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.
"While we don’t know exactly how they are doing this ... but to our knowledge this is the first physiological evidence of a mammal quickly invoking reversible metabolic depression without entering a state of torpor [or] hibernation," Rebecca Cliffe, founder of Sloth Conservation Foundation, told National Geographic.
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 allows them to 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.
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 long time 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.
Wired writes, "Sloths are xenarthrans – their closest relatives include anteaters and armadillos. And, among other things, large, curved claws and powerful forelimbs for digging are common xenarthran traits."
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. As National Geographic notes, "Though they couldn't be clumsier on land, sloths are surprisingly good swimmers. They sometimes fall directly from rain forest trees into rivers and stroke efficiently with their long arms."
6. Sloths can keep their grip on a tree branch 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. "[W]hen hanging upside-down in a tree, they are held in place by the claws themselves and often do not fall down even if shot from below," notes Wikipedia.
And there are other areas where that firm grip comes in handy, like this reunion between a mom and a baby sloth:
Editor's note: This article has been updated since it was originally published in January 2017.