Deep in the humid Amazon rainforests, you will find tiny animals called the finger monkey. We also know them as the pygmy marmoset or pocket monkey. These little creatures are the smallest species of monkeys in the world and are so tiny that they can fit in the palm of your hand. But that is not the only fascinating thing about these creatures.
Read on as we uncover some interesting facts about finger monkeys.
You might be asking, "What is a finger monkey?" Well, the finger monkey is the smallest monkey and is known as one of the smallest primates in the world6. While these creatures are the smallest monkeys, they are not the world's smallest primates. The smallest primate in the world is the Mouse Lemur7 which measures around 2.25 to 4.75 inches and weighs 1 to 4 ounces.
We call these animals finger monkeys because these tiny animals can wrap around your finger. For example, a newborn pygmy marmoset monkey is as little as a human thumb.
The pygmy marmoset has orange-brown fur with black and brown stripes. This dark fur helps them hide in trees and away from predators. It has small eyes, a nose, and ears.
"How big do finger monkeys get?" - These creatures only grow between 4.6 to 6 inches from head to body and weigh around 100 grams. However, these creatures have tails that are longer than their entire body and measure about 6.8 to 9 inches. In addition, their tails are not prehensile, so they can’t use them to grip tree branches or eat fruits3.
Finger monkeys are called New World monkeys. All monkeys fall under the Old World or New World primates. Both categories have notable differences in size, diet, breeding season, reproductive cycles, habitats, etc.
Pygmy marmosets are native to South America, where we find the majority of New World monkeys. These creatures also have broad flat noses and other notable features that fit the characteristics of New World monkeys.
Scientifically, pygmy marmosets are more primitive than other monkey species. For example, they don’t have opposable thumbs and prehensile tails.
The scientific name for the finger monkey is Cebuella pygmaea, and they belong to the Callitrichidae family. Finger monkeys or pygmy marmosets have two main species: the Western pygmy marmoset (Cebuella pygmaea pygmaea) and the Eastern pygmy marmoset (Cebuella pygmaea niveiventris).
These two finger monkey species have slight differences in color, geographic range, and morphology. Both species live in the Amazon region of Brazil, Colombia, Ecuador, Peru, and Northern Bolivia. We can find the Western pygmy marmoset in the North and West of the Amazon Basin. On the other hand, the Eastern pygmy marmoset lives in the East of the Amazon Basin.
"Where do finger monkeys live?" - Like most monkeys, pygmy marmosets live in trees. However, these creatures prefer the tropical rainforest climate. You will find finger monkeys living in forests where trees grow close to each other, which shields them from predators and helps them jump to different tree branches.
Thanks to their brown/orange fur, they can camouflage themselves among tree trunks and dark branches. Pygmy marmosets prefer to stay in the lower tree cover, where they are safe and can more easily access food sources. You can also find these small monkeys in swamps, streams, and tree-lined rivers.
Just like other monkeys, a group of monkeys is called a troop. Most finger monkeys live in groups of 2 to 6 individuals.
The troop typically consists of a single male, female, and children. However, there may be other adults in the group. The females can get pregnant at any time of the year, so there isn’t an exact time pygmy marmosets decide to leave the troop. However, male and female juveniles eventually break off, and an adult pair births and establish its own troop after some time.
Pygmy marmosets are different from other monkeys when it comes to their anatomy. Most monkeys typically have flat nails, but the pygmy marmoset has claws on its digits. They use these claws to move around trees and better grip on tree branches. They also lack opposable thumbs like other monkeys. These features help them adapt to their arboreal lifestyle.
The pygmy marmoset's diet consists of a variety of food. They are omnivores. However, these small monkeys prefer tree sap, tree resin, tree gum, and any fluid that comes from trees. Because of their limited home ranges, the pygmy marmoset cannot rely solely on fruits and has evolved to feed on tree sap.
Thanks to their sharp teeth, these small monkeys can easily dig holes into the bark of trees to get tree sap. Aside from tree sap, the pygmy marmoset diet includes flowers, fruits, insects, small lizards, spiders, and other small reptiles.
