands that reach below-freezing temperatures in the winter). One of the adaptations the frog has developed to stay alive in a hostile environment is that when it estivates (becomes dormant), it sloughs off its skin one layer at a time to form a cocoon around itself for protection and to reduce evaporative water loss from its body. While cocooned, the frog decreases its metabolic rate. All of this allows the bullfrog to withstand the African dry season, which can last 7 to 8 months.

Another adaptation is its odontodes—tooth-like projections on its jaw used to grab prey and fight off predators. While many frogs have “pedicel” teeth divided into three sections, African bullfrogs have non-pedicellate teeth composed of dentin with an enamel-tipped crown.

Classification and Scientific Name

The African bullfrog’s scientific name is Pyxicephalus adspersus. It is a member of the Pyxicephalidae family of sub-Saharan frogs and belongs to the Pyxicephalus genus, which comes from the Greek for “round box head.”

The African bullfrog is the largest of the species that belong to Pyxicephalus, which includes the edible bullfrog (Pyxicephalus edulis), Calabresi’s bullfrog (Pyxicephalus obbianus), and Pyxicephalus angusticeps, among others.

Appearance and Behavior

Male African bullfrogs grow up to about 9.6 inches long, while females are about half that size. The males of this big frog can weigh up to 3 pounds, and the females weigh about half that. This is unusual because in most frog species the females are bigger than the males.

A fully grown male African bullfrog is olive green, has a throat in shades of yellow or orange, and can be as big as a dinner plate. The female is much smaller and olive green to light brown with a white or cream throat. Younger bullfrogs are more brightly colored, with mottled skin and white or yellow lines that run down their back. The colors fade to the adult coloring as the frog gets older, though some females do retain the lines. Adult frogs have a knob on their hind foot shaped like a shovel that helps them dig. Their back toes have some webbing while the stubby front toes do not.

The African bullfrog has a similar body to most other frogs. Its powerful legs help it jump away from predators and threats, and its skin protects its internal organs, helps it take in oxygen, and absorbs water. The skin is also full of glands. Many of these glands are located on the back and head and secrete a solution that keeps the skin moist and protects it against pathogens. Its slickness also helps the frog escape predators.

The African bullfrog is noted for having a huge skull and robust skeleton, and Though they do not have true teeth, their bottom jaw has three tooth-like growths on the skin surface called odontodes, which are used to grab and hold prey. The African bullfrog is one of the few frog species to have such ‘teeth.’

African bullfrogs are solitary except during the breeding season, which occurs after heavy rains that allow shallow, temporary pools of water to form. A group of frogs is generally called an army or a knot.

Habitat

The bullfrog can be found in a wide variety of habitats in sub-Saharan Africa. It’s found as far east as Somalia, as far west as Nigeria, and south into South Africa.

Though they are amphibians, African bullfrogs can live in climates that stay dry for years. They can live in the mountains but are probably happiest near bodies of water. The secret to their adaptability is that they dig chambers in the soil when the climate becomes too harsh, enter the chambers, and become dormant until conditions are more favorable.

Diet

Like most other frogs, the African bullfrog is a carnivore and eats reptiles including snakes, amphibians, insects, mice and other small mammals, plus small birds. They will eat their own species, and it is rather common for a bullfrog tadpole to begin to eat its brothers and sisters when it emerges from its egg as a tadpole. A father will sometimes make a meal of some of the eggs or tadpoles he is guarding.

It hunts by extending its sticky tongue, which attaches to prey and draws it into the frog’s mouth, where it can be held by the dermal teeth while the frog kills it.

A person who keeps the African bullfrog as a pet needs to make sure that it does not try to eat anything that is indigestible, such as toys or other foreign objects. the frog should not be fed muscle meat such as ground beef, as it does not supply the nutrients the animal needs. Frogs can be subject to infections in their skin and eyes and ammonia poisoning if their enclosure’s maintenance is neglected.

Predators and Threats

Natural predators include birds of prey that are big enough to grab the frogs with their talons or beaks, and monitor lizards and turtles that attack young frogs and then swallow them.

People who share habitats with African bullfrogs sometimes eat them, considering the meat a delicacy.

Reproduction, Babies, and Lifespan

The African bullfrog is sexually mature when it’s about 1.5 to 2 years old. During the breeding season, the younger males gather in one small area of the pool while the bigger males go to the center and try to chase each other off. They will sometimes fight to the death to do this. They emit a sound resembling a loud “whoop!” to attract females. The females enter the water and attempt to mate with the dominant male. A female African bullfrog releases up to 4,000 eggs in the breeding pool. Then, she leaves to let the father guard them.

There is no gestation period for the African bullfrog. Once she is clasped by the male she has selected, the female lays eggs on the surface of the water, and the male fertilizes them. The tadpoles hatch about two days later. The young of bullfrogs are called larvae, tadpoles, or polliwogs.

Since African bullfrogs are amphibians, their young do not nurse and therefore do not need to be weaned. They are omnivorous and will consume vegetation, live and dead insects, fish that are small enough to handle, and other tadpoles. As they mature, they turn into exclusive carnivores.

Tadpoles grow into young frogs in about three weeks. If it survives infancy, the African bullfrog typically lives around 20 years in the wild and has been known to live as long as 45 years in captivity. As they age, they may, like other amphibians, be subject to diseases such as chytridiomycosis, which attacks the skin, and other diseases caused by ranaviruses.

Population

Though the exact population of African bullfrogs is unknown, their conservation status is “Least Concern,” although it’s believed their population is declining.