Sloths go to the ground to urinate and defecate about once a week, digging a hole and covering it afterwards. They go to the same spot each time and are vulnerable to predation while doing so. The reason for this risky behaviour is unknown, although some believe it is to avoid making noise while defecating from up high that would attract predators.
Consistent with this, they reportedly relieve themselves from their branches during storms in the rainy season.Another possible explanation is that the middens provide the sloths with one of their few methods of finding one another for breeding purposes, since their sense of smell is far more acute than their eyesight or hearing.Still other recent studies have suggested that it might be relevant for maintaining the ecosystem in the sloths' fur.
Idividual sloths tend to spend the bulk of their time feeding on a single "modal" tree; by burying their excreta near the trunk of that tree, they may help nourish it.Recently there has been some speculation that sloths go to the ground to defecate because of their mutually beneficial relationships with moths. While the sloth defecates, female moths that otherwise live on a sloth will get off and immediately lay their eggs directly on the fecal matter, on which the larvae survive until they mature to adulthood and are able to fly onto sloths. Incidentally, it appears that sloths benefit from their relationship with moths because the moths are responsible for fertilizing algae on the sloth, which provides them with nutrients.