A monkey is a primate of the Haplorrhini suborder and simian infraorder. It excludes apes, which share an ancestor with monkeys but belong to a different branch of the family tree and are more closely related to humans and chimpanzees (Pan troglodytes). Usually smaller than apes, most monkeys have tails that hang straight down rather than being prehensile, or capable of coiling around objects; some species are tailless. Monkeys are a diverse group, ranging in size from the tiny pygmy marmoset to the huge mandrill.
They are generally very agile climbers, and their long arms and legs enable them to grasp branches and other surfaces with ease. Most live in trees, but some, such as colobus monkeys, are at home on the ground and can even swim! Some have hind legs that are much longer than their forelimbs, allowing them to make incredible leaps.
Monkeys are highly social, and groups of monkeys, called troops, usually travel together during the day in search of food. They use vocalizations and facial expressions to communicate with each other, including barks, shrieks, grunts, clicks, clucks, squeaks, whoops, hoots, and wails. They may even give a “monkey yawn” when they are stressed or feeling threatened!
Monkeys are omnivorous, and their diets include leaves, fruit, flowers, seeds, and insects. Some, such as colobus monkeys, have specialized digestive tracts that help them digest leaves. They reproduce throughout the year, but most species bear young at times that best suit their survival.