Smallest Monkey Species: The Miniature Primates of the Rainforest

At the opposite end of the family from mandrills and baboons sits a group of primates small enough to sit in a cupped hand. The smallest monkey species weigh less than a smartphone, yet they hold territories, raise twins and defend themselves in one of the most competitive environments on Earth.

The Pygmy Marmoset: The Smallest Monkey in the World

The pygmy marmoset of the western Amazon is the smallest true monkey, with adults weighing roughly 100 to 140 grams and measuring around 12 to 16 centimetres in the body, plus a longer tail. It survives by gouging holes in tree bark with specialised lower incisors and returning to feed on the gum that seeps out, supplemented with insects drawn to the same sap. Groups are small, territorial and unusually quiet, communicating partly in calls at frequencies humans barely notice.

Other Featherweights

• Silvery and common marmosets – between 300 and 400 grams, the marmosets most often seen in human care. See our marmoset profiles.
• Pygmy and saddle-back tamarins – slightly larger cousins with the same twin-rearing strategy, profiled among our tamarin species.
• Talapoins – at roughly 700 to 1,300 grams these swamp-forest specialists are the smallest Old World monkeys, found in Gabon, Cameroon and Angola.
• Squirrel monkeys – around 600 to 1,100 grams, small enough to be agile yet social enough to live in troops of fifty or more.

How Being Small Changes Everything

Diet and metabolism

A small body loses heat quickly and cannot store much energy, so the smallest monkeys eat frequently and target concentrated foods: tree gum, ripe fruit, nectar and insects. That is why a marmoset diet looks nothing like a macaque diet, a point developed in what monkeys eat and the species feeding guide.

Predation risk

Everything from snakes and raptors to small cats will take a marmoset, so vigilance is constant and alarm calls are finely graded. Our guide to monkey predators explains the defensive toolkit, and how monkeys communicate covers the calls themselves.

Breeding strategy

Marmosets and tamarins routinely give birth to twins and rely on fathers and older siblings to carry them, a cooperative system unusual among primates. It is described in more depth in monkey reproduction and baby monkeys.

Small Does Not Mean Easy

Because they are little, the smallest monkeys are often assumed to be low-maintenance companions. The opposite is true. They need tall, densely furnished enclosures, a gum-and-protein diet that is difficult to source, warm and stable temperatures, and constant social stimulation. Read our enclosure guide, our advice on enrichment, and the legal position before making any decision.

Frequently Asked Questions

What is the smallest monkey in the world?

The pygmy marmoset of the western Amazon, weighing roughly 100 to 140 grams with a body length of 12 to 16 centimetres.

Is the mouse lemur smaller than the pygmy marmoset?

Yes, but mouse lemurs are not monkeys. Among true monkeys, the pygmy marmoset holds the record.

What is the smallest Old World monkey?

The talapoin of Gabon, Cameroon and Angola, at roughly 700 to 1,300 grams.

Do small monkeys make easier pets?

No. Small species are more fragile, need specialised gum-based diets, higher ambient temperatures and constant social company, which makes them harder to keep well rather than easier.

Related Reading

Compare the extremes in largest monkeys on Earth, place these species in context with types of monkeys, and see where they live in rainforest monkeys.