The real story
Three-toed sloths spend almost their whole lives in the canopy, yet they climb all the way down roughly once a week to defecate at the base of a tree, where predators like jaguars can catch them. They can lose a large share of their body weight in a single trip. Why they bother has puzzled biologists for decades.
One explanation involves their passengers. Moths that live in sloth fur lay their eggs in the dung; the new moths fly up to find a sloth, and their bodies add nutrients to the fur, which feeds the green algae growing there. The algae helps camouflage the sloth and may even be licked as a snack. Off the ground, sloths are also surprisingly good swimmers.
