Sloths move slowly. People sometimes say sloths are slow because they are lazy, but that is not the reason. Sloths are slow because their leaf diet gives them little energy and their bodies use energy very slowly. A sloth uses energy about 40 to 45 percent as fast as expected for a mammal of its size. Sloths live in trees, high up in the rainforest canopy, in the tropical forests of Central and South America.

Sloths mostly eat leaves. Leaves give sloths very little energy, so sloths get few calories from their food. A sloth's stomach has four chambers full of bacteria that help break down the tough leaves. A single leaf can take about a month to travel through a sloth's body.

A sloth's body works in some surprising ways. Its body temperature rises and falls with the temperature around it. Sloths cannot shiver to warm up, because they have so little muscle. Sloths warm up by moving into the sun and cool off by moving into the shade. Three-toed sloths can turn their heads about 270 degrees, almost all the way around.

Moving slowly helps sloths go unnoticed by hunters that find prey by sight. Sloths are hunted by big birds and big cats, such as harpy eagles, jaguars and ocelots. A curled-up sloth can look like a termite nest or a knot in the wood. Sloth hairs have grooves or cracks where algae can take hold and grow. The green algae help a sloth blend in with the green leaves. A sloth's fur is also home to moths, beetles and other tiny animals.

About once a week, a sloth climbs down from its tree to go to the bathroom. When it does, it can pass up to about one-third of its body weight. Sloths live alone, except for a mother with her baby or sloths that are mating. A mother sloth has one baby at a time. The baby crawls onto its mother's belly right after it is born and clings to her. It learns which leaves are safe to eat by tasting leaves from her mouth.

There are two kinds of sloth: two-toed sloths and three-toed sloths, named for the claws on their front feet. You may have heard that sloths are a kind of monkey. In fact, sloths are related to anteaters and armadillos, not to monkeys. Giant ground sloths lived in the Americas long ago and are now extinct. The biggest giant ground sloths stood about 12 feet (3.5 meters) tall and weighed several tons.

Words to know

• chambers: stomach parts
• shiver: shake
• algae: green growth
• bacteria: tiny living things