Correction appended Jan. 23, 2014 Among the greatest mysteries of the tropical rainforest are the pooping habits of sloths. Really. Those furry, slow-moving tree dwellers almost never descend from the safety of the tree tops—except for once a week, when nature calls. It’s a dangerous and often lethal potty break. On the forest floor, they are spectacularly vulnerable to predators, and the question biologists have been asking for years is, why descend at all? What possible benefit could make this life-or-death journey better for the sloth than simply cutting loose, as it were, from the safety of a tree? Theories abound: Maybe the sloths are somehow picking up minerals from the soil that their leafy diets don’t provide them. Maybe they are fertilizing their favorite trees with their poop. Or maybe it has to do with the other species that call the sloths themselves home. Sloth fur is populated by colonies of moths and flourishing coats of green algae. The moths are known to leap onto sloth poop to lay their eggs before returning to their host when the bathroom break is through. But symbiosis being what it is, there ought to be some benefit to the sloth from this arrangement too. Like many sloth scientists, Jonathan Pauli, an assistant professor at the University of Wisconsin, Madison, has pondered the poop question in his free moments. In this week’s Proceedings of the Royal Society B, he and his colleagues present data suggesting that the moths may indeed be helping the sloths, by somehow feeding the algae in their fur, which the sloths in turn might be eating to supplement their diet. Pauli’s has long studied the population dynamics of radio-collared sloths in Costa Rica, and the riddle of the weekly poop treks had always puzzled him. Sloths don’t eat the moths, eliminating one obvious explanation for their willingness to tolerate their guests and brave the forest floor for them. And the moths themselves, which Pauli says are little more than “flying genitals” by the time they reach maturity, don’t produce their own … Continue reading The Mystery of Sloth Poop: One More Reason to Love Science