Sloths are slow because their leaf diet gives them little energy and their bodies use energy very slowly, yet a three-toed sloth climbs down from its tree about once a week to go to the bathroom. The trip is risky and costs energy, and scientists have long wondered why sloths do it. When a sloth goes to the bathroom, it can pass up to about one-third of its body weight. About half of all sloth deaths happen when a sloth is on the ground, where it loses the camouflage of the leaves, and on the ground, sloths cannot really walk, so they drag themselves along with their claws and front legs.

A sloth's fur is home to moths, beetles and other tiny animals. Sloth hairs have grooves or cracks where algae can take hold and grow. In 2014, scientists led by Jonathan Pauli reported that moths live in sloth fur, lay eggs in sloth droppings, and may help algae grow on the sloth. Three-toed sloths had more moths, more nitrogen and more algae in their fur than two-toed sloths. The green algae help a sloth blend in with the green leaves, and sloth fur is long and thick, so sloths look bigger than they are. Moving slowly helps sloths go unnoticed by hunters that find prey by sight, and sloths are hunted by big birds and big cats, such as harpy eagles, jaguars and ocelots.

Algae from sloth fur may be extra food for sloths: in lab tests the algae were highly digestible and up to five times richer in quick-energy fats (lipids) than a sloth's usual leaves. Sloths mostly eat leaves, and leaves give sloths very little energy. Sloths eat leaves from more than 90 kinds of trees, but one sloth usually sticks to about six to twelve kinds. Sloths also eat many fewer leaves than other leaf-eaters of their size: a three-toed sloth eats about 73.5 grams (2.5 ounces) of dry leaves a day, only a third of what a howler monkey eats. Because leaves stay in a sloth's slow stomach for so long, the stomach is always full, so a sloth cannot simply eat more to get more energy.

There are six species of sloth: two kinds of two-toed sloth and four kinds of three-toed sloth, named for the claws on their front feet. As of November 2026, the IUCN Red List puts four sloth species at Least Concern, one (the maned sloth) at Vulnerable, and one (the pygmy three-toed sloth) at Critically Endangered. As of November 2026, the pygmy three-toed sloth, found only on a 4.3 square kilometer island off Panama, is Critically Endangered, and only about 100 individuals are believed to remain. Giant ground sloths lived in the Americas long ago and are now extinct, and the biggest stood about 12 feet (3.5 meters) tall and weighed several tons.

Sloths live in trees, high up in the rainforest canopy, in the tropical forests of Central and South America. Sloths live alone, except for a mother with her baby or sloths that are mating, and a baby sloth crawls onto its mother's belly right after it is born and clings to her. As of November 2026, sloths depend on forests, and many forests where they live are being cut down for farms, ranches, towns and logging. Sloths cannot jump from branch to branch the way monkeys do, so they need trees whose branches touch. Cutting down forests splits sloth habitat into small pockets. Sloths cannot cross the gaps, so each small group has fewer partners to breed with.

Words to know

• lipids: fats
• digestible: easy to digest
• habitat: living place
• algae: green growth