Class: Mammalia (Mammals)
length: 4.6 to 6 inches (12 to 15 centimeters)
Tail length: 6.8 to 9 inches (17 to 23 centimeters)
Weight: 3 to 5 ounces (85 to 140 grams)
Life span: up to 12 years in the wild, up to 18 years in zoos
Gestation: 4.5 months
Number of young at birth: 1 to 4, but usually 2
Weight at birth: 0.5 to 0.9 ounces (14 to 27 grams)
Age of maturity: 2 years
Conservation status: lower risk
• The word "marmoset” comes from the French word marmouset, meaning “shrimp” or “dwarf.”
• The pygmy marmoset is the smallest monkey but not the smallest primate—that's the mouse lemur.
• The pygmy marmoset's claw-like nails are called tegulae. The flat nails that other primates have are called ungulae.
Mammals: Pygmy Marmoset
High in the rain forest canopy of South America lives a tiny animal that dodges behind tree trunks and branches, alternately freezing and dashing, just like a squirrel. It also has brown fur and a long tail like a squirrel—but it's really a pygmy marmoset, the world's smallest monkey! Marmosets and their cousins, the tamarins, are some of the tiniest primates around, but pygmy marmosets are different enough to be classified apart from other marmoset species.
A full-grown pygmy marmoset could easily sit in an adult human's hand and it weighs about as much as a stick of butter. But there is nothing tiny about a pygmy marmoset's tail: it's longer than its body! The tail is not prehensile, but it helps the little monkey keep its balance as it gallops through the treetops.
Being tiny can be dangerous
Because they are so small, pygmy marmosets can become prey for many types of animals: cats, harpy eagles and hawks, and snakes. That is why they dash from one safe spot to the next. Their necks are very flexible and they can turn their heads backward to spot predators. Because they are so small, pygmy marmosets prefer living in dense rain forests where there are lots of hiding places among the plants.
Both male and female pygmy marmosets are orangish brown, with each hair having stripes of brown and black, called agouti coloring. This coloration gives them very good camouflage. A mane of hair covers the pygmy marmoset's ears. Most primates have flat nails on the ends of their fingers, along with opposable thumbs that allow them to grasp objects. However, except on the big toe, the nails of pygmy marmosets are folded over like claws to help them climb up and down tree trunks. They do not have opposable thumbs.
Tree sap is a big part of these tiny monkeys' diet.
The ability to climb is very important for pygmy marmosets because tree sap is their favorite food. They scamper up and down trees headfirst, clinging to the side of a tree trunk and gouging a hole in the bark with their sharp lower teeth, using an up-and-down sawing motion. When the sap puddles up in the hole, they lap it up with their tongues. Pygmy marmosets have certain trees they like within their 2.5-acre (1 hectare) territory; they can make up to 1,300 holes in each one! Sometimes they lie in wait for insects, especially butterflies, which are attracted to the sap holes. They also eat some nectar and fruit. At the San Diego Zoo, the pygmy marmosets are fed yams, carrots, leaf eater biscuits, bananas, apples, grapes, crickets, and mealworms.
Small monkey, big family
Pygmy marmosets travel in groups, called troops, of up to nine monkeys, with an average of five members. Usually the troop is made up of a breeding pair, their babies, and any of their adult children. The parents stay together for life. Living in a group is very useful for pygmy marmosets: there are more pairs of eyes to spot predators, and everyone helps take care of the little ones. For added safety, the troop spends the night among thick vines or in a tree hole.
Really tiny babies
A mother marmoset's gestation period is about 4.5 months and she gives birth every 5 to 7 months. She almost always has two babies, but in zoos, pygmy marmosets have had three or even four babies in one litter. Each newborn is about the size of a human thumb! The father helps deliver the babies, cleans them up, and then takes over their care. He carries the newborns piggyback style for the first two weeks, bringing them back to the mother to nurse. When they are a bit older, they hide while the rest of their family looks for food until they are strong enough to travel with the group. Usually the young marmosets are weaned and can follow the troop by three months of age. It takes them about two years before they are as large as the adults. They may leave the troop at this point to start a family of their own, or they may stay to help raise the newest babies. Usually neighboring troops of pygmy marmosets have territories nearby, marked by scent. This signals troops to leave each other alone.
A far-reaching alarm call lets the rest of the troop know if danger is near.
Pygmy marmosets communicate with each other by chattering and trilling in high-pitched voices—their own pygmy marmoset song! They also make faces to express emotions like contentment, surprise, or fear: they move their lips, eyelids, ears, and the hair around their faces. We humans do that, too! These mini monkeys also groom one another, and they are fussy about keeping their fur in good shape.
Not a cute pet
Like nearly every other primate species, pygmy marmosets are threatened by loss of habitat and fragmentation, from building roads through forests to clearing land for agriculture. They are also heavily collected for the pet trade, even though monkeys do not make good pets. Fortunately, the United States has banned their import and most South American countries don't allow primate exports anymore. However, pygmy marmosets are still kept as pets in South America.
If the current rate of habitat destruction can be slowed, these tiny monkeys will have a big chance at long-term survival in their forest home.