Sloth, an extremely slow-moving mammal native to the forests of Central and South America. The sloth has a small, round head. The toes of its limbs end in strong, curved claws. Its most notable characteristic is that it spends much of its life upside down, hanging by the claws of all four of its limbs from the branches of a tree. Tiny green organisms called algae grow on the sloth's hair, giving it a greenish color and causing the animal to blend in well with its leafy surroundings.

The slothThe sloth has a small head and strong, curved claws.

Sloths usually sleep during the day, either curled up in the fork of a tree or hanging from branches. At night, they move about in the tree, slowly feeding on leaves, flowers, or fruits. Because its feet curve inward, a sloth is unable to walk with ease upon the ground and will descend a tree only to get to another tree in search of food. In such a case, it either shuffles clumsily about on all fours or drags itself by its forelimbs across the ground. The chief enemies of sloths are eagles and jaguars. Some sloths breed in the spring while others breed throughout the year. The female generally gives birth to one young.

There are two genera of sloths—the three-toed sloth, or ai; and the two-toed sloth, or unau. Both have three toes on their hind limbs, but differ in the number of toes on the forelimbs. The three-toed sloths, of which there are three species, have small, stumpy tails and a body length of up to about 20 inches (50 cm). The two-toed sloths, of which there are two species, are tailless and grow up to about 25 inches (64 cm) long. Almost all other mammals have seven vertebrae in their necks, but three-toed sloths have nine and two-toed sloths have six.

Sloths make up the family Bradypodidae. The three-toed sloths make up the genus Bradypus, the two-toed sloths make up the genus Choloepus.