The sloth’s busy inner life

Written by: Lisa Stelzner

Primary Source: Lisa Stelzner

Three-toed sloths are not just unusual animals for moving so slowly.  Their fur actually contains an entire ecosystem of organisms! Sloths have algae that grow in their fur (specifically, in grooves and channels in their hair) and a species of moth that burrows in its hair (perhaps up to 100 moths on a single sloth!). What is fascinating is that the three-toed sloth’s behavior is influenced by the moths and algae. See, the sloth comes down from the trees once a week to defecate, and actually digs a hole and covers the poop with leaves.  The problem is, the sloth is very vulnerable to predators while it is on the ground (half of sloth deaths occur there).  Researchers could not understand why the sloths wouldn’t just defecate from up in the trees, where they could stay safe. In contrast, two-toed sloths do not come to the ground.

The moths that live on the two-toed sloths are coprophagous, which means that they consume poop.  They lay eggs in the poop when the sloth comes to the ground, the larvae consume it, and after becoming adult moths, they fly to the trees to find sloths.  In the fur, they lose their wings, mate and die.  Fungi and bacteria in the fur break the moth’s bodies down, and supply nitrogen to the algae that grow in the sloth’s fur.

So why does the sloth care about the moths and algae that live on it?  It’s because sloths eat leaves that provide little nutrition, and with their small guts, they need to get more nutrients somehow.  It turns out that they eat the algae!  (Algae have been found in sloth’s stomachs.)  This means that technically, the sloths are farming the algae on their own bodies.

In another article, scientists have recently discovered that the fungus in sloth’s fur may provide an important new drug for Chagas’s Disease, which has been very difficult to treat.  Also, if you want to see an adorable video of baby sloths being washed, it is embedded in the article!

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Lisa Stelzner
I'm a plant biology PhD student studying monarch butterflies in Michigan, but I'm interested in lots of other types of science, too. I am interested in how breeding monarch butterflies choose their habitat based on floral species richness and abundance. Few studies have been conducted on optimal foraging theory when it involves an organism searching for two different kinds of resources, and butterflies are an ideal study system to investigate this, since many species are ovipositing specialists and only lay eggs on one species of hostplant, but are feeding generalists and nectar from a broad variety of flowering forbs.