A three-toed sloth spends almost its entire life hanging from a tree, safe from danger. But every week it comes down to the forest floor to defecate, right where jaguars, ocelots, and eagles lie in wait.
For years, no one understood why they took such a risk for something they could do from the branches.
In 2014, researchers from the University of Wisconsin-Madison, led by Jonathan Pauli and M. Zachariah Peery, proposed an answer: Cryptoses choloepi moths live in the sloth’s fur, losing the ability to fly forever as soon as they settle there and depending on fresh excrement to lay their eggs.
In return, these moths enrich the algae that grow in the animal’s fur with nitrogen—algae that provide camouflage and could supply it with nutrients.
It’s a silent alliance that lasts throughout the 30 years a sloth can live in the wild, although the price of maintaining it is venturing out to risk its life once a week.