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February 21, 2014

What Lives On A Sloth

There is a small, furry creature creeping at a snail's pace up in the branches of the cacao trees of Costa Rica (found in various regions of Central and South America)!  It's a three-toed sloth! Like all creatures, this sloth has an amazing life-story to share with you, but we only have enough space here to hear one tale.  I read a story about a scientific study in the New York Times about why three-toed-sloths make a dangerous journey to the forest floor.  Being a good journalist I had to ask the sloth a rude question to see if the story was true.  I asked, "Why do you only go to the bottom of the tree once a week just to go to the bathroom?"  (Ever seen a sloth blush?  Neither have I.  They're very composed afterall.)  Let's listen to the sloth's response.

Hello?  Hello?  Can you hear me?  This is Sloth here.  No up here.  Look up higher in the trees.

Credit: New York Times

Hello there.  I do say that's not a very couth question to ask a respectable sloth like me, but if you insist on knowing I'll tell you. 

We sloths are very slow.  A normal speed for us is about .15 mph and we have a tendency to be a bit snoozey, sleeping 15-20 hours a day.  Don't laugh, it's not that we're lazy.  No, no, no.  You see we have a very restricted diet of leaves and leaves aren't very nutritious.  Not to mention, many of them are toxic at that.  Because we live off of plant matter we have to let the leaves ferment in our guts; that means that we have to wait for microorganisms like bacteria, archaeans and fungi to break it down into little bits that we can digest.  In fact, we have the slowest metabolism in the whole mammal class.  It's the lack of nutrition and our slow metabolism that cause us to move so slow.

So, you wonder, if we three-toed-sloths are so slow, why do we leave the safety of the trees once a week to go to the bathroom at the forest floor when feral dogs, coyotes and panthers could so easily snatch us away (1/2 of all our deaths occur on the ground afterall)?  Firstly, we need to separate ourselves from our two-toed-sloth cousins who never leave the safety of the trees to go #2.  Look out below!  But that is because our two-toed cousins move a little faster than we do and they eat a more diverse diet than just leaves including fruits and animals.  On the other hand, we three-toed-sloths, if you remember, have a very poor diet of just leaves.  We leave the safety of the trees for the sake of our diet you could say.

Scientists used to think we were just fertilizing our favorite trees.  Ha Ha Ha.  But the real reason is that when we climb down the cacao trees and go to the bathroom a whole bunch of moths come out of our fur and lay their eggs in our poo.  P U!  I hope they plug their noses.  When the moth eggs hatch the larvae eat the dung to grow.  When the larvae are full grown they go flying up into the canopy of the forest to find one of us three-toed-sloths to call home.  You see, these moths are special moths to us.  They live nowhere else in the world, except in our fur.  That makes them pretty special and us pretty special too.  When we groom, our claws move so slow that the moths can move out of the way without being harmed and over 100 of those moths can be living in the fur of just one of us!

Why are there moths living in our fur you might ask.  Well as it turns out, when they die in our fur the bacteria and fungi on our body decompose them into nutritious molecules that are nitrogen rich, but we don't eat that.  Rather, the algae growing on our fur absorb the nitrogen compounds and other nutrients.  Our fur is great for growing algae; it has little cracks that collect water when it rains.  Algae like living in water and because our hairs collect water in those little cracks, the algae like living on and in our hairs where the water is.  The algae growing on our fur kind of gives some of us a green tint. 

Credit: pitt.edu
Now this is where it gets tasty and this completes the long answer as to why we climb down trees at great personal risk to go to the bathroom once a week.  If you weren't following because you're snoozey likes us, let's recap.  We three-toed-sloths have moths that are found nowhere else in the world living in our fur.  When we go poo they lay their eggs in the dung and then climb back aboard as we climb back up.  When their eggs hatch and their larvae have grown into moths, they fly up into the trees looking for one of us to live on.  When one of these moths dies in our fur it is decomposed by bacteria and fungi that live on our bodies too.  The algae growing in the rainwater-filled cracks of our hairs absorb the nutrients released by the decomposition of the moths.  You could say we're growing an algae garden on our fur, because we eat that algae.  That's right, we eat the algae that grows on our fur.  Why?  Because, though algae has about the same amount of carbohydrates and protein content as plant leaves, it is much richer in lipids, and this gives us energy.  So, we supplement our nutrient-poor and energy-poor diet of leaves with our algae gardens.
That's it.  That's why we climb down our cacao trees to go to the bathroom even though there's a great risk that we'll get eaten by panthers, coyotes and feral dogs down there.  Friends will make you do crazy things, but the truth is that our moths would go extinct if we didn't make that trip so that they could lay their eggs.  And without those moths living in our fur, we wouldn't be able to grow algae gardens to supplement our poor diets and we might starve. 
Credit:  New York Times

So there you have it.  Crazy isn't it, who we need in this world to survive.  What we have to do to help others and to receive in turn.  Maybe we need each other in some peculiar, convoluted way too?  See you later!  Thanks for listening!  You know where to find me; just look up and I'll be hanging around in my cacao trees.

Credit: World Land Trust

-Seth Commichaux


New York Times.  The Sloth's Busy Inner Life.  Nicholas Wade.  January 28, 2014.

Proceedings of the Royal Society.  Jonathan Pauli, Jorge Mendoza, Shawn Steffan, Cayelan Carey, Paul Weimar, Zachariah Peery.  A Syndrome of Mutualism Reinforces the Lifestyle of a Sloth.  2014. 



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