With few exceptions, frogs lay their eggs in water and spend the early part of their lives in water. In temperate zones, most frogs hibernate in mud. In spring or summer, the female lays thousands of tiny eggs in large masses. The eggs, fertilized by the male as they are discharged by the female, are held together by a jellylike substance that swells in water to form a protective coating.

During breeding season, when they want to find a mate, frogs often return to the place where they hatched. Usually, the males arrive first. Each male croaks loudly to establish its own territory. In many species, when the females arrive, the males puff up vocal sacs in their throats and make a special mating call. They wait for females to respond.After a female chooses a male, he climbs onto her back and holds onto her in the water. The female lays eggs and the male produces a milky substance that is poured over the eggs to fertilize (FURH tuhl lyz) them.

After a period of from several days to several weeks (varying with species, water temperature, and amount of sunshine) tadpoles hatch out. The tadpole, or polliwog, is a frog in the larval stage. It has a tail and breathes with gills. At first the tadpole is legless, but as it develops it acquires first hind legs and then front legs. The tail is gradually absorbed, lungs develop, and the animal is metamorphosed (changed) into an adult frog. An adult attains full growth in about three years and may have a life span of 10 years or more.

A tadpole doesn’t look much like a frog—but when it grows up, that’s exactly what it will be. Most types of frogs spend the first stage of life as tadpoles, which is simply another name for frog larvae.

Tadpoles hatch out of eggs that are covered by a thick, jellylike coat that keeps them moist. At first, tadpoles look a lot like fish. They have gills, lidless eyes, and finlike tails for swimming.

Some kinds of tadpoles go through metamorphosis in about 10 days. Others take as long as two years to change form completely.

During metamorphosis, a tadpole first grows hind legs. Then forelegs appear from under the gills. The mouth widens and a tongue develops. Then the lungs develop and the gills disappear. The skin gets thicker and tougher, nostrils form, and the body absorbs the tail: it disappears! The tadpole has become a frog.

Some frogs do not lay eggs in water. A frog found in the Solomon Islands lays large, tough-shelled eggs from which fully formed froglets are hatched. In some species of tree frogs, the female lays the eggs on leaves or carries them in a pouch on her back where they eventually hatch.

Tadpoles feed mainly on algae. After metamorphosis, the digestive system changes, and the frog eats flies, worms, slugs, spiders, caterpillars, and small beetles. The bullfrog is large enough to swallow crayfish and small birds. Some kinds of tropical frogs eat rats, bats, and snakes.

Most frogs have long, sticky tongues that can be rapidly extended to catch prey, which is swallowed whole. The teeth, located in the upper jaw and roof of the mouth, grasp the prey until it is swallowed.

Frogs in the wild will eat almost anything they can catch—but only if it’s still alive. Most frogs eat insects, snails, and tadpoles. Large frogs will also eat small mammals, birds, fish, and reptiles.Most frogs have a keen ability to spot movement. Once a frog recognizes a moving object as prey, it tries to catch it. Some frogs can flick their tongues out in a fraction of a second to grab their food. Other frogs use their jaws to trap their prey.

In the water, a frog may simply open its mouth and gulp its prey. Like most other amphibians, frogs have teeth. But they only use them to grip food, not to chew it. If a frog catches something that tastes bad, it spits it out. But if the frog likes its catch, it swallows it whole.