Females tend to be a little larger and heavier than males. They have very long arms and legs and even just the tip of their tail can support the weight of their entire body.
Spider monkeys have no thumbs or it is reduced to a nub.
Several subspecies have flesh-colored rings around the eyes and their hands and feet are usually black. Infants have a pink face and ears. They may have a white patched triangle on their forehead and some have white sideburns. Their tail is very thick at the base. They are non-seasonal breeders and have a gestation period of 225 to 230 days.