What Is a Monkey?

A monkey is a clever, mischievous and sometimes mysterious animal. They are mainly tree-dwellers (arboreal), and most species are active during the day. Monkeys are part of the order of mammals called primates, which also includes apes like chimpanzees and orangutans. However, monkeys have one key feature that apes do not: Every monkey has a tail—even if it is just a tiny nub. These special tails are ridged on the underside and can grip branches like the fingertips of a human hand. They are known as prehensile, and they come in handy for holding on to branches when climbing or moving around on the ground.

Almost all monkeys are social animals that live together in groups. They communicate with facial expressions and body movements, as well as by making many different sounds. These sounds can range from barks and purrs to shrieks, yips and screams. Some monkeys even make deep howls. In addition, some kinds of monkeys groom each other to clean away dirt and parasites. They also groom as a way to express affection or to make peace with other troop members.

Monkeys are found in a wide variety of habitats, from tropical rainforests to savannas and rocky areas. Some, such as geladas and Japanese macaques, live in mountainous regions where it snows. Other species, such as baboons and mandrills, inhabit open grasslands or rocky hilltops.

The size of a monkey can vary greatly—from the pygmy marmoset to the largest baboon. Some, such as colobus and langurs, have chambered stomachs that help them digest leaves. Others, such as baboons and some mandrills, are able to chew meat—though they mainly eat fruits, seeds, roots, shoots, flowers, and insects. Monkeys have a varied relationship with humans—some are kept as pets, while others are used in scientific research or on space missions. In popular culture, monkeys often appear in films and TV shows. They are also featured in literary works, such as the book Journey to the West.