Facts About Monkeys

Monkeys are primates, a group characterized by opposable thumbs, forward-facing eyes, and complex brains; monkeys are split into two broad groups, Old World monkeys and New World monkeys.

Monkeys vary enormously in size, from the tiny pygmy marmoset to the much larger mandrill.

Monkeys are highly social, living in groups called troops that can range from a handful of individuals to several hundred, with a clear social hierarchy inside each group.

Monkeys are intelligent problem-solvers that have been observed using tools in the wild, such as sticks to probe for insects or stones to crack open nuts.

Monkeys are omnivores, and their diets vary by species: howler monkeys mostly eat leaves and fruit, while macaques eat a broader mix that includes insects, eggs, and small animals.

Many New World monkeys, such as spider monkeys, have a prehensile tail strong enough to grip branches and support their body weight; most Old World monkeys, including mandrills, lack this trait.

Many monkey species are endangered due to habitat loss, hunting, and the illegal pet trade.

Capuchin monkeys are skilled tool users, known for cracking open nuts by pounding them with stones.

Squirrel monkeys have the largest brain-to-body mass ratio of any primate, even proportionally larger than that of humans.

Howler monkeys are among the loudest land animals in the world; their calls can carry roughly 3 miles through dense forest.

Spider monkeys use their prehensile tail as a functional fifth limb, capable of supporting their entire body weight and even grasping small objects.

Mandrills are considered the most colorful primates, with vivid blue and red skin on their faces and rumps.

Rhesus macaques were among the earliest animals sent into space by the United States; a rhesus macaque named Sam flew a Mercury capsule test flight in December 1959, though the first primate in space was a rhesus macaque named Albert II in 1949.

Proboscis monkeys have the longest nose of any primate; in males it can grow to roughly 7 inches long and is thought to help attract mates and amplify their calls.

Golden lion tamarins are among the most endangered monkeys, living almost entirely within Brazil's Atlantic Forest; decades of conservation work have helped their wild population recover to roughly 2,500-3,700 individuals.

Japanese macaques, or snow monkeys, live farther north than any other non-human primate and are famous for warming themselves in natural hot springs during winter.

Geladas are unusual among primates for spending most of their time on the ground; they are the only primarily grass-grazing monkey and are known for the reddish 'bleeding heart' patch on their chest.

Tarsiers have the largest eyes relative to body size of any mammal, with each eyeball roughly the size of their brain.

Pygmy marmosets are the world's smallest monkeys, small enough to fit in a human hand, and feed partly by gnawing holes in tree bark to drink the sap.