Amphibians
Argentine Horned Frog
Ceratophrys ornata · also called pacman frog, ornate horned frog, escuerzo
The Argentine horned frog is a frog that is mostly mouth. Round, squat, and gaudily patterned, it sits half-buried in the grassland of southern South America waiting for a meal to walk past, and it will attack almost anything — a beetle, a mouse, a snake, or another frog nearly its own size.
Overview
Argentine horned frogs live in the pampas — the humid grasslands and seasonal wetlands of northeastern Argentina, Uruguay, and southern Brazil. It is a sit-and-wait ambush predator, spending most of its time dug into soft soil or leaf litter with only its eyes and the top of its enormous mouth exposed. It is largely nocturnal and crepuscular in the warm, wet season and dormant underground the rest of the year.
An eating machine
The horned frog’s body plan is dominated by its gape. The mouth is nearly as wide as the frog is long, the head is broad and heavily built, and the lower jaw carries bony ridges and small fang-like odontoids. When prey comes within reach, the frog explodes forward, engulfs it, and clamps down, using its front legs to shove larger animals down its throat. Its bite force, relative to size, is among the strongest measured in any amphibian.
The horns are soft, pointed flaps of skin above the eyes; they are not weapons but camouflage, disrupting the outline of the head so the buried frog looks like a clump of dead leaves.
Surviving the dry season
When the grasslands bake and the pools vanish, the horned frog aestivates. It digs in and sheds layer after layer of skin that dries into a tough, papery cocoon, sealing in moisture. It can remain like this for months, its heart and breathing barely ticking over, until the rains return and it bursts out to feed and spawn in the flooded ground.
Reproduction
Breeding is triggered by heavy rain filling temporary ponds. Males call from the water, females lay clumps of eggs, and the tadpoles — which are, predictably, highly carnivorous, eating other tadpoles and small pond animals — develop fast to beat the drying of the pool.
Status
The Argentine horned frog is listed as Near Threatened and is declining. Its pampas habitat has been extensively converted to soy and cattle farming, and it is also collected from the wild for the international pet trade, where “pacman frogs” are popular. Captive breeding is well established and now supplies most of that demand, but the species’ small range and specific grassland-and-wetland needs leave it vulnerable.
Argentine Horned Frog: common questions
Why is it called a pacman frog?
For its shape and behaviour. The Argentine horned frog is almost circular when viewed from above and consists mostly of a huge, wide mouth, so it looks like the video-game character Pac-Man, and it feeds the same way — sitting still and engulfing anything edible that comes close. "Pacman frog" is the pet-trade name for Ceratophrys species in general; this one and the Cranwell's horned frog are the two most commonly kept.
How hard can a horned frog bite?
Hard for a frog. Adult Ceratophrys ornata bite with around 30 newtons of force, and researchers estimate that the largest horned frogs and their giant fossil relatives could have exceeded 500 newtons — comparable to a medium-sized mammalian carnivore. They have bony ridges and small tooth-like projections ("odontoids") on the lower jaw, and a determined frog can draw blood from a finger and is reluctant to let go.
What does a horned frog eat?
Almost anything it can cram down. Its diet in the wild includes large insects, spiders, other frogs, lizards, small snakes, and rodents, and captive frogs will attempt prey as big as themselves, sometimes choking or being injured in the process. The hunting method is pure ambush — the frog digs itself into soft ground until only its eyes and mouth are exposed, waits, and then lunges and clamps down, walking larger prey into its throat with its front feet.
How does the frog survive the dry season?
It aestivates. When the pampas dries out, the horned frog burrows down and sheds successive layers of skin that harden into a nearly watertight cocoon around its body, leaving only the nostrils clear. Sealed inside, its metabolism drops and it can wait out months of drought. When heavy rain soaks the ground, the frog rehydrates, breaks out, and emerges to feed and breed in the temporary pools.