A finger monkey is the nickname for the pygmy marmoset, the smallest monkey in the world. An adult weighs 85 to 140 grams, as much as a bar of chocolate. Pygmy marmosets live in the western Amazon rainforest and feed mainly on tree gum. Scientists now recognise two species, and both were listed as Vulnerable in 2025.
Finger monkey quick facts
- An adult pygmy marmoset weighs about the same as a 100 gram bar of chocolate.
- A group of pygmy marmosets can gnaw about 1,300 holes in a single tree to get at its gum.
- Pygmy marmosets are now counted as two species, split by the Napo and Amazon rivers about 2.5 million years ago.
- Some pygmy marmoset calls are so high-pitched that people cannot hear them.
- Since 6 April 2026, keeping any monkey in England without a council licence has been against the law.
Why it is called a finger monkey
Finger monkey is a nickname. The animal’s real name is the pygmy marmoset, and it is the smallest monkey in the world. People call it a finger monkey because a grown one is small enough to cling to an adult’s finger. Some people call it a pocket monkey, too.
Pygmy marmosets are New World monkeys. That means their family comes from Central and South America, like spider monkeys, howler monkeys and squirrel monkeys. Their closest relatives are the other marmosets and the tamarins, which are small tree-climbing monkeys too.
The nickname sounds sweet, but being so small and cute has a downside. San Diego Zoo Wildlife Alliance says the pet trade is the main threat these monkeys face. It blames their tiny size and appealing faces.
How small a pygmy marmoset really is
An adult pygmy marmoset weighs 85 to 140 grams (3 to 5 ounces), according to San Diego Zoo Wildlife Alliance. That is about as heavy as a 100 gram bar of chocolate. Its head and body together measure just 12 to 16 cm (about 5 to 6 inches).
The tail is the longest part. It measures 17 to 23 cm (about 7 to 9 inches), so it is longer than the rest of the animal. The fur is a speckled mix of brown, grey and gold, with faint dark bands along the tail.
| Measurement | Pygmy marmoset | Something you can picture |
|---|---|---|
| Adult weight | 85 to 140 g (3 to 5 oz) | a 100 g bar of chocolate |
| Head and body | 12 to 16 cm (5 to 6 in) | shorter than a new pencil |
| Tail | 17 to 23 cm (7 to 9 in) | about as long as a banana |
| Newborn baby | about 16 g (just over half an ounce) | lighter than an AA battery |
| Family home range | often under 0.2 hectares (half an acre) | less than a third of a football pitch |
A newborn is tinier still. Animal Diversity Web, a project of the University of Michigan, gives a birth weight of about 16 grams. That is less than a single AA battery weighs.
Being this small has costs. A tiny body loses heat quickly, and it makes the marmoset a meal for many hunters. It also has advantages. A pygmy marmoset can run along twigs far too thin to hold a bigger monkey.
One species or two?
For a long time, scientists said there was just one kind of pygmy marmoset. Its scientific name was Cebuella pygmaea. Older books split it into two subspecies, an eastern one and a western one. A subspecies is a group within a species that looks a little different and lives in its own area.
That has changed. In 2018, a team of scientists led by Jean Boubli compared the DNA of pygmy marmosets from across the Amazon. They found two groups that had been separated for more than two million years. That is long enough for them to count as two different species.
There was a snag. The name pygmaea belongs to one particular marmoset, collected by the naturalist Johann Baptist von Spix and described in 1823. Nobody was sure which riverbank his specimen came from. So nobody knew which of the two species should keep the old name.
In 2021, the team tested DNA from Spix’s 200-year-old specimen. It matched the marmosets living north of the river. So the northern species kept the name Cebuella pygmaea, and the southern species became Cebuella niveiventris. The scientists dated the split between them to about 2.5 million years ago.
| Northern pygmy marmoset | Eastern pygmy marmoset | |
|---|---|---|
| Scientific name | Cebuella pygmaea | Cebuella niveiventris |
| Where it lives | north of the Napo and Solimões-Amazon rivers | south of the Napo and Solimões-Amazon rivers |
| Countries | Brazil, Colombia, Ecuador, Peru | Bolivia, Brazil, Ecuador, Peru |
| IUCN Red List status (2025) | Vulnerable | Vulnerable |
The names can be confusing. The IUCN Red List now calls Cebuella pygmaea the northern pygmy marmoset and Cebuella niveiventris the eastern pygmy marmoset. Many zoos and websites still use the old western and eastern subspecies labels, and some still list only one species. For a school project, it is fair to write that scientists now recognise two species, and that the change is recent.
