By between 12 to 16 weeks, depending on water and food supply, the frog has completed the full growth cycle. Some frogs that live in higher altitudes or in colder places might take a whole winter to go through the tadpole stage...others may have unique development stages that vary from your "traditional" tadpole-in-the-water type.
Frogs lay their eggs in water or wet places. A floating clump of eggs is called frog spawn.
The large and slippery mass of eggs are too big to be eaten. This is nature's way of protecting them. But, the smaller clumps of eggs will be eaten by the creatures living near or in the pond.
The egg begins as a single cell. Several thousand are sometimes laid at once. It becomes surrounded by a jellylike covering, which protects the egg. The female may or may not stay with the eggs to take care of the young after she has laid them. The egg slowly develops. But, only a few develop into adults. Ducks, fish, insects, and other water creatures eat the eggs.
The Cell Splits
The single cell in the egg eventually splits into two. These two split making four cells, and so on. Eventually, there are many cells in the egg.
The mass of cells in the egg come to form an embryo. Organs and gills begin to form, and in the meantime, the embryo lives off of its internal yolk. This supplies it with nutrients for 21 days. Then . . .
After its 21 day development period, the embryo leaves its jelly shell, and attaches itself to a weed in the water. This quickly becomes a tadpole, a baby frog. The tadpoles grow until they are big enough to break free into the water. This can take from 3 days to 3 weeks, depending on what kind of frog they will become. They eat very small plants that stick to larger plants in the water. These tiny plants are called algae. The tadpole has a long tail, and lives in the water. It is extremely vulnerable, and must rely on its camouflage to protect it.
The tadpole has a long tail, and lives in the water. It is extremely vulnerable, and must rely on its camouflage to protect it. The tadpoles also face danger by being eaten by other water animals. Sometimes the pond dries up. As a result the tadpoles die.
The Tadpole Begins To Change
After about five weeks, the tadpole begins to change. It starts to grow hind legs, which are soon followed with forelegs. Behind their heads bulges appear where their front legs are growing. Their tails become smaller. Lungs begin to develop, preparing the frog for its life on land. Now and then, they wiggle to the surface to breathe in air. The tail becomes larger and makes it now possible for the tadpole to swim around and catch food. They eat plants and decaying animal matter. Some tadpoles eat frogs eggs and other tadpoles.
Almost There . . .
Over time, the tadpole becomes even more froglike. They have shed their skin and lips. Its mouth widens, and it loses its horny jaws. The tail becomes much smaller, and the legs grow. The lungs are almost functioning at this point.
Eleven weeks after the egg was laid, a fully developed frog with lungs, legs, and no tail emerges from the water. This frog will live mostly on land, with occasional swims. The tiny frogs begin to eat insects and worms. Eventually, it will find a mate. The way this is done varies depending on the species. The female lays the eggs, the male fertilizes them, and the whole process begins again.