Brachyteles arachnoides

Geographic Distribution and Habitat

Southern muriquis (Brachyteles arachnoides), or southern woolly spider monkeys, are endemic to the country of Brazil. They occupy fragments of submontane and montane evergreen tropical primary and secondary forests, 1,312–5,906 ft (400–1,800 m) above sea level, along the Atlantic coast within the states of southeastern Minas Gerais, northern São Paulo, southern Rio de Janeiro, and northeastern Paraná.

In Minas Gerais, the muriquis reside along the southern slopes of the Serra da Mantiqueira mountains. The Serra de Paranapiacaba mountain range in São Paulo is home to the species’ largest population, while a remnant population lives along São Paulo’s Piracicaba and Tiete River deltas. East of São Paulo, between Minas Gerais and Rio de Janeiro, the muriquis reside at the southern edge of the Paraíba do Sul River. The Reserva Ecologica de Guapiaçu (REGUA) is home to Rio de Janeiro’s largest population. In Paraná, the municipalities of Castro and Doutor Ulysses each host a small population.

Human development, a lack of contiguous forest, and natural barriers that include the Rio Grande, Rio Paraiba do Sul, and the Serra da Mantiqueira mountain range geographically separate southern muriquis from their sister species, northern muriquis (B. hypoxanthus), or northern woolly spider monkeys. The lack of physical contact with one another makes interbreeding between the species impossible, thereby creating two distinct populations.

Wildlife biologists who have studied both species posit that the differing forest composition of the two populations is testament to muriquis’ resiliency for surviving in diverse habitat. Habitat loss has gravely impacted the future of both species, however.

Southern Muriqui range, IUCN 2019

Size, Weight, and Lifespan

Muriquis are South America’s largest monkeys and are the two largest species of New World monkeys. When hanging from tree branches with their long arms outstretched, they give the illusion of being nearly five feet tall! Their true stature is a bit less. Nevertheless, muriquis possess a commanding physicality.

Southern muriquis edge out the northern species (northern muriquis) by being a little bit taller and little bit heavier.

Head-to-body length for adult males ranges from 1.81 to 2.6 ft (55–78 cm). A long, fully prehensile tail adds another 2.4–2.8 ft (74–84 cm), with an average tail length of 2.6 ft (79.1 cm). Southern muriqui males weigh between 21 and 33 lb (9.6–15 kg), with an average weight of 22.5 lb (10.2 kg).

Head-to-body length for adult females ranges from 1.5 to 2.1 ft (46–63 cm). A long, fully prehensile tail adds another 2.4–2.6 ft (74–80 cm). Southern muriqui females weigh between 18 and 24 lb (8–11 kg), with an average weight of 18.24 lb (8.5 kg).

Lifespan for the southern muriqui is conjectured to be 40 years old in the wild, based on the lifespan of the more extensively studied northern muriqui.

What Does It Mean?

The ability to produce live offspring. 

Prehensile tail: 
The tail of an animal that has adapted to be able to grasp or hold objects.   

Occurring or living in the same area; overlapping in distribution. 

Visit the Glossary for more definitions


These monkeys look like personable individuals with whom you’d like to hang out and have a nice chat—if you could hang from a high tree branch in a Brazilian forest. But you probably can’t . . . and you shouldn’t.

Both southern and northern muriquis are similar in appearance. Poofy, woolen coats cover their bodies, including their spindly limbs and pot bellies (accoutrements and physical attributes that may lend themselves to the species’ alternative name of woolly spider monkeys). Coat colors vary from gray to yellow-brown to a creamy, light toffee.

But the most obvious distinction between the two species is their hairless face. The facial skin of southern muriquis is entirely black, while the black facial skin of northern muriquis is mottled with splotches of pink pigments.

Another major distinction between the two species is the thumb, or lack thereof.  Nature has completely removed this apparatus from the southern muriqui’s physique and left a mere stub (known as a “vestigial” thumb) on the claw-like hand of the northern muriqui.

Southern muriquis may be thumbless, but they are equipped with impressive canine teeth, longer than those of northern muriquis. The canine teeth of southern muriqui males are considerably longer than those of the females, an example of canine sexual dimorphism.


Muriquis are total herbivores, eating mostly fruits and leaves (the southern species eats more fruits than leaves, while the northern species eats more leaves than fruits). A small amount of flowers, tree bark, buds, and seeds supplement their diet.

Southern muriquis consume food from 145 plant species. Their menu varies according to the season, linked to availability of their preferred food.

While the northern species practices geophagy, or “soil consumption”—they eat dirt—this behavior has not been documented in the southern species. 

Behavior and Lifestyle

Southern muriquis, like northern muriquis, are diurnal (active during daylight hours) and arboreal (spending most of their time in trees). Daily life for these monkeys consists of foraging, feeding, socializing, playing, and resting (about half their day is spent resting). Overnight, they sleep close together in the dense canopies of large trees.

Brachiation—swinging by their arms, hand over hand, from one tree limb to the next—is the main mode of travel for both species as they advance through the forest canopy. Southern muriquis typically move through the forest single-file while foraging, a strategy that reduces the risk of serious falls.

Muriquis are fast and agile. Both species are assisted by their long, prehensile tail. A bare patch of skin on the underside at the tip of the tail functions as a gripping pad, providing stability as the monkeys hang solely by their tail while feeding.

