SCIENCE

Besides the risks three-toed sloths incur on their tri-weekly potty trips, the trips are costly in terms of energy demands. Why, scientists wondered, do sloths expend so much energy just to poop? (National Geographic News Watch)

Use our resources to better appreciate sloths and the people who love them.

David Attenborough is one of those sloth-loving people.

Discussion Ideas

• Read the Nat Geo News Watch blog post, then watch our delightful video of Nat Geo Emerging Explorer Lucy Cooke. Fast forward to about 7:56, when she talks about developing a love for sloths. She says some people think sloths are “lazy and stupid and dirty.” Why do you think sloths have this stereotype?
  • Their name is sloth, for goodness’ sake. Sloth, one of the seven deadly sins in the Christian tradition, is defined as “physical or mental inactivity; disinclination to action, exertion, or labour; sluggishness, idleness, indolence, laziness.” (It’s also the collective name for a group of bears—a gaggle of geese, a host of angels, a sloth of bears. I love the OED so much it hurts.)
  • Sloths are v e r y slow-moving, which might indicate laziness. As the scientist quoted by Nat Geo News Watch says, this is a misunderstanding. Three-toed sloths mostly eat leaves, which “don’t contain a lot of calories or nutrition, which means that sloths have to conserve their energy to survive on a relatively low-nutrient diet. They aren’t so much lazy as they are energy efficient.”
  • Sloths might appear dirty because their slow-moving behavior allows organisms such as algae and moths to live in their fur. As the Nat Geo News Watch blog explains, this isn’t unhygienic—it’s an evolved symbiotic (mutualistic) relationship.

• What is the relationship between the three-toed sloth, pyralid moths, and algae? Read our introductory page on food webs to get an idea.
  • The sloth’s body is a micro-habitat with its own food web. Follow the sloth-to-moth web below.
    • Three-toed sloths eat leaves—they’re one of the largest tree-based herbivores in the world. (Here’s another example on the other side of the ocean.) Leaves are very low in protein and nutrients, so three-toed sloths supplement their diet with algae. They don’t have to look very far or work very hard to find it.
    • Algae, a nutrient-rich producer, grows in sloth’s fur. Biologists aren’t quite sure how the algae gets there, but it has something to do with the algae’s sloth-fur neighbors, pyralid moths.
    • Pyralid moth larvae incubate in sloth poop and, after they’ve hatched, the moths live in sloth fur. “Insect droppings could be seeding sloth fur with extra nitrogen, or the moths could be transporting the sloth’s own dung back to the animal,” according to the Nat Geo News Watch post.

• Three-toed sloths are notoriously difficult to maintain in zoos or other captive-breeding facilities. Few have survived more than a month. How might the new discovery of the moth-to-sloth food web help explain this?
  • Pure speculation and hypothesis: Zoos and zoo animals are usually kept very clean. This “highly sanitized environment” might not support the dynamics of the moth-to-sloth food web. For instance, zoos might not be allowing sloth poop to slowly decompose and incubate pyralid moth larvae. Fewer moths could then colonize “cleaner” sloth fur, reducing the amount of algae available to supplement a sloth’s diet.