What Do Bullfrogs Eat? Insects, Fish, Snakes and Birds

What adult bullfrogs eat

The American bullfrog has one of the broadest diets of any frog in North America. Studies of stomach contents across its range have found a long and sometimes surprising list of prey:

• Invertebrates: beetles (including water beetles), dragonflies and their larvae, grasshoppers, bugs, spiders, snails, earthworms and leeches.
• Crustaceans: crayfish are a major food in many ponds and streams.
• Fish and amphibians: small fish, fish eggs, tadpoles, newts and salamanders, and frogs of many species, including smaller bullfrogs.
• Reptiles: small snakes such as garter snakes and water snakes, young turtles and small lizards.
• Birds and mammals: occasionally ducklings, songbirds, mice, voles, shrews and even bats.

Insects and other invertebrates are eaten most often, but vertebrates can make up a large share of the total food by weight, especially for big adults. That high proportion of vertebrate and aquatic prey is unusual among North American true frogs.

How bullfrogs hunt

Bullfrogs are sit-and-wait (ambush) hunters. A frog sits motionless at the water’s edge, on a lily pad or floating among plants with only its eyes showing, and waits for something to move. Movement is the trigger: bullfrogs react mainly to prey that wriggles, swims, flies or walks past.

When prey comes close, the frog turns to face it, may hop closer, then makes a fast lunge with its mouth opening. The sticky tongue shoots out to hit the prey while the wide jaws close around it. Large prey that does not fit in at once is pushed in with the front feet. Bullfrogs can also catch prey underwater and are able to aim correctly despite light bending at the water’s surface.

Because they rely on movement, bullfrogs rarely notice food that lies completely still, and they generally ignore dead prey. Hunting happens both by day and at night, but warm, humid evenings are especially busy, when insects swarm near the water and many small animals come down to drink or cross the shore.

Frogs do not chew. A bullfrog has only tiny teeth in the upper jaw for gripping, and it swallows its catch whole. It even uses its eyes to help: the eyeballs sink into the head, pressing down on the roof of the mouth and helping push food toward the throat. Read more in Do frogs have teeth?

Bigger frogs, bigger prey

What a bullfrog eats depends strongly on its size. Young frogs just out of the water feed mostly on small insects and other invertebrates. As they grow, they take larger prey, and the biggest adults are the ones that eat crayfish, frogs, snakes, birds and rodents. In general, a bullfrog will try to swallow almost anything that moves and fits in its very wide mouth.

Diet also changes with place and season. In one pond crayfish may dominate, in another dragonflies or small fish. In the breeding season, when many frogs gather, cannibalism of young bullfrogs can be common.

What bullfrog tadpoles eat

Bullfrog tadpoles live very differently from the adults. They have small mouths with rows of tiny horny “teeth” (not true teeth) and a beak for scraping. They feed mostly on:

• algae growing on rocks, plants and the pond bottom,
• tiny floating particles such as bacteria, pollen and single-celled organisms, trapped on mucus in the throat,
• soft plant material and, occasionally, dead animals or eggs.

Because the tadpole stage can last one to three years in cooler areas, these grazers grow very large before turning into frogs.

Why the bullfrog’s appetite matters

In its native range in eastern North America, the bullfrog is one part of a balanced food web: it eats many animals, and in turn is eaten by herons, otters, raccoons, snakes, turtles and alligators.

Where people have introduced it, the same appetite becomes a problem. In California, bullfrogs prey on the threatened California red-legged frog and on young giant garter snakes and western pond turtles. In Europe they eat native frogs, newts and other pond life. Adult bullfrogs also eat many of the insects and other animals that would normally prey on young bullfrogs, such as dragonfly larvae and water bugs. This helps bullfrogs take over ponds outside their native range, as explained in Are bullfrogs invasive?

Myths and facts about bullfrog food

Myth: Frogs only eat flies. Small frogs eat mostly insects, but a big bullfrog is a true generalist predator that also eats vertebrates.

Myth: Bullfrogs are immune to anything they eat. Bullfrogs do tolerate stinging wasps and spiny fish surprisingly well, and some evidence suggests partial resistance to the venom of copperheads and cottonmouths. They are not invulnerable, though; larger venomous snakes also eat bullfrogs.

Fact: Bullfrogs eat other frogs regularly. Frogs, including other bullfrogs, are among the most common vertebrate prey in many studies.