means "having a double life."
.Most frogs hatch from eggs as tadpoles or pollywogs. Living
in fresh water, they resemble fish, breathe through gills, and
generally eat plant material. Gradually, they grow four legs and
develop lungs that can breathe air. Their eyes move from the
sides of the head to the top. The tail shrinks until it disappears.
After this change, or metamorphosis, most adult frogs live
on land. Instead of eating plants, they catch insects, worms,
and other animals with their long tongues. At mating time,
they return to the water to lay eggs.
The double lives of frogs and other amphibians let them
evolve to become the first vertebrates - animals with
backbones - to live on land. While ancient frog fossils are
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Frogs are incredibly diverse. "Every time we take a trip somewhere
we find yet more new species," says Joseph Mendelson of Zoo
Atlanta, who has discovered dozens of species.
So, yes, most frogs start out in water and then live on land.
But many species spend their whole lives in water. Some frogs
live only on land. And a few live entirely underground. Some
species even skip metamorphosisaltogether.
Frogs function in unexpected ways, too. While adult frogs
have lungs (except, at least one species doesn't), frogs generally
absorb most of their oxygen through the skin, especially skin
inside the mouth. Lungs help for energy-intensive activities,
like jumping or mating.
Frogs also absorb water through the skin. "Frogs have a
drink patch on their lower bellies," says Diane Barber at Texas's
Fort Worth Zoo.
Plus, frogs are the only creatures in the world that swallow
with help from their eyeballs. Push against your cheek with
a finger. When frogs close their eyes while swallowing, their
eyeballs bulge into their mouths in a similar way. This helps
force food down the throat.
SurvivaL Strategies
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Frogs live on every continent except Antarctica. Different
species thrive in wetlands, deserts, forests, and other habitats.
e "They're just extremely adaptable creatures,'' says Barber.
Camouflage protects many frogs by letting them blend
, into the background. Bright colors warn potential predators
that other species are poisonous. Still other species use
mimicry - they're brightly colored like some toxic frogs, but
not poisonous at all.
Frog calls help species survive by attracting mates. Male frogs
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