One of the largest of South American monkeys, black-handed spider monkeys (sometimes called Geoffroy’s spider monkeys) have yellow-gray fur with black or reddish sides. Their face is mostly black, except for the pink areas surrounding their mouth and eyes. Their underside is lighter yellowish or white, but they are black around their knees, hands, elbows, and feet. They have four fingers but no thumb, and they have a long, prehensile tail. The underside of the end of the tail is a hairless fleshy pad that looks and functions a lot like the palm of a hand. Male and female spider monkeys live together in groups according to food availability, up to 20 in fruit season.