Four fun facts about sloths


Anything that looks like a miniature, happy Chewbacca just has to be awesome—and sloths do not disappoint. From tooth to poo pellet, the creatures of Order Pilosa, Suborder Folivora are as strange and fascinating as they are adorable.

1. They don't actually sleep all that much
It is true that sloths are very still for most of the day. But that's more about self-defense than laziness. The sloth mission statement can be summed up as, essentially, "Avoid being eaten by eagles." Seriously, it's a problem.

"There's no real defense against something that's willing to dive bomb a tree, flip upside down and grab you off a vine," said Donald E. Moore, Ph.D., associate director of animal care at Smithsonian's National Zoo in Washington, D.C. "You're really better off if they just don't see you."

To that end, sloths have picked up a couple of useful adaptations. First, they're covered in a unique sort of fur that's an ideal breeding ground for algae. Second, they're able to spend most daylight hours immobile and, when they do move, it's usually very, very slowly. The result: From the air, sloths look more like green vegetation than tasty, meaty eagle snack.
So how do we know they aren't sleeping that whole time? Research. In fact, brown-throated three-toed sloths were the first animal species to have its sleeping habits studied in the wild, said Bryson Voirin, a doctoral student with the Max Planck Institute.

In 2008, Voirin was part of a team that found some wild sloths only sleep a little more than nine hours a day. To do the study, the researchers had to catch sloths, then implant electrodes just below the skin of the animals' scalps. A tiny hard drive—epoxied to each sloth's head like a hat—recorded brainwaves associated with sleep and wake cycles. The animals were also outfitted with standard radio collars. For two weeks, the sloths lived as naturally as one can with a hard drive glued to one's head. Then, the researchers picked the sloths back up, took out the electrodes and detached the electronics. The recorded brainwave data offered the sort of insight on when subjects were sleeping and when they were awake that Santa Claus only wishes he could access.

2. They're smart--and fast
Just because sloths usually move slowly, doesn't mean they're physically limited to a snail's pace. Donald Moore has first-hand experience with just how fast these creatures can go, when they really want.


One female took a dislike to me. I'm one of the only sloth biologists who's been bitten," he said. "They can use their big claws and slash out. But what she did was run at me, upside down along a vine, as fast as a cat would run along the floor. She grabbed me and pulled my hand to her mouth and then bit. It all happened very quickly."

Luckily for Moore, most of the sloths he's worked with have liked him. Some even took to grooming him. His experiences demonstrate how sloths really can tell individual humans apart from one another, and have individual personalities themselves. Social interaction isn't the only way sloths show their intelligence.

"There was a researcher in the 1930s and '40s who did vine- and rope-based maze testing with sloths and showed that they have the same level of cognitive function as a cat in a maze on the ground," Moore said.

3. Most of them can't survive in zoos
There are six species of sloths—four species of three-toed sloths and two of the two-toed variety. Of those, only the two-toed species are frequently found in zoos. It comes down to an issue of movement and diet. In the wild, two-toed sloths move more than 40 meters a day through the treetops, said Moore. Three-toed sloths move much less.

The result: Two-toers have a more varied diet—enjoying everything from lettuce, to boiled yams, to grapes. (They really, really love grapes.)

Meanwhile, other sloths eat almost nothing but parts of the Cecropia tree. Such picky eaters aren't easy animals for zoos to take care of, but it has been done. The Dallas World Aquarium, for instance, has the only three-toed sloth on display in the United States. They make it work, Moore said, because that particular three-toed sloth is very comfortable with humans—and because there are Cecropia trees in the parking lot.

"The keepers were able to take them out once a day, before the zoo opened, and let them eat from the trees in planters," he said.

4. They're in a league of their their own
Sloths evolved in South America and, for most of their existence, that continent wasn't connected to any others. They're very old—their family tree, which also includes anteaters and armadillos, diverged from the rest of the mammals some 75-80 million years ago, when South America was still joined to Africa. They're also pretty strange.

"Even the animals they're most closely related to, anteaters and armadillos, are as different from sloths as whales are from bats," Moore said.

Among the many sloth oddities is a very slow metabolism. They have the lowest body temperature of any mammal, Moore said, and they only use the bathroom once a week. That last bit has the added benefit of protecting them from predators, because their regular bathroom break is the only time sloths leave the trees. Even weirder, their digestive system is similar to a cow's, with a specialized, multi-chambered stomach that allows them to fully process leaves.

"When dogs eat leaves, they come out relatively whole. When sloths eat leaves, they come out as little pellets at the end of the week," Moore said.

