Frogs often produce large numbers of eggs—up to 10,000 or more—surrounded by a jellylike coating that protects the eggs from predators and keeps them from drying out. Those that provide some care for their young usually produce relatively few eggs. When these tadpoles hatch, they drop into the water below. Many species lay their eggs in water trapped in tree cavities or cup-shaped parts of plants. In warmer climates, eggs may hatch within 1 or 2 days, while in colder environments they may take 30 to 40 days to hatch.
Tadpoles, which usually live in water, look somewhat like small fish. A tadpole has an oval body, gills for breathing, and a long, muscular tail with fins along the upper and lower edges for swimming. Tadpoles have two small eyes, one on each side of the head. A tadpole's mouth has a horny beak and rows of tiny, comblike teeth that the animal uses to scrape algae from underwater plants and bite off bits of plant material. Typically, frogs spend a few months as tadpoles before metamorphosing into adults.
Metamorphosis involves extreme changes in both external and internal body parts. The tadpole grows legs—the hind legs appear first—and loses its tail. It loses its gills and grows lungs, and the structure of the heart, digestive system, and skeleton changes. The horny beak and other mouthparts adapted for eating algae disappear and are replaced by the long, sticky,tongue that helps adult frogs catch insects. Frogs reach reproductive age anywhere from several months to several years after metamorphosing. Most frogs probably live only a year or two in the wild.