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Two lives, one animal

Why Do Frogs Start as Tadpoles?

A tadpole is built for water and a frog for land, so the animal rebuilds halfway through.

Tadpole Gills, tail, eats algaeFrog Lungs, legs, eatsinsects
Same animal, completely different equipment.

  1. Step 1 of 5

    Eggs must be laid in water.

    Bird egg Hard shell — safe inairFrog egg Jelly only — must staywet

    Frog eggs have no shell — only jelly — so they dry out in air. Water is not a preference, it is a requirement.

  2. Step 2 of 5

    A tadpole is a water animal.

    Gills for waterTail for swimmingLong gut for plant food

    It has gills for underwater breathing, a tail for swimming, and a long gut suited to grinding through algae.

  3. Step 3 of 5

    Then the body is rebuilt.

    1 Back legsappear2 Front legs,lungs develop3 Tail absorbed,not dropped

    Legs grow, lungs develop, the gut shortens for a meat diet, and the tail is absorbed for its nutrients rather than being shed.

  4. Step 4 of 5

    Two lives means two food supplies.

    Tadpole eats Algae in the pondAdult eats Insects on land

    Tadpoles eat algae; adults eat insects. Young and adults never compete for the same food, which lets far more of them survive.

  5. Step 5 of 5

    Adults still need damp skin.

    Damp frog skin Oxygen absorbeddirectly

    Frogs absorb a good share of their oxygen through their skin, which only works while wet. That is why they stay near water for life.

    Some frogs skip the tadpole stage entirely, laying eggs that hatch as tiny fully formed frogs.

The short version

Frogs live two lives — a gilled water tadpole and a lunged land adult — so young and adults never compete.

Try it yourself

Watch a pond through spring. Back legs appear first, then front legs, then the tail shrinks over a few days.

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