Their teeth are also on the funky side. Sloths have no incisors, and no canines. Instead, they have what are called caniniform molars—conical teeth that look like triangles in cross section. From his personal experience, Moore can vouch for the fact that every side of that triangle is razor sharp.

Even the way sloths store fat is unique. Most mammals have fat deposits tucked around their bodies. Sloths, however, don't seem to, according to Moore. He's never seen an obese sloth and, in autopsies, the only place he's ever found any sign of a fat deposit is on the pads of their feet.

Image courtesy Flickr user flickrfavorites, via CC</p>


  1. I always thought the slowness was due in part to their diet, which either didn’t give them enough energy, or in some cases had natural toxins that slowed down their metabolism.

  2. Hmm. I remember reading about a species of sloth with genitalia in pairs. Like an electrical socket. I can’t find mention of it again. Was it BS, or am I just not finding that specific species of sloth on wikipedia?

  3. water rises 50′ in rainy season….sloths swim underwater ,eating for long periods.
    nobody looked in that season, only after scuba and video has it been seen.
    and they’re fast!

  4. I can’t remember where I read it, but my favourite sloth fact is that when the babies are learning to climb, they’ll occasionally mistake their own limbs for bits of tree, grab onto them and plummet groundwards.

    1. It gets even better if you grow your own ghillie suit :D Which is what sloth’s algae-stained shaggy mess is, really.

  5. One of my fond Bio-class memories is the rapturous look on a professor’s face as he recounted the privilege of being present for an extremely rare sloth dump.

    I remember him as saying that this species of sloth (whatever species that was) only took a dump once a year, but that’s probably my memory’s exaggeration. But I know he was very happy to have been there for it. Probably an important sample-collection event.

  6. Of course they didn’t sleep well with a chip on their skull and a whirring hard drive glued to their head!

  7. One of Douglas Adams’ favourite facts (and by extension, one of mine):

    Young sloths will sometimes try to grab their own limbs mistaking them for tree branches, and fall out.

    From the Salmon of Doubt.

  8. Sorry rainyrat, only just noticed you remembered the same fact. So here’s another. According to David Attenborough, they will slowly climb down a tree to defecate on the forest floor, then climb back up. No one’s quite sure why.

    1. My canoe tour guide in Costa Rica seemed pretty certain that they bury their poo to prevent getting smelled out and eaten by jaguars.

    2. Maybe the sloth realize that it is more polite to have people step in it that to have it drop from above and never figure out where it came from?

    1. I know, and such a boring deadly sin too. Stay away from Wraths and Lusts, though — those creatures can really do some damage to you…

  9. Regarding the anecdote above, I think I could handle being a sloth researcher who got attacked by a sloth. But I don’t think I could handle being the sloth researcher who got attacked by a sloth and then had to tell the EMT, “It all happened so fast!”

  10. I’ve read that due to their slow metabolism sloths can remain submerged for long periods of time, when caught in rivers during floods for instance. I believe it was something on the order of 10-20 minutes straight.

    1. I was going to mention that they hire dogs to burn down hospitals, but I see you’ve already cited my source.

      So odd that I looked up this sketch again only a few days ago. Hivemind.



      SUCK IT!”

  11. Morbid curiosity, but after reading I had to check youtube. In this case the eagle went sideways rather than upside down.

  12. is it just mean, or do sloths freak anyone else out? I mean, the slowness.. the long arms and long claws… I know they’re just waiting for their chance to spring at me and rip my throat out…

  13. Oh, Sloths and their fur-algae. That got me marked down on a paper in 3rd grade. We had to pick a rain forest animal to research and write about. I picked sloths. I did a fuck ton of research, at least for a 10 year old. I wrote about the algae on their fur that protected them from predators because that was SO COOL.

    My idiot teacher thought I made it up, and marked me down for it.

    The next months National Geographic? Yeah, it had a story about THAT EXACT FACT. Which I then brought in and threw on her desk. I totally served her.

    She never did mark me back up for that. Bitch.

  14. “he’s ever found any sign of a fat deposit is on the pads of their feet.”

    Ah yes, as with most mammals,

    The best meat is on the feet.

  15. I could climb the very highest Himalayas,
    Be among the greatest ever tennis players,
    Win at chess or marry a Princess or
    Study hard and be an eminent professor.
    I could be a millionaire, play the clarinet,
    Travel everywhere,
    Learn to cook, catch a crook,
    Win a war then write a book about it.
    I could paint a Mona Lisa,
    I could be another Caesar.
    Compose an oratorio that was sublime.
    The door’s not shut on my genius but
    I just don’t have the time!