Where pygmy marmosets live in the Amazon
Pygmy marmosets live in the western part of the Amazon rainforest. Between them, the two species are found in Brazil, Colombia, Ecuador, Peru and Bolivia. Animal Diversity Web says they do best in forest along the edges of rivers, at low heights above sea level.
Rivers matter to them in two ways. The forest along a riverbank has the kinds of trees they feed from. Wide rivers also act as barriers that small monkeys cannot cross. That is why the two species ended up on opposite banks of the Napo and the Amazon River.
Inside the forest, pygmy marmosets stay in the understorey. That is the layer of small trees and vines between the forest floor and the tall canopy. Animal Diversity Web says they avoid both the ground and heights above about 18 metres (60 feet).
A family group does not need much room. San Diego Zoo Wildlife Alliance says its home range is often less than half an acre, about 0.2 hectares. The same riverbanks are home to capybaras, while pink river dolphins swim in the water below. You can meet more of their neighbours in our guide to the animals of the Amazon rainforest.
A diet of tree gum and sap
Most monkeys eat fruit and leaves. Pygmy marmosets mainly eat gum, the sticky liquid that oozes out of a tree when its bark is damaged. Scientists call animals that live like this gum-feeders.
To get the gum flowing, a marmoset bites into the bark with its long, sharp lower front teeth. Animal Diversity Web says these teeth let it drill an almost perfectly round hole. Gum and sap slowly seep into the hole. Later, the marmoset comes back to lick them up.
The holes soon add up. San Diego Zoo Wildlife Alliance says pygmy marmosets can gouge about 1,300 holes in a single tree. That is a lot of chewing. Picture a tree trunk dotted with tiny round scars, each one a marmoset’s food store.
Gum is not their only food. They also catch insects, especially butterflies that are drawn to the sweet sap. They eat some nectar and fruit, and now and then a spider or a small lizard. In zoos, keepers feed them fruit, vegetables, insects such as crickets and mealworms, and a special food made for monkeys.
Family life and twins
Pygmy marmosets live in small family groups called troops. San Diego Zoo Wildlife Alliance says a troop can have up to nine members, with an average of five. Most troops are a breeding pair and their young of different ages.
The mother and father usually stay together for life. The mother is pregnant for about four and a half months. She almost always gives birth to twins, and she can have a new pair every five to seven months.
That is a lot of babies for such a small mother. Two newborns of about 16 grams each weigh roughly a quarter as much as she does. So the father carries the newborns on his back from the start. He is the main babysitter. Animal Diversity Web says the father and the older brothers and sisters take on more and more of the carrying as the babies grow.
The mother still feeds the twins her milk. They are weaned, which means they stop drinking milk, at about three months old. Young males are ready to breed at about 638 days old and young females at about 684 days, a little under two years.
Trills, whistles and calls too high to hear
Pygmy marmosets call to each other all day long. Their voices are very high-pitched. San Diego Zoo Wildlife Alliance says some of their calls are too high for people to hear at all.
Animal Diversity Web lists trills, which work as alarm calls and help a troop keep in touch. It also lists soft twittering, which shows one marmoset giving way to another. Some calls even reach the ultrasonic range. Ultrasonic means higher than the highest sound a human ear can pick up.
Different calls do different jobs. Smithsonian Magazine reported in 2025 that a brief, high alarm whistle can sound like a cricket or a bird. Choppy calls known as J-calls help a troop keep in touch when its members are spread out.
Babies are noisy, too. The same report describes young pygmy marmosets babbling, stringing sounds together a little like a human baby does. Marmosets also send messages without sound, using body postures and scent marks.
Predators and staying safe
Being tiny makes a pygmy marmoset easy prey. Animal Diversity Web lists three main groups of predators: birds of prey, small wild cats and snakes that climb trees.
Each hunts in its own way. A hawk can snatch a marmoset from a branch. A small cat can climb after it. A snake can lie still and hidden near a feeding tree, waiting for the troop to come back to its holes.
The marmosets’ best defence is teamwork. When one spots danger, it gives an alarm trill, and the rest of the troop can dive for cover. Their small size helps here, because they can slip behind a branch or into thick leaves where a larger animal cannot follow.
Lifespan in the wild and in zoos
A wild pygmy marmoset can live for up to about 12 years, according to San Diego Zoo Wildlife Alliance. In zoos, with regular food, vet care and no predators, they can reach about 18 years. Zoo life is much safer.
