Frogs and toads call out loudly when it is time to find a mate, and the males do it by breathing in air with their lungs and then bouncing the air between their vocal sacs and their lungs. Frogs make their calls with the help of one or two pouches of skin called vocal sacs, which work like echo chambers to amplify the sound of a call. A male bullfrog's low call can be heard for more than a kilometer, and male bullfrogs croak both to attract mates and to claim their territory. Explosive breeders gather in large numbers and call for mates for only a few days, using temporary wetlands because there are no fish there to eat their eggs. A male will often stop calling for short periods to pick off a receptive female hopping towards a call.

What happens to a call after it leaves the pond? A frog's ears, called tympanum, look like flat circles behind the eyes, and the size of the tympanum and the distance between them determine which sounds a frog hears best, so its ears are tuned to its own species' calls. This helps a female find males of her species in a noisy pond. In male bullfrogs, the tympanum, the round circle on the side of the head near the eye, is much larger than the eye. During breeding, female frogs and toads listen carefully and hop closer to males with a deeper or more powerful call, which signals a larger size and a greater ability to survive and reproduce, and larger, more aggressive animals are also better at defending territories where eggs are present.

In a study of how frogs catch insects, a frog's tongue captured an insect in under 0.07 seconds, which was five times faster than a human eye blink. A frog cannot see while its tongue is striking, so it can only make a catch by taking careful aim in advance. A frog's saliva is viscoelastic, which means it has properties of both a fluid and a solid. In a study of frog tongues, low-viscosity (runny) saliva helped the tongue hit and release prey, while high-viscosity (thick) saliva helped it hold on to prey. Frogs cannot chew, so prey is swallowed whole; any teeth are on the upper jaw and only hold prey. Frogs need good eyesight to catch fast insects, and their large eyes see a wide range of colors and see well in dim light. A frog's eyes also help it swallow: as the frog swallows its prey, the eyes sink through openings in the skull and help force the food down the throat, which is why frogs seem to blink as they eat.

A tadpole is a young frog that lives in water and breathes with gills, and the change from a tadpole into a frog is called metamorphosis. During metamorphosis the hind legs emerge first, then the front legs, the gills are replaced by lungs, and the digestive system typically shifts from plant-based to carnivorous. The tail is gradually reabsorbed as a source of energy, and the young frog ventures onto land with a tail stub. Metamorphosis usually takes several weeks. Species that breed in temporary ponds may develop more quickly, because if the pond dries up too soon the underdeveloped tadpoles will perish. By contrast, bullfrog tadpoles may take several years to grow into frogs, and a bullfrog tadpole can take two winters, or almost three years, to turn into a frog.

The gastric brooding frog of Australia swallows her fertilized eggs, and the tadpoles stay in her stomach for up to 8 weeks until hopping out of her mouth as little frogs. Among Darwin frogs, the male stores the tadpoles in his vocal sac. A few frogs give birth to live young: members of the African genus Nectophrynoides keep their eggs inside the mother, and some nourish the young as they grow, so the young are born as miniatures of the adult. A strawberry poison dart frog lays eggs on land, not in a pond, and when the tadpoles are ready to hatch, the mother carries them on her back to water-filled bromeliads in the trees, where she feeds them unfertilized eggs. Baby Surinam toads grow up on their mother's back and do not swim around as tadpoles.

Frogs have more than one answer to a hard season: in dry regions, frogs may bury themselves underground or cut back on breathing through the skin, which also reduces water loss. Wood frogs spend the winter frozen and thaw out when the weather warms. When blood freezes in most animals, nothing delivers oxygen and nutrients to the organs, so extreme metabolic damage occurs. At the start of a wood frog's winter freeze, its liver makes large amounts of glucose that flush into every cell in its body. A frozen wood frog thaws from the inside outward. Wood frogs and spring peepers can freeze completely in winter, so they can start breeding much earlier than other amphibians. As of November 2026, scientists do not yet understand what starts a wood frog's heart again after it has been frozen for the winter.

Bright colors on tropical frogs warn predators that they are poisonous, but frogs are not above bluffing: some nonpoisonous species have adopted the colors of poison dart frogs to trick predators into giving them a wide berth they do not deserve. Certain frogs of Central and South America have especially strong poisons in their skin, and there are about 170 kinds of poison dart frogs. In the wild, they are too toxic to touch. Golden poison frogs do not act aggressively toward people; the danger lies in their very toxic skin. Captive ones tend to lose their toxicity without the wild prey that are the source of the toxin, and the Panamanian golden frog gets its toxins from the insects it eats in the wild. Many dull-looking frogs also have hidden flash colors, bright patches on the belly, groin or backs of the thighs.

A toad's skin has glands that make a poison, which helps protect the toad from predators. A toad's skin is bumpy, a bit like warts, and the large glands behind the eyes are called parotoid glands. The poison is called bufotoxin, and it can kill small animals and cause allergic reactions in people. Because a toad's poison can irritate the mouths of animals that bite it and the skin of people, nobody should lick or eat a toad, and it is best not to handle one. A toad may puff up its body to look bigger and inedible when a predator is near, and its bumpy skin helps it blend into its surroundings. You may have heard that touching a toad gives you warts, but in fact, touching a toad does not give you warts.

The disease called chytridiomycosis is caused by the chytrid fungus Batrachochytrium dendrobatidis. As of November 2026, AmphibiaWeb says the fungus is associated with the global loss of hundreds of amphibian species, a spectacular loss of biodiversity that some say is the worst in recorded history. As of November 2026, habitat loss and invasive species are also among the biggest threats to frogs and toads, and bullfrogs that people have introduced may be driving native frogs to extinction in some areas. As of November 2026, a 2004 global assessment found that nearly one-third of the world's amphibians are threatened, representing 1,856 species, and most scientists agree that there is a worldwide decline in frog numbers. Amphibians react strongly to changes in their surroundings, so scientists use them as signs of how healthy a place is.

Words to know

• tympanum: frog ear
• metamorphosis: tadpole becoming frog
• viscoelastic: fluid and solid
• chytridiomycosis: chytrid fungus disease