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The Mystery of the Sloth Poop

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Three-toed sloths are just that: three-toed, and slothful. They live high in the tree canopy and feed exclusively on the foliage there, hanging around most of the time and moving slowly when they move at all. 

They only descend from their leafy home once a week to make a bathroom run. After shimmying down the trunk of a tree, a sloth digs a small hole in the dirt, poops in it, covers their makeshift toilet with leaves, and then climbs back up. This is not the most efficient way to poop, nor the safest. Climbing down a tree to ground level and then back can cost a sloth as much as 8 percent of its daily calorie intake, and the animals are out of their element and incredibly vulnerable on the ground—more than half of all recorded sloth deaths are caused by attacks from predators at or near the ground. 

If a simple poop can cost a sloth its life, why do it like that? The three-toed sloth’s cousin, the two-toed sloth, simply defecates from the canopy. It can’t be pleasant to be standing underneath one when that happens, but the sloths are safer for it. If three-toed sloths keep making these costly and risky trips to a ground-floor bathroom, there must be something that makes the trip worth it. 

Scientists have come up with a few possible benefits for ground-pooping, like fertilizing the trees that the sloths call home or revealing their locations to other sloths so they can mate (how romantic). Ecologist Jonathan Pauli and other researchers from Wisconsin and Virginia have a different idea, though, that’s rooted in the sloth’s dietary problems. 

Sloths are among the 0.02 percent of mammals that are specialized arboreal herbivores, living in trees and foraging for food there. This lifestyle isn’t an easy one. To live on a tree branch, you have to be relatively small and light, but a limit on body size also puts a limit on how much you can digest. A sloth’s main source of food, leaves, is pretty nutrient-poor and not easy to digest to begin with, so they’re under some serious nutritional constraints. Pauli and his team wondered if, when sloths went downstairs to use the bathroom, they were also grabbing some extra food. 

The key here is the miniature zoo that sloths carry around with them. Their thick fur is home to all kinds of algae, fungi, arachnids and insects. Among these tenants are moths from the genus Cryptoses, commonly (and adorably) called “sloth moths.” These moths are absolutely dependent on their host sloth’s weekly bathroom trip. The females lay their eggs in the sloth dung, which the larva then live off of until they become adults and can fly upward to move onto their own sloth. Maybe the sloths are just as dependent on the moths, and aid their lifecycle because the bugs are somehow nutritionally important. 

The researchers took locks of hair from the ground-pooping brown-throated three-toed sloth and from Hoffmann’s two-toed sloth, which prefers a “bombs away” style of defecation. After removing and counting the moths from each hair sample, they looked at the nutrients available in the hair and then compared them to some sloth stomach contents to see if there was any connection between the moths, the contents of the hair, and what the sloth had been eating.

They found that sloths that had more moths on them also had more nitrogen-rich hair and more algae growth. The algae also turned up in the sloths’ stomachs, and when the researchers analyzed it they found that it was easily digestible and rich in carbs, proteins, and fats. 

So the perilous pooping process keeps the moths around. Moths mean more nitrogen (why, exactly, is still an open question—the moths might be dragging the nitrogen up from the sloth poop or releasing it when they die). More nitrogen promotes more algae. And algae seems to be a good nutritional supplement—though the researchers haven’t crunched the numbers to see just how much energy and nutrients the algae could provide. It’s a roundabout way to get a meal, but whatever works. Two-toed sloths, by the way, are less fussy eaters, and will forage a wider area, which may explain why they can poop from the canopy—they don’t need the moths or the algae that comes with them. 

There’s one big problem with all of this, according to other sloth researchers: There’s little evidence that the sloths are eating the algae from their hair. No one has seen them licking their fur or pawing at it in a way that suggests they’re picking the algae out for a snack. The study found bits of algae in sloth stomachs, but no one’s even sure if it's enough make any real nutritional impact. 

Becky Cliffe, a zoologist working at the Sloth Sanctuary of Costa Rica, doesn’t think the algal snacks are worth the risk of a climb down a tree, because sloths can get along fine without them. “For a start, sloths in captivity that are fed a natural diet but don’t have any algae are perfectly healthy,” she writes. “Blood analysis done at the Sloth Sanctuary shows no difference between these captive animals and their wild, algae-covered counterparts.”

Even if the sloths are chowing down on algae when no one is looking, it doesn’t seem to be so integral to their diet that they’d risk time on the ground. For now, the way a sloth poops remains one of the great mysteries of the rainforest. 

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Big Questions
Do Cats Fart?
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Certain philosophical questions can invade even the most disciplined of minds. Do aliens exist? Can a soul ever be measured? Do cats fart?

While the latter may not have weighed heavily on some of history’s great brains, it’s certainly no less deserving of an answer. And in contrast to existential queries, there’s a pretty definitive response: Yes, they do. We just don’t really hear it.

According to veterinarians who have realized their job sometimes involves answering inane questions about animals passing gas, cats have all the biological hardware necessary for a fart: a gastrointestinal system and an anus. When excess air builds up as a result of gulping breaths or gut bacteria, a pungent cloud will be released from their rear ends. Smell a kitten’s butt sometime and you’ll walk away convinced that cats fart.

The discretion, or lack of audible farts, is probably due to the fact that cats don’t gulp their food like dogs do, leading to less air accumulating in their digestive tract.

So, yes, cats do fart. But they do it with the same grace and stealth they use to approach everything else. Think about that the next time you blame the dog.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Squirrels Are Probably More Organized Than You, Study Finds
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Despite having a brain that's slightly bigger than the size of a peanut M&M, squirrels have a fascinating, razor-sharp instinct when it comes to survival. They know that acorns that are high in fat and sprout late are perfect for long-term storage, so they salvage them for winter and eat the less nutritionally dense white-oak acorns right away. They also tend to remember where they put their acorn stash rather than relying solely on smell. Like nature's perfect stunt performer, they can even fall out of trees in a way that minimizes physical damage. Now, researchers at the University of California, Berkeley have unveiled a newly discovered part of a squirrel's hoarding strategy, Atlas Obscura reports.

The researchers tracked 45 wild fox squirrels on the UC-Berkeley campus for nearly two years. They made available to the squirrels four different types of nuts—walnuts, pecans, almonds, and hazelnuts. Sometimes the animals were given a single type of nut, and other times the nuts were mixed. Either way, the squirrels promptly sorted and stored their food according to type—walnuts went in one hiding place, almonds in another, and so on.

This type of behavior is known as "chunking" and makes it easier to retrieve data in memory. In doing this, a squirrel won't have to visit several different places looking for pecans: They know just where the main supply is. Squirrels can stockpile up to 10,000 nuts a year, so it's essential for them to know which type of nut is where.

The study, published in Royal Society Open Science, also indicated that squirrels seem to understand nuts have weight, choosing to carry heavier acquisitions to a different location than lighter nuts.

Squirrels being squirrels, they were happy to be gifted an assortment of nuts during the experiment, but there was one wrinkle: Rather than stash them away, sometimes they'd just eat them on the spot.

[h/t Atlas Obscura]

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