Say you are thirsty. Can you put your hand in a glass of water and drink it through your skin? Of course you can’t! But some animals can absorb water this way. These animals are called amphibians.
Amphibians are very interesting creatures. They
live a kind of double life. They spend the first part of their life in water
and the second part on land. In fact, the word amphibian comes from two
Greek words that mean “both” and “lives.”
KINDS OF AMPHIBIANS
An amphibian is an animal that has moist,
hairless skin. Amphibians are cold-blooded, which means they cannot make their
own body heat. They get warm in the sun and cool off in the shade. The three
main groups of amphibians are frogs and toads, salamanders, and caecilians. All
amphibians have backbones.
The three kinds of amphibians look very
different from each other. Frogs and toads have legs but do not have tails.
Salamanders have short legs and long bodies ending in tails. Caecilians do not
have any legs. They look a lot like big earthworms.
There are more than 4,000 different species
(kinds) of amphibians in the world. Nearly all amphibian species are frogs
or toads. Toads differ from frogs in the roughness of their skin. Toads have
bumpy skin, and frogs have smooth skin. Toads also have shorter legs than
frogs.
The biggest amphibian found on Earth is the Japanese
giant salamander. It can grow to be longer than 5 feet (1.5 meters). Tiny
frogs, such as the gold frog, are only about 0.4 inch (about 1 centimeter)
long.
THE DOUBLE LIFE
Most amphibians start out as larvae. Larvae look totally
different from adult amphibians. Frog and toad larvae are sometimes called
pollywogs or tadpoles. These larvae look more like fish. They live underwater
and have a tail that they use for swimming. They breathe through gills to get
oxygen from the water.
An amphibian’s body changes completely when it goes
from a larva to a grown-up. This kind of change is called metamorphosis. Most
grown-up amphibians have lungs for breathing instead of gills. Some have both
lungs and gills.
Full-grown amphibians have legs for moving about on land.
Frogs and toads have strong hind (back) legs for jumping. Most salamanders have
four short legs and a long, strong tail. The tail helps them keep their balance
while walking and pushes them forward while swimming. Caecilians never grow
legs. They use their hard heads as battering rams when they burrow in the soil.
In water, they swim as eels do, by wiggling their wormlike bodies back and
forth.
AMAZING SKIN
Amphibians can “drink” through their skin. The skin of
an adult amphibian is able to absorb water from its surroundings. Most
amphibians do not even swallow water. Their skin soaks up as much as they need.
Amphibians also breathe through their skin. Their skin
takes in oxygen as well as water. Most grown-up amphibians get oxygen through
both their lungs and their skin. But some salamanders get all their oxygen
through their skin. They do not even have lungs or gills.
Slimy stuff called mucus covers an amphibian’s
skin. The mucus keeps just the right amount of salt and water in the amphibian.
In some species the mucus is poisonous, which helps keep predators from eating
the amphibian.
SENSING THE WORLD
Some amphibians have good eyesight and hearing, and
some do not. Most frogs and toads can hear well. Salamanders, caecilians, and
some frogs can only sense vibrations in the ground or water.
Frogs have great eyesight. They see through two
bulging eyes that stick out from their heads. Most caecilians are totally
blind.
All amphibians can smell and taste pretty well.
Caecilians use feelers on their heads. Amphibians have a place in their mouths
called Jacobson’s organ that helps them smell and taste the world around them.
AN AMPHIBIAN’S LIFE
Amphibians that live in cold places spend most of
their time trying to keep wet and warm. In hot places, they try to keep wet and
cool and usually come out only at night. During the day, they stay under rocks
or logs or in the ground.
Amphibians hibernate (become inactive) during
cold winters. They become inactive in hot places during the summer.
Almost all grown-up amphibians are meat eaters.
Frogs and salamanders have sticky tongues. They flick out their tongues to
catch insects, spiders, and other animals. Caecilians have sharp teeth for
grabbing their prey.
Amphibians mate when it is rainy outside. They
gather in groups to find mates. Some male salamanders show bright colors to get
the attention of females. Male frogs call out to females. Their call sounds
like this: “ribbet.” Female amphibians lay eggs in water or wet places on land.
Larvae hatch out of the eggs.
No one knows how long amphibians live in the
wild. Some captured toads have lived 30 years.
WHERE AMPHIBIANS LIVE
Amphibians live everywhere except Antarctica. They can
be found in grasslands, rain forests, evergreen forests, deserts, and mountain
areas. Caecilians live only in the tropics.
Amphibians need water to breed and have babies. So most
of them live near ponds, swamps, or streams. A few species can even find water
in deserts. Some burrowing frogs live in a dry part of Australia called the
outback. They breed and feed only when it rains, which is not very often.
DISAPPEARING AMPHIBIANS
Amphibians have lived on Earth for more than 300 million
years. But recently, something scary has been happening to them. Amphibians are
disappearing. There are fewer and fewer amphibians in many parts of the world,
including North America, South America, and Australia. No one knows why.
Some amphibians have also been found with extra
legs or other strange problems. Scientists are working hard to find out what is
happening to the amphibians.