The Life Cycle of a Frog

It includes three stages: egg, larva, and adult

Southern tree frogs mating on black background
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The life cycle of a frog consists of three stages: egg, larva, and adult. As the frog grows, it moves through these stages in a process known as metamorphosis. Frogs are not the only animals to undergo metamorphosis; most other amphibians also undergo remarkable changes throughout their life cycles, as do many species of invertebrates. During metamorphosis, two hormones, prolactin and thyroxine, control the transformation from egg to larva to adult.

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Breeding

Close-Up Of Frogs Mating On Banana Leaf

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The breeding season for frogs usually occurs during the spring in temperate climates and during the rainy season in tropical climates. When male frogs are ready to breed, they often use loud croaking calls to attract partners. Males produce these calls by filling a vocal sac with air and moving the air back and forth to create a chirp-like sound.

When mating, the male frog holds onto the female's back, clasping his front legs around her waist or neck. This embrace is referred to as amplexus; its purpose is to ensure that the male is in the optimal position to fertilize the female's eggs as she lays them.

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Stage 1: Egg

Frog surrounded by eggs

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Many species lay their eggs in calm water among vegetation, where the eggs can develop in relative safety. The female frog lays numerous eggs in masses that tend to clump together in groupings known as spawn. As she deposits the eggs, the male releases sperm onto the eggs and fertilizes them.

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 begins to take the form of a tadpole, the larva of a frog. Within one to three weeks, the egg is ready to hatch, and a tiny tadpole breaks free.

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Stage 2: Tadpole (Larva)

Tadpoles

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Tadpoles, frogs' larvae, 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. After absorbing the yolk, the tadpole is strong enough to swim on its own.

Most tadpoles 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 hind limbs. Its body elongates and its diet grows more robust, shifting to larger plant matter and even insects. Later in development, front limbs grow and tails shrink. Skin forms over the gills.

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Stage 3: Adult

Tree frog

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At approximately 12 weeks of age, the tadpole's gills and tail have been fully absorbed into the body, meaning that the frog has reached the adult stage of its life cycle. It is now ready to venture out onto dry land and, in time, repeat the life cycle.