The sloth’s head is short and flat, with a snub nose, rudimentary ears, and large eyes. They possess a short, fine undercoat and an overcoat of longer, coarser hairs, which turn green in moist conditions due to algae growth. This greenish tint camouflages them in the forest canopy. Their fur also harbors moths, ticks, and beetles. Unlike most animals, the sloth’s fur is parted on the belly and curves across the back, allowing rain to run off.
Sloths range in size from 21 to 29 inches. They weigh between 9 and 18 pounds when fully grown. As its name suggests, the two-toed sloth has two claws on each forelimb, while their hind feet have three toes with hook-like claws. These claws measure 3 to 4 inches long, perfect for hanging onto tree branches and grabbing leaves and shoots to eat. Because sloths are so light weight, they can feed in high, narrow branches that won’t support other animals, like jaguars and ocelots—predators of the sloth.
Sloths are nearsighted, relying little on vision to carry out normal patterns of behavior. They also have poor hearing. However, they have a great sense of smell thanks to extremely well-developed olfactory bulbs.
At first glance the sloth may seem slow and lazy; however, their usual idleness is due to metabolic adaptations for conserving energy. (Their metabolic rate is 40 to 45% of that expected for a mammal of their size.) Leaves, their main food source, provide very little energy or nutrients, and do not digest easily. Sloths, therefore, have large, specialized, slow-acting stomachs with four chambers in which symbiotic bacteria break down the tough leaves. As much as two-thirds of a well-fed sloth’s body weight consists of the contents of its stomach, and the digestive process can take as long as a month.
Sloths also maintain low body temperatures when active (86 to 93 °F) and still lower temperatures when resting. If a sloth’s body temperature drops too low, the digestive bacteria in its gut can stop working, and the sloth can starve to death even with a full stomach.