Amphibians
Horned Frog
Ceratophryidae · also called Pacman frog, South American horned frog
A horned frog barely bothers to be a frog. It does not chase, it does not travel, and it can spend days without moving. It buries itself in the leaf litter until only its eyes and the little horns above them show, and then it waits — and when something the size of a mouse or another frog walks past, the whole front half of the animal turns out to be mouth.
Overview
Horned frogs are the family Ceratophryidae, around 12 species in South America east of the Andes. All are squat, wide-mouthed ambush predators of seasonally wet grassland and forest floor. The best-known are the Argentine and Cranwell’s horned frogs, sold worldwide in the pet trade as Pacman frogs. The “horns” are pointed flaps of the upper eyelid, thought to break up the frog’s outline among dead leaves.
Mostly mouth
A horned frog’s head can be over half its body width, and a large one will lunge at prey close to its own size — sometimes fatally, when the meal will neither go down nor come back up. The bite is powered by many small recurved teeth, tooth-like bumps on the palate, and eyeballs that retract into the mouth to help force food down. For its size, the bite is one of the hardest measured in any frog.
Waiting out the drought
When the breeding pools dry, a horned frog burrows down and wraps itself in a cocoon of shed skin that seals in water, then waits underground through months of dry season until heavy rain breaks it out to feed and breed. Its tadpoles are aggressively carnivorous from hatching and can call underwater.
Status
Horned frogs as a family are Not Evaluated. Several species remain widespread, but some have small ranges and are declining as the seasonally flooded grasslands they breed in are turned to farmland, with the chytrid fungus and pet-trade collection adding local pressure.
Horned Frog: common questions
Why is it called a Pacman frog?
The nickname comes from the animal's shape. A well-fed horned frog is almost circular seen from above, squat and flattened, with a mouth so wide it seems to split the body in half, which reminded hobbyists of the video-game character. It is used mainly for the two species most often kept as pets, the Argentine horned frog and Cranwell's horned frog, both bred in large numbers in captivity. The name is informal, but it has become so common in the pet trade that many keepers know the frogs only as Pacman frogs and are unaware they are South American ambush predators with a serious bite.
Do horned frogs really bite, and does it hurt?
Yes to both. Horned frogs are among the few frogs that will readily bite a person, lunging with a wide-open mouth at anything that looks like prey or a threat, including fingers. The jaws are lined with many small recurved teeth and the roof of the mouth carries bony, tooth-like odontoids, and the bite force is high for the animal's size, so a large individual can draw blood and hang on. It is not dangerous, but it is a genuine bite rather than a nip. Keepers are usually advised to feed with tongs and to expect the frog to treat a hand moving in the enclosure as something to attack.
How does a horned frog hunt?
By waiting. A horned frog shuffles backward into loose soil or leaf litter until only the top of its head and its eyes are exposed, and then stays motionless, sometimes for days, relying on its mottled skin and eyelid horns to blend into the ground. When an insect, frog, lizard, or small rodent comes within range, the frog explodes forward, engulfs the prey in its huge mouth, and clamps down, using the many teeth and the retracting eyeballs, which bulge down into the mouth cavity, to work the struggling animal down its throat. It is a pure sit-and-wait strategy that trades mobility for a very low energy cost between meals.
What happens to a horned frog in the dry season?
It goes underground and waits. Horned frogs live in places with a pronounced wet and dry season, and their breeding pools disappear for months at a time. As conditions dry, the frog digs down into the soil and enters a dormant state called estivation. It secretes mucus from its skin that dries into a tough, semi-transparent cocoon enclosing the whole body except the nostrils, which drastically slows water loss. In this sealed state its metabolism drops and it can survive for many months. The first heavy rains of the next wet season soak through, the frog breaks out, and it heads straight for the newly filled pools to feed and breed.