Muriqui Monkey: Largest of the New World Monkeys

Brachyteles arachnoides

Imagine living in a community where no one competes for food, bickers over where to sleep, or vies for breeding privileges. In this peaceful community, everyone also has a close social bond, complete with a morning ritual of hugging. Now you’re probably picturing a group of people holding hands around a campfire, singing Kumbaya in tie-dyed shirts and thinking how absurd such a perfect scenario seems. Well, this is the lifestyle of Brazil’s muriqui monkeys, the largest of the New World monkeys.

Their common name is fitting since “muriqui” is the native Tupi word for “largest monkey.” Sometimes referred to as woolly spider monkeys, due to their close relations to both woolly monkeys and spider monkeys, there are two species of muriquis: northern (Brachyteles hypoxanthus) and southern (B. arachnoides).

Muriqui Physical Appearance

The alternate common name, woolly spider monkey, derives from their thick, woolly coats. Muriquis vary in color, a range of brown, black, gray, and yellowish. All but a patch under their prehensile tail (which is used to help grip branches) and their face is covered in fur. As muriquis age, their black face becomes more mottled. Males and females are similar in size, about 38-58cm long from the top of the head to the base of their tail, and they weigh between 4.5-9kg.

There are a couple differences between northern and southern populations. While the teeth of northern muriquis show no sexual dimorphism from males or females, the canines of male southern muriquis are much longer than those of the females. Also, while northern muriquis have a vestigial thumb, southern muriquis are completely missing this appendage. Over time, these monkeys evolved to no longer need a thumb due to their behavior of rapidly swinging and gripping branches. A thumb became unnecessary, probably hindering efficient locomotion.

Muriqui Habitat

Muriquis inhabit a very isolated region of Brazilian Atlantic coastal forest at altitudes between sea level and 1800m. The northern species ranges within the states of Espírito Santo, Bahia, and Minas Gerais. The southern species ranges in São Paulo, southern Minas Gerais, and southern Rio de Janeiro.

Their habitat consists of severely fragmented patches of primary and secondary semi-deciduous forest. Since the overall forest composition has been altered by human exploitation, muriquis have learned to adapt to surviving off diverse tree species. Temperatures in these habitats vary between 12-26˚C during the year, with an average of 1.2m of annual rainfall.

Muriqui Diet

Being primarily a folivorous monkey, or leaf eater, muriquis have evolved specialized teeth and digestive systems that can handle large quantities of a low-calorie diet. They are also frugivores, which means they will feed on fruits and berries as well. Buds, flowers, and bark are other items on the muriqui’s menu. The amounts of vegetation consumed differs between species and seasons, regulated by availability in their limited habitat.

“Hippie Monkey”: Make Peace Not War

In comparison to other primate species, muriquis may spend up to half of the day resting. Most the other half is dedicated to traveling throughout their 2-8km2  home range looking for food. Demonstrating cooperative behaviors while feeding, muriquis will often hug when passing by each other on a branch. Nicknamed the “hippie monkey,” muriquis constantly show affection to each other by maintaining physical contact, exchanging face-to-face embraces, and participating in group hugs. They are often seen as a tangle of fur and limbs, cuddled amongst the canopy. Awwwwww! Although they will loudly chase other monkey species away from their group, there is no pecking order among members while resources are shared. During rare instances of tension, a younger monkey will often solicit a hug from an elder to calm the situation.

Muriqui Reproduction

Muriquis are polygamous, with males spending much time together in tightly bonded social groups that show no aggression during breeding. Unlike many other primates, females invite a male to mate with, as opposed to being chased down and forced to submit. Around age 5-7 years, females will move into other groups before reaching sexual maturity at age 11. Males typically reach sexual maturity around 5-6 years. Gestation lasts 216 days before an offspring is born during the dry season of May to September. Young are then weaned between 18-30 months. The lifespan of muriquis is still unknown.

Muriqui Conservation Status

Listed as Critically Endangered on the IUCN Red List, there are less than 2,000 muriqui monkeys left in the wild.


Due to the rate of habitat destruction, there is an enormous impact on biodiversity as a whole. The status of primate species is an issue that arises from logging and clearing entire areas of natural forest. It is estimated that almost half of the world’s 634 primate species are under threat of extinction, and the majority of these are in tropical forests. The more human populations grow, the more resources are extracted from the forests, and the more primate habitat is degraded or destroyed. Many people may wonder why primates should be conserved. Ecologically, many primate species play a vital role in environmental interactions, such as seed dispersal to aid in the health of the forests. This allows them to be “keystone species.”


Reserves and national parks are a way to officially protect an area and its inhabitants. A problem that arises in South America, however, is that parks often only exist on paper. Many governments lack the funding to protect and enforce regulations in those reserves. Local people continue to live within the reserve boundaries. Conservation works best when a compromise with local people is met. To prevent people from losing their homes and way of life, it is best to educate the locals on methods of efficient forest resource sharing and how the protection of the forest ecosystem services is in people’s best interest.  Properly managed reserves contribute to financial benefits that are passed through the whole community, such as compensation to landowners who no longer use their forested land.

Environmental legislation and the increase of public awareness have dramatically improved in Brazil. However, many residents in the Amazon, along with many politicians, still have a “pro-development” attitude. Hearings to discuss development projects in the Amazon are often poorly attended and have little impact. It is imperative that conservation professionals work more closely with community members, politicians, social scientists, and economists to imbed environmental knowledge. Traditional environmental education leads to the thought that human behaviors can be changed through more understanding of certain issues. This, in turn, would lead toward a higher motivation for people to act more responsibly toward the environment.

Ongoing Research on the Muriqui

Research on northern muriquis has been conducted by Dr. Karen Strier and her colleagues in Brazil since 1982 at the RPPN Feliciano Miguel Abdala on Fazenda Montes Claros, a privately-owned ranch. This property has been protected by the owner and has been a significant source for learning about muriqui natural history.

Southern muriqui study sites are within Parque Estadual de Carlos Botelho and Fazenda Barreira Rico in the São Paulo state. In Carlos Botelho, the muriquis live in one of the largest undisturbed regions of Atlantic coastal rainforest where these monkeys are found. The study sites for northern muriquis include Reserva Biologica Augusto Ruschi in Espírito Santo and Fazenda Esmeralda in Minas Gerais.

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Written by Katey Duffey

Katey Duffey is a wildlife biologist who studies carnivore conservation. She has a M.A. in Zoology from Miami University. Her main interest is in mitigating human-carnivore conflicts.Her research includes snow leopard population surveys, snow leopard / herder interactions, and zoonoses in the mountains of western Mongolia. Projects have been in partnership with Mongolian Academy of Sciences, Irbis Mongolia, Green Initiative NGO, and Duquesne University.

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