What is the smallest monkey species in the Amazon rainforest?

The pygmy marmoset is the smallest monkey species found in the Amazon rainforest and is widely described as the world’s smallest true monkey. It belongs to the genus Cebuella and weighs only a little over 100 grams—roughly the weight of a small apple.

Pygmy marmosets live in the western Amazon Basin, including parts of Brazil, Colombia, Ecuador, Peru, and Bolivia. They are especially associated with evergreen forests and river-edge habitats, where their tiny size helps them move through thin branches and dense vegetation.

Their diet is unusual among monkeys: they are specialized gum-feeders. Using sharp lower incisors, they make small holes in tree bark and return to collect the flowing sap. They also eat insects, fruit, and other small foods when available.

The name can cause confusion because “pygmy marmoset” refers to two closely related species: the western pygmy marmoset and the eastern pygmy marmoset. Both were once treated as a single species, but they are now recognized separately. They typically live in family groups of two to nine animals and communicate with a complex range of calls and visual signals.