    Flanders & Swann: “The Sloth” from “The Bestiary of Flanders and Swann”

  16. Not a “fun” fact: Most of them can’t survive in zoos.

    Just wondering how many sloths had to die to figure that one out?

  17. My favourite sloth fact (from Perth Museum’s display): sloths can swim breaststroke and backstroke, depending on which way they fall into the water.

    Depending on which way they fall into the water!

    The same display also informs me that sloths (or perhaps the particular kind of sloth on display) are useless on a flat surface, and can only pull themselves along with their toes.

  18. I’m from Brazil and I’ve always been told that sloths can really mess you up with those claws.

    When I was a kid, a relative of mine lived right by some woods and there was this one sloth that used to come down from the trees and walk around on the ground around the development. It was pretty friendly but I always kept a safe distance. Those claws were wicked-looking. :-|

  19. I know I’ve read somewhere that sloths are the only animal other than man that has sex face to face – has this been mentioned?

  20. Tom Hale,I promise you, i quick image search will reveal pics many animals(in addition to sloths and missionaries) having sex “missionary style”

  21. In evolutionary terms, it makes sense that a remarkably slow metabolism would be an alternate solution to storing fat.
    I also wonder how if the low body temperature could be a factor in how it metabolizes dietary fat.

    ie Human core temperature is above the melting point of butter, but do humans assimilate fats which have a melting point of 110 degrees Fahrenheit?

  22. And
    Has NASA ever experimented on sloths?

    I NEED to know how an animal with its entire circulatory system designed to function upside down reacts physically to prolonged living at zero Gs.

  23. The sloth in Dallas that they mention is completely out in the open, not in a cage or anything. One could touch it quite easily (I don’t know the official policy on touching though) Those claws were enough for me to keep my hands away from it though!

    I highly recommend going to the Dallas World Aquarium if you’re ever in Dallas. Now I want to stake out the parking lot.

  24. so, this is extremely disturbing to hear that scientists are epoxying hard drives to the sloths! that is wack and i feel that this is actually against what a true, earthen scientist is. /i heard there is this kind of shit happening to puffins in the Arctic regions.

    1. Come on. It’s awesome and cute at the same time, chill out. Beetles live on sloths – I don’t think a tiny hard drive will give them much grief.

      Come to think of it, SSDs would be better.

  25. Great, a pretext to share my only sloth joke:

    A sloth is making his way through the forest when he is attacked by a gang of snails. After fighting them off, he goes to the police station to report the assault. The policeman asks him to describe the attackers, and he replies: “I didn’t see much, it all happened so fast.”

  26. nephetsE: Beef fat (tallow) has a melting point of 104-114F

    Leaf Lard has a melting point of 109-118F

    Suet (the hard fat around the kidneys: usually of cattle) has a melting point of 113-122F

    Sheep fat melts at 113-130F.

    Suet congeals at 99-104F.

    The harder fats are harer to digest, because the breakdown requires digestive acids to do the work, but they are digestible (though it helps to have them in conjunction with other food which slow the process and do keep them in the got for a longer period of time.

  27. How do you know so much about sloths? They seem like wonderful creatures. It sounds like the one who bit the researcher did it was a warning – actually reaching out, grabbing his arm & biting him seems like the way a human would do it.

  28. I remember seeing sloths way up the Amazon River……and actually ‘petting’ one in Manaus (in captivity). They are amazing creatures and have fascinated me ever since.


  30. This is a poem I just learned(I’m in 5th grade).
    The Sloth by Bobbi Katz
    A living cradle in my tree,
    It’s usually snoozle time for me.
    A bag of fur with hooks for toes,
    That’s the way a sloth’s life goes.
    I nibble on a leaf or two,
    It’s such slow work to chew and chew.
    My eyes spy a slice of sky,
    The wind sings me a lullaby.
    Softly my eyes close and then,
    I drift off to sleep again.
    Let the monkeys leap and run,
    My lifestyle’s not for everyone.
    I’m not as lazy as I seem,
    I have so many dreams to dream,
    So very many dreams to dream.

  31. my wife is from the jungles of la moskitia in central america and had a sloth for a pet. She said, and her father confirmed, that they spend “a part of their life living in water and when they come out they look and smell horrible. They turn completely green.” To her it was a kind of metamorphosis. I didn’t believe her at all but apparently they don’t mind the water?

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