The Smithsonian Channel visited Gorgona Snake Island off the coast of Colombia to understand the remarkable symbiotic ecosystem that lives within the uniquely hollow hair follicles of resident sloths. These particular sloths, who were originally marooned on this island, move much more slowly than those in more highly popular areas due to a lack of viable nutrients within the area. This low level of activity allows the ecosystem to thrive.
He keeps still for so long his fur has developed its own mini ecosystem algae is the first organism to colonize his hollow hair follicles. The simple single-celled organisms give his fur a greenish tinge perfect camouflage in the canopy. …The algae also feeds a species of moth unique to the sloth…Every member of this community benefits the other. The moths fertilize the sloth’s fur with their nutrient-rich droppings that in turn encourages more algae to grow which helps protect the sloth through camouflage.
The growth pattern of their fur also lets the sloths to drip dry after the rain.
In mammals, hair parts grow along the spine and flow down the back to the belly. Because sloths spend most of their life upside-down in the trees, its fur grows the other way–belly to back–allowing it to drip dry from the rain.