Like the caterpillar that becomes a butterfly, the tadpole (sometimes called a polliwog) also undergoes a metamorphosis. After hatching in the water, the aquatic tadpole transforms into an air-breathing frog.
Frogs lay eggs in groups called clutches. Within one hour of being laid, each fertilised egg begins to divide and form into a tadpole.
When the tadpole has external gills and a mouth, it is ready to hatch. For the first few days after hatching, most tadpoles stay hidden as their gills and muscular system mature.
A tadpole has a chubby body and a long, flat tail, bearing little resemblance to the frog it will soon become. Like a fish, it breathes through its gills and swims freely.
Inside the tadpole's mouth are toothlike rasps, which it uses to scrape algae from the underside of plants and rocks.
As the tadpole matures, the gills begin to recede into its body. First legs, then arms develop; the tail shrinks. The tadpole begins to feed on dead insects in addition to plants.
As soon as its lungs become fully developed, the new froglet can leave the water and live on land. It may still have a tail stub, which soon disappears, according to science writer Mark W. Moffett. The entire transformation from a tadpole into a frog takes approximately 12 to 16 weeks.