Finger monkeys or pocket monkeys are highly social animals. As we mentioned earlier, the finger monkey lives in a group of 2 to 6 individuals, which make up a troop. These social creatures bond by grooming each other, sleeping together, and engaging in other social activities. They make roosts at night and begin their activities in the morning. Typically, pygmy marmosets will start the day by enjoying some tree gum from a hole and break out in groups to play, groom each other, and source more food.
Pygmy marmosets have a complex way of communicating with one another1. A finger monkey can make a bird-like call; over long distances, finger monkeys call out in lower frequencies to locate other finger monkeys. The female finger monkey doesn’t show any outward signs of ovulation. Instead, they use scent marks to let the adult males know they are ready to mate.
Pygmy marmosets can also alter their calls to fit their social environment and even imitate their group members' calls.
Typically, finger monkeys are monogamous, which means they stay with one mate for a lifetime. Dominant males will show aggression to other male finger monkeys who try to mate with the female finger monkey.
However, the females may have numerous male mates in a group with multiple male finger monkeys. This can be pretty rare due to limited habitat.
The gestation period of a pygmy marmoset is around 4.5 months. The breeding female pygmy marmoset will then produce twins. Sometimes the pygmy marmosets may give birth to one or three babies. However, twins are more common.
A baby pygmy marmoset weighs around 4 ounces, around the size of a human thumb. At three months old, baby pygmy marmosets eat insects and tree sap.
The pygmy marmoset is one of the smallest primates, which comes with disadvantages. These animals have a slow metabolism rate which may be because of the kind of food they eat2.
Because of their slow metabolism, they struggle not to lose heat from their bodies. In other words, the pygmy marmoset works to stay warm, making them more vulnerable to climate change.
Pygmy marmosets are arboreal animals and have developed some adaptive features. One of them is the ability to turn their heads 180 degrees backward. Yes, pygmy marmosets can turn their heads backward in the opposite direction, thanks to extra flexible necks. This helps them get a 360-degree view of the surrounding areas while looking for predators on the tree branch.
When baby finger monkeys are born, the father is the primary caretaker. The babies ride on the back of the father, and when it's time for them to feed, the father carries the babies to their mother to nurse them.
Pygmy marmosets attain sexual maturity between 12 to 16 months. When a young pygmy marmoset is one and a half or two years old, it becomes a fully grown finger monkey and may leave the group to start its own family. However, there are some cases where they stay in the group to help raise other babies. A male and a female in a troop breed while other group members care for the young.
The average lifespan of a finger monkey is around 11 to 12 years. However, pygmy marmoset predators may affect their lifespan.
Interestingly both parents are not the only group members that raise their young. Other members of the group also help raise the younger pygmy marmosets. These individuals may even delay starting their own families. Instead, they stay to watch out for predators and scout for food for the younger finger monkeys. This is great for parents, so they are only sometimes occupied with caring for their young.
While pygmy marmosets may be tiny creatures, you don’t want to underestimate their jumping abilities. As we mentioned earlier, pygmy marmosets are arboreal and live in rainforests where they are faced with threats from natural predators like small wildcats, birds, and snakes like the pit viper, which can climb tall trees.
To adapt to their environment and avoid predators, finger monkeys can also dash and leap as high as 15 feet into the air between branches. If pygmy marmosets spot a predator, they also call out their troop. A large troop may occasionally work together to ward off a predator.
A finger monkey is one of the smallest primates in the world. Because of this reputation, people love to take in finger monkeys as exotic pets. So apart from their natural habitat, you will likely find finger monkeys in zoos, national parks, and pet stores.
Finger monkeys can be good pets depending on how well you care for them. They require great care, so pet owners must devote considerable time to feeding, bathing, and socializing with them.
Because they are wild animals, the pygmy marmoset may act in unpredictable ways if not correctly taken care of. Also, because the pygmy marmoset or pocket monkey is a social animal, they should not be kept alone. You will need to keep at least one companion with them. It is also essential to look out for local laws before getting a finger monkey as a pet.
