Life Cycle of a Frog
Stage 1: Egg
Many species lay their eggs in calm water amongst vegetation where the eggs can develop in relative safety. The female frog lays numerous eggs in masses that tend to clump together (these egg masses are referred to as spawn). As she deposits the eggs, the male releases sperm onto the egg masses and fertilizes the eggs.
In many species of frogs, the adults leave the eggs to develop without further care. But in a few species, parents remain with the eggs to look after them as they develop. As the fertilized eggs mature, the yolk in each egg splits into more and more cells and it begins to take on the form of a tadpole. Within one to three weeks, the egg is ready to hatch, and a tiny tadpole breaks free of the egg.
Stage 2: Tadpole (Larva)
A frog's larva is also called a tadpole. Tadpoles have rudimentary gills, a mouth, and a long tail. For the first week or two after the tadpole hatches, it moves very little. During this time, the tadpole absorbs the remaining yolk left over from the egg, which provides much needed nourishment. At this stage, tadpoles have rudimentary gills, a mouth and a tail. After absorbing the remaining yolk, the tadpole is strong enough to swim on its own.
Most tadpoles are feed on algae and other vegetation so they are considered herbivores. They filter material from the water as they swim or tear away bits of plant material. As the tadpole continues to grow, it begins to develop hindlimbs. Its body elongates and its diet grows more robust, shifting to larger plant matter and even insects. Later in their development, front limbs grow and their tail shrinks. Skin forms over the gills.
Stage 3: Tadpole with Legs
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.
Stage 4: Froglet
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.
Stage 5: Adult
At approximately 12 weeks of age, the tadpole's gills and tail have been fully absorbed into the body—the frog has reached the adult stage of its life cycle and is now ready to venture out onto dry land and in time repeat the life cycle.