(They also have thumbs but those are extremely short.) Their tree-to-tree locomotion, called brachiation, is how these swingers get around. The spider monkey’s tail is prehensile, which means ...

Unlike virtually every other primate, spider monkeys have no thumbs, which could snag on the branches. Instead, their four long fingers form a perfect hook to help them swing on branches.

Monkeys are different from apes. In case you’re wondering about the specifics, my editor, Genevieve Koski, points to a useful rule of thumb: Monkeys have tails; apes — like chimps, gorillas ...