Tree leaves tend to be coarse and difficult to digest, full of tough cellulose and protected by toxic chemicals produced by trees to ward off their predators. In this war between plants and the animals that would eat them, sloths have succeeded through adaptations that enable them to be leaf-eaters, or folivores. Furthermore, they do their leaf-eating on the crowns of mature trees, only infrequently coming down to the ground, so they are called arboreal folivores. The story of their adaptation to the canopy of the forest and to leafy food supplies is an unusual one.
Sloths have long, shaggy fur that they groom carefully every day.
Two species of sloth are found on BCI, living in the same habitats, and sometimes on the same tree. Both species have shaggy fur that is slightly greenish, long hooklike claws on their front and hind feet, and they usually move very slowly and spend most of their lives hanging upside down. Three-toed sloths, which are very common and may be the most numerous species on the island, have been estimated by Dr. Gene Montgomery to number about 8,000. They can be active both day and night, and tend to stay in the same tree for a day or more and move short distances. They have a smiling face with a dark mask around the eyes, weigh up to about 6 kg, and have a short tail.