Animal Diversity Web gives similar figures. It says wild pygmy marmosets live for 11 to 12 years, and that one in captivity reached 18.6 years.
Disease is a danger as well. A scientist interviewed by Smithsonian Magazine named yellow fever and herpes among the illnesses known to kill pygmy marmosets. Some of these diseases can pass from people to monkeys.
Why pygmy marmosets are now Vulnerable
Pygmy marmosets used to be listed as Least Concern, the lowest level of worry. Many fact pages still say so. That is out of date.
In the IUCN Red List assessments published in 2025, both species are listed as Vulnerable. The IUCN is the world conservation body that keeps the Red List of threatened animals and plants. Vulnerable means a species faces a high risk of dying out in the wild. For both species, the IUCN says numbers are going down.
The main problem is the loss of their forest. For the northern species, the IUCN lists new towns, tree plantations and mining. For the eastern species, it lists farming. Both species are also hunted and trapped.
Losses can happen fast. The scientist Stella de la Torre studied seven pygmy marmoset groups in Ecuador in 2012. When she went back in 2022, Smithsonian Magazine reported, she found only one.
There is some protection. Pygmy marmosets are covered by CITES, the international agreement that controls trade in wild animals. The IUCN also records that both species live in at least one protected area.
Why experts say they should not be pets
Videos of finger monkeys can make them look like living toys. They are not toys. Animal welfare experts say they are wild animals, with needs that no ordinary home can meet. The RSPCA, a UK animal welfare charity, says primates are intelligent, social wild animals with complicated needs.
- They need their family. The RSPCA says keeping a primate alone is inhumane, and that human company is no replacement for other primates. A wild pygmy marmoset lives in a troop of about five.
- They need the right food and light. The RSPCA says pet primates often get metabolic bone disease, the illness called rickets in people. It comes from the wrong diet and too little ultraviolet light, and it leaves bones weak and bent.
- They need warmth and room to climb. Pygmy marmosets are tropical animals that spend their whole lives in trees.
- They can bite. The RSPCA says pet primates can become aggressive as they grow up, and some have bitten and attacked their owners.
- Diseases can pass both ways. The US Centers for Disease Control and Prevention warns that primates can carry diseases that spread to people. People can also give illnesses to monkeys.
The trade also harms wild marmosets. Smithsonian Magazine reports that exporting pygmy marmosets from South America is against the law, yet they are still prized as pets. Many that are taken from the wild die in captivity.
What the law says in England and the United States
In England, the law changed on 6 April 2026. Since that date, nobody may keep a monkey or any other primate without a primate licence from their local council. That includes people who already had a primate before the change. The only exceptions are licensed zoos and licensed science laboratories.
The rules are called the Animal Welfare (Primate Licences) (England) Regulations 2024. A council must inspect the home before it grants a licence, and a licence lasts for three years at most. The government’s own explanation of the law says the aim was to make it illegal to keep primates as pets. Keepers must meet welfare standards close to those of a licensed zoo.
Those standards are strict. The licence conditions published on GOV.UK include:
- Primates must live in suitable social groups, not on their own.
- Every primate must be fitted with a microchip.
- Keepers must register with a named vet and keep detailed health records.
- Homes must have indoor and outdoor areas, things to climb, and the right warmth and humidity.
- Breeding is allowed only under a vet’s supervision, with a written plan.
Keeping a primate without a licence, or breaking its conditions, is a criminal offence. Before the law was made, the government estimated that between 1,000 and 5,000 primates were being kept as pets in England.
These rules cover England only. Scotland, Wales and Northern Ireland make their own animal welfare laws, so the rules there can be different.
In the United States, laws on keeping monkeys differ from state to state. National rules apply to bringing them into the country. The CDC says the import of primates has been restricted since 1975. It also says that bringing one into the United States to keep as a pet is illegal.
The real cost of a pet monkey
Lots of people search online for what a finger monkey costs. This guide does not give prices, because buying one keeps a harmful trade going. The costs that matter are different ones.
A pygmy marmoset would need at least one marmoset companion and a heated indoor and outdoor enclosure. It would also need special food and a vet who knows about primates. In England, it would also need a licence and council inspections. It could live for up to 18 years, which is longer than most children live at home. That is a long promise.
If you love pygmy marmosets, the best place to see them is a good zoo. There they live in family groups, with keepers and vets who know what they need.
