8 Fast Facts About Sloths

Get up to speed on these unique and adorable mammals.

three-toed sloth climbing in a tree
There are two living families of sloths: two-toed and three-toed (pictured). Jaymi Heimbuch

Sloths are typecast for being slow. But while sloths are a bit sluggish compared with most mammals, that is hardly their only noteworthy trait. Here are a few other things worth knowing about sloths.

1. They Move Slowly for a Reason

Sloths are known for barely moving, and there's a good reason for that. In a study published in PeerJ, researchers at the Sloth Conservation Foundation discovered that sloths' metabolism shuts down when the weather is too hot or too cold. Because sloths only eat leaves from a few trees, their diet is very low in nutrition. Therefore, they can't expend a lot of energy to regulate their body temperature.

A similar earlier study by German researchers found that although the locomotion of sloths is similar to other mammals, such as monkeys, their anatomical structure is different. They have very long arms, but very short shoulder blades, allowing them to have a large reach with very little movement. That lets them save energy while making the same movements as other animals.

2. Sloths and Moths Help Each Other Out

Sloths are an ecosystem in and of themselves, and they have a mutually beneficial relationship with moths, according to research published in the Proceedings of the Royal Society B. Sloths allow algae to grow on their fur, which acts as camouflage for life among the green leaves of the jungle canopy and also as an extra source of nutrition. (Yes, they eat it.) The moths help the algae grow, and in return have a home on the sloth itself. Indeed, sloth moths have evolved to live nowhere else but in sloth fur.

3. Sloths Come Down to the Ground Once a Week to Poop

sloth walking on sandy ground
Sloths only venture out of trees when necessary. Stefan Messing/EyeEm/Getty Images

Sloths have a very slow digestive system, and they only need to leave the tree canopy to use the bathroom once a week. But there's more to the story than just the interval between bathroom breaks.

For a long time, it puzzled researchers why sloths bothered to come down to the ground to defecate, when it's both energy intensive and makes the sloth vulnerable to predation. Well, here's where those moths come into play. Sloth moths lay their eggs in sloth poop. Coming down from the canopy to do their business benefits the moths, which in turn benefit the sloths with that algae growth the sloth needs for an extra nutritional boost. So, the long trip down to the bathroom is a more complex behavior than meets the eye.

4. They're Related to Anteaters and Armadillos

Sloths have some surprising relatives. While the distant family members don't look similar at first glance, a clue lies in those famously long claws.

Sloths are among the 31 living species of xenarthrans, and their closest relatives include anteaters and armadillos. Among other things, common traits of this mammalian clade include large, curved claws and powerful forelimbs for digging.

5. Sloths are Great Swimmers

They may move slowly among the trees, but sloths are impressive and speedy swimmers. They swim with an efficient breast stroke that helps them move to new parts of the forest, necessary for foraging or finding a mate.

6. Sloths Can Keep Their Grip on a Tree Even After Death

Sloths are so good at hanging upside-down from trees with their perfectly curved claws that they sometimes can continue to hang from a branch even after death. If an animal is trying to hunt a sloth, it may need to scale a tree to retrieve the quarry.

7. Some Sloth Species Were Once Enormous

Millions of years ago, Earth was home to giant ground sloths, some of which grew as big as elephants. They could measure 20 feet (6 meters) long from snout to tail; the species Megatherium americanum, for example, was up to 10 times the size of living sloths. Despite their large size and intimidating claws, however, these giants sloths were also vegetarians. They may have been driven extinct at least partly by pressure from human hunting.

8. Sloths Get a Lot of Sleep

Sloths are primarily nocturnal, sleeping during the day and coming out at night to forage in the trees. They're known for getting lots of rest, sleeping roughly 15 to 20 hours per day. They often sleep curled up in the fork of a tree, but may also doze while hanging from a branch by their claws.