However, finger monkeys cost a decent amount of money, and aren't a light undertaking.
One of the most interesting facts about the finger monkey is that just like human infants, the baby pygmy marmoset babbles at the initial stage to hone its communication skills5. Vocalization is essential for their survival, and just like humans, their babies have to learn how to talk.
During the holiday season in 2017, WowWee released a line called Fingerlings. These were colorful robotic animal toys that you could wrap around your finger. The company drew its inspiration from the finger monkey. The toy didn’t only come in the form of monkeys; the company manufactured others to resemble unicorns, sloths, dragons, and so on.
One major threat to pygmy marmosets is the pet trade. The pet trade involves selling exotic animals around the world. These animals are taken away from their natural habitat and sold to make profits. Some of these practices are legal, but many of them are illegal. As a result, the pygmy marmosets' reputation as the smallest monkey in the world has sadly led to them being hunted down.
Generally, primates are challenging to take care of, and many suffer from inadequate support. The pygmy marmoset is very sensitive, and any interference with their natural order can cause changes in their behavior. Pygmy marmosets may become less sociable, nervous, or even aggressive. Ultimately, this can affect their development.
Sadly, the pet trade is not their only threat. Habitat loss is another severe threat for the pygmy marmoset4. The logging, mining, and deforestation of the Amazon rainforest in South America have also displaced many finger monkeys, making them more vulnerable to predation and starvation. As a result, these creatures lose their tree covers and scatter throughout the continent.
Sadly, the pygmy marmoset and other monkeys face the sad fate of falling off trees. Arboreal life requires a lot of skills; this can be challenging for infants trying to learn.
Unfortunately, one of the significant causes of death in monkeys is falling off trees. Many other primates have opposable thumbs, which can help maintain balance. However, the pygmy marmoset doesn’t have this adaptation, making it more vulnerable to falling from trees.
Studies show that around 67% of the pygmy marmoset population makes it to adulthood.
Pygmy marmosets are tiny, colorful, and some of the most fascinating monkeys in the world. What’s even more unique about these creatures is that they are so small you could wrap them around your finger. In addition, they have sophisticated communication and adaptive skills, which help them adapt to arboreal life and protect them from predators.
Sadly, these tiny monkeys are vulnerable due to the pet trade and habitat loss.
Snowdon, C. T., & Hodun, A. (1981). Acoustic adaptations in pygmy marmoset contact calls: locational cues vary with distances between conspecifics. Behavioral Ecology and Sociobiology, 295-300.
Genoud M, Martin RD, Glaser D. Rate of metabolism in the smallest simian primate, the pygmy marmoset (Cebuella pygmaea). Am J Primatol. 1997;41(3):229-45. doi: 10.1002/(SICI)1098-2345(1997)41:3<229::AID-AJP5>3.0.CO;2-Z. PMID: 9057967.
Youlatos, D. (2009). Locomotion, postures, and habitat use by pygmy marmosets (Cebuella pygmaea). In The smallest anthropoids (pp. 279-297). Springer, Boston, MA.
de la Torre, S., Snowdon, C. T., & Bejarano, M. (2000). Effects of human activities on wild pygmy marmosets in Ecuadorian Amazonia. Biological Conservation, 94(2), 153-163.
Snowdon, C., & Elowson, A. M. (2001). 'Babbling'in pygmy marmosets: Development after infancy. Behaviour, 138(10), 1235-1248.
Soini P. Ecology and population dynamics of the pygmy marmoset, Cebuella pygmaea. Folia Primatol (Basel). 1982;39(1-2):1-21. doi: 10.1159/000156066. PMID: 6815036.
Atsalis, S. (2015). A natural history of the brown mouse lemur. Routledge.
Jen’s a passionate environmentalist and sustainability expert. With a science degree from Babcock University Jen loves applying her research skills to craft editorial that connects with our global changemaker and readership audiences centered around topics including zero waste, sustainability, climate change, and biodiversity.
Elsewhere Jen’s interests include the role that future technology and data have in helping us solve some of the planet’s biggest challenges.