Three things people get wrong
1. “There is only one kind of pygmy marmoset.” Scientists now recognise two species, the northern and the eastern pygmy marmoset, separated by the Napo and Amazon rivers. The names were settled in 2021, so many older pages still describe just one.
2. “Pygmy marmosets are not in danger.” Many fact pages still give their status as Least Concern. In the IUCN Red List assessments published in 2025, both species are Vulnerable, and their numbers are falling. The picture has changed.
3. “A finger monkey is fine as a pet if it is small and legal.” Size does not make a wild animal easy to care for. Experts such as the RSPCA say primates should not be pets. Since 6 April 2026, anyone in England needs a licence with zoo-like standards to keep one.
Did you know? Newborn twin pygmy marmosets together weigh about a quarter as much as their mother. That is why the father, and later the older brothers and sisters, do most of the carrying.
Try it
Picture a pygmy marmoset. Draw a line 14 cm long for its head and body, then carry on for another 20 cm for its tail. Next, hold a 100 gram bar of chocolate or a small apple in one hand. That is about how heavy an adult is. Now compare the size of its body with the length of its tail.
Knowledge check
Why do pygmy marmosets gnaw holes in tree bark?
Show answer
To make the tree ooze gum and sap, which they come back to lick up. Tree gum is their main food.
What has anyone keeping a monkey in England needed since 6 April 2026?
Show answer
A primate licence from their local council, granted only after the council has inspected where the animal lives.
Frequently asked questions
What is a finger monkey?
Finger monkey is a nickname for the pygmy marmoset, the smallest monkey in the world. Pygmy marmosets live in the western Amazon rainforest of South America, and an adult is small enough to cling to a person’s finger.
How big is a finger monkey?
An adult pygmy marmoset weighs 85 to 140 grams (3 to 5 ounces), about as much as a 100 gram bar of chocolate. Its head and body measure 12 to 16 cm (5 to 6 inches), and its tail adds another 17 to 23 cm.
How long do finger monkeys live?
Pygmy marmosets live for up to about 12 years in the wild, according to San Diego Zoo Wildlife Alliance. In zoos, with regular food, vet care and no predators, they can live to about 18 years.
Can you have a finger monkey as a pet?
Animal welfare experts, including the RSPCA, say pygmy marmosets should not be kept as pets, because a home cannot meet their needs. In England, anyone keeping a primate has needed a council licence since 6 April 2026. In the United States, the rules vary from state to state.
Where do finger monkeys live?
Pygmy marmosets live in the western Amazon rainforest, in Brazil, Colombia, Ecuador, Peru and Bolivia. They prefer forest beside rivers and stay in the understorey, the layer between the forest floor and the tall treetops.
What do finger monkeys eat?
Pygmy marmosets mainly eat tree gum and sap. They gnaw small round holes in bark with their sharp lower teeth, then lick up the gum that seeps out. Insects, nectar and fruit make up the rest of their food.
Are pygmy marmosets endangered?
Both species of pygmy marmoset were listed as Vulnerable on the IUCN Red List in 2025, one step below Endangered. Their numbers are falling because of forest loss, hunting and trapping.
Sources
- San Diego Zoo Wildlife Alliance: pygmy marmoset — size, weight and tail length, the 1,300 gum holes, troop size, twins, fathers carrying babies, high-pitched calls, home range, lifespan in the wild and in zoos, and the pet trade
- Animal Diversity Web, University of Michigan: pygmy marmoset — birth weight, understorey habitat, drilling teeth, diet, age at first breeding, infant carrying, trills and ultrasonic calls, predators, lifespan and CITES
- Boubli and others, Zoological Research (2021): ancient DNA of the pygmy marmoset type specimen — the split into two species, the 2018 DNA study, Spix’s 1823 specimen, the rivers that separate the species and the 2.54-million-year split
- IUCN Red List (2025): northern pygmy marmoset, Cebuella pygmaea — Vulnerable status, falling numbers, countries and threats; the eastern pygmy marmoset’s 2025 assessment gives the same category
- legislation.gov.uk: The Animal Welfare (Primate Licences) (England) Regulations 2024 — the licence needed from 6 April 2026, the zoo and laboratory exceptions, three-year licences, inspections, social groups and microchipping, and the explanatory memorandum’s estimate of 1,000 to 5,000 pet primates
- RSPCA: keeping primates as pets — why primates should not be pets: their social needs, diet, metabolic bone disease and aggression
