By Nicholas Wade
Spare a minute from your frenetically busy day to consider the quite different life of the three-toed sloth.
It’s true that the sloth, which lives in the jungles of Central and South America, would barely prevail in a race with a snail. But it’s not a sluggard because it’s lazy. Rather, it has carved out a remarkably ingenious mode of life in the treetops, but one that imposes certain constraints on its speed and energy level.
The sloth is not so much an animal as a walking ecosystem. This tightly fitting assemblage consists of a) the sloth, b) a species of moth that lives nowhere but in the sloth’s fleece and c) a dedicated species of algae that grows in special channels in the sloth’s grooved hairs. Groom a three-toed sloth and more than a hundred moths may fly out. When the sloth grooms itself, its fingers move so slowly that the moths have no difficulty keeping ahead of them.