Sloths move slowly because their leaf diet gives little energy and they have a very low metabolism that conserves energy.
Reasons
- Diet: sloths eat leaves, which are low in calories and slow to digest. A meal may take 2 to 4 weeks to digest.
- Low metabolic rate: about 40 to 45 percent of the rate expected for their size.
- Low muscle mass: about 25 to 30 percent of body weight, compared with 40 percent in most mammals.
Speed
On the ground, sloths move about 0.1 mph (0.15 km/h). In trees, about 0.15 mph.
Benefit
Slow movement helps avoid predators like harpy eagles and jaguars.
Habits
They descend to the ground about once a week to defecate.
Fur
Algae grow on their fur, giving a green tint for camouflage.
Species
Two-toed and three-toed sloths of Central and South America.
Reasons
Sloths move slowly because their diet is low in energy and they have a very low metabolism. They eat leaves, which are low in calories and difficult to digest, and their stomach has multiple chambers with bacteria that take 2 to 4 weeks to digest a single meal. Their metabolic rate is about 40% to 45% of what would be expected for an animal of their size, the lowest of any non-hibernating mammal.
Speed
On the ground sloths move about 0.24 kilometers per hour (0.15 mph), or about 4 meters per minute. In trees they move faster at about 0.4 kilometers per hour. They climb with strong curved claws, 7 to 10 centimeters long. Three-toed sloths can also swim well, using their long arms, at about 13.5 meters per minute.
Benefit
Moving slowly helps sloths avoid predators such as harpy eagles, jaguars and ocean snakes, because they are hard to spot. They save energy, and since leaves provide so little, slow movement is a survival strategy. Their body temperature is low and variable, 30 to 34 degrees C, and they cannot shiver well to stay warm.
Habits
Sloths spend most of their life hanging upside down in trees. They sleep or rest 15 to 20 hours a day in the wild (captive sloths sleep longer). They come to the ground about once a week to defecate, a risky trip, in which they bury waste at the base of a tree. About 60% of sloth deaths from predators occur during these trips. Their muscles are about 30% less than other mammals of their size, so they cannot walk upright and drag themselves with their arms.
Fur
Sloth fur grows in the opposite direction from most animals so that rain runs off the belly as they hang. Algae grow on the fur and give it a greenish tint, which acts as camouflage. Sloth moths live in the fur. Their fur harbors an ecosystem of beetles, mites and fungi.
Species
There are six living species: two-toed sloths (Linnaeus’s and Hoffmann’s) and four three-toed sloths (brown-throated, pale-throated, maned and pygmy). The pygmy three-toed sloth is Critically Endangered and found only on Isla Escudo de Veraguas in Panama. Sloths live in Central and South America. Giant ground sloths, some as large as elephants, went extinct about 10,000 years ago.
Metabolism and physiology figures
Sloths have a very low metabolic rate, about 40 to 45 percent of what is expected for mammals of their size, and they eat leaves that give little energy. Their main digestion takes 2 to 4 weeks, and a meal’s contents can account for up to a third of their body weight. Sloths move about 0.15 mph (0.24 km/h) on the ground, but they swim well. They descend to the ground about once a week to defecate, a risky trip, as most predation happens then. Their fur hosts green algae that provides camouflage, and moths and beetles live in it. Sloth muscle mass is about 25 percent of body weight, compared with 40 percent in most mammals, so they cannot walk well but cling strongly. Two toed and three toed sloths live in Central and South America, and some species such as the maned three toed sloth are listed as vulnerable.
Based on data from the IUCN and the Smithsonian’s National Zoo
