Sloths Have The Camoflauge Thing Down!
A level of camouflage for the sloth is the coating of algae which it cultivates in its fur. These symbiotic organisms find the moist and warm environment of sloth hide perfect for growth. Normally, being slimed by algae is something to be avoided. For the sloth, however, it is a happy relationship.
Sloth hair is long, rough, and grooved in such a way as to encourage the presence of bacteria and algae. The algae gives sloths a terrific disguise by turning them green, which makes them harder to spot against the green leaves in which they live. One of the first gifts that mother sloths give their babies is the algae that will hide them from predators. So close is this relationship that the most common type of algae found on sloths, Trichophilus welckeri, is found nowhere else in nature.
With an algal bloom on their back, spotting a sloth is like trying to find a needle in a haystack . . . when the needle is hidden inside a piece of hay.