Unlike their sister species to the north, whose modus operandi of peace, love, and group hugs has earned the northern muriqui the nickname “hippie monkey,” southern muriquis are much less touchy-feely. And while civility reigns in the north, hostile encounters—even acts of violence against one another—are not uncommon in the south.

But southern muriquis may suffer from an unjustly besmirched reputation. Blame it on the males.

In the north, where the species feeds foremost on leaves, an abundance of leaves typically keeps members of a group together in a big, loving tangle while they eat. Aggressive behavior is rare. But in the south, where the species feeds foremost on fruits, fruit trees are widely scattered, necessitating that members forage farther from the main group. When too many females disperse, the males who remain behind have fewer mating opportunities. They become sexually frustrated—and aggressive.

In the course of a long-term study of southern muriquis, researchers documented a deadly attack on an older adult male by a group of younger adult males. An adult female and two unidentified individuals also took part. Scientific speculation suggests that an imbalance in the monkeys’ environment, related to food sources, led to the dispersal of female members; which, in turn, led to behavioral imbalances within the group; which led to tensions relating to mating competition; which, ultimately, triggered the vicious ambush. (This attack shares commonalities with attacks by chimpanzees on other chimpanzees, where a lone chimp is murdered by members of his group.)

Researchers hypothesize that imbalances of power, like those observed in southern muriquis, lead to intraspecific competition—and killing—not only with muriqui populations but also with other primates, including chimpanzees and humans.

Fun Facts

“Muriqui” is a native word of Brazil’s Tupi Indians; it means “largest monkey.”

The southern muriqui is known locally as mono carvoeiro, which means “charcoal monkey.”   ​

Muriquis’ alternative name of “woolly spider monkey” is misleading, assert some wildlife biologists. They believe that the name incorrectly implies that the monkeys are hybrids of woolly and spider monkeys—which they are not. Since 1995, the northern and southern muriqui has each been classified as a unique species.

Daily Life and Group Dynamics

Muriquis are social primates who live in family groups, or “troops.” Group size for southern muriquis ranges from 5 to 25 individuals (contrast to northern muriquis’ group size, which might include up to 80 individuals). Males are related to one another and remain with their natal (birth) group, while females, upon reaching adolescence, leave their natal group to join other troops. (More often with nonhuman primate species, males are the ones who depart their natal group.)

Southern muriquis’ expansive home range allows members plenty of room to forage, thereby minimizing territorial conflicts with outside troops. Should they find a fabulous fruit tree that another monkey has already claimed, however, they will chase the monkey away and claim the tree for themselves. If the succulent fruit has not yet ripened, southern muriquis patiently munch on the leaves—and wait.

While southern muriquis may not be big huggers, like those in the north, they are known to embrace one another on occasion.

Of the two species, southern muriquis are less inclined to descend to the ground. But as their treed habitat continues to disappear, as their sister species to the north has experienced, they may find themselves forced to do so for travel from one place to another.

Sympatric species include mountain lions, margays, and ocelots; these wild cats are also natural predators of southern muriquis, as are tayras (omnivorous weasels), who also share southern muriqui habitat. Peccaries (wild pig-like animals) live here, too.


Both southern and northern muriquis use a wide variety of vocalizations to communicate; many of these vocalizations are similar between the two species.

Neighs are contact calls, used to maintain group cohesion and to inform individuals about group movement. Southern muriquis are known to use neighs in the course of selecting sleeping sites. Barks indicate alarm. Shrill yips are given as an alert. Chuckles and warbles are often heard during embraces; the former is used to give reassurance, while the latter indicates excitement. Chirps convey a variety of meanings: at short distances, they can be used as “food calls” (think of ringing the dinner bell!); an individual who sounds a loud chirp is letting his group know that he has just discovered a great foraging area. Infants chirp (think of a human infant “cooing”) and keen (plaintively cry) when trying to get their mothers’ attention. Staccato (sharp, disjointed notes) chutter-whinnies are used during reunions. Twitters are sounded by females who are trying to attract a male to mating partner. “Kh-kh-kh” is a sound of contentment, heard by resting individuals. Screaming is heard from individuals who are lost, or from victims of an intraspecific attack.

While northern muriquis engage in what is known a “sequential exchange” (individuals take turns answering one another), this behavior has not been reported in southern muriquis.

Tactile communication is certainly a part of muriquis’ daily life. Embraces between individuals help to establish strong social bonds. Grooming instills strong bonds between a mother and her infant.

Pheromones leave important scent clues when it comes to mating.

Reproduction and Family

Muriquis are promiscuous, whether they are from the south or north. Both sexes enjoy multiple partners, making them polygynandrous.

Southern muriqui adult males are endowed with a large scrotum, and the females of the southern species have an elongated, cylindrical clitoris (researchers suspect that northern muriqui females are anatomically similar).

When she wishes to attract a male, a southern muriqui female urinates on her hands so that as she moves through the forest, she leaves a strong pheromonal scent trail for males to follow. Before taking a female up on her offer to copulate, a male may smell the female’s genitals or taste her genital secretions. The two may or may not copulate. Adult males have been observed consuming their excess ejaculate, perhaps for its high protein content, researchers speculate. (Researchers think that northern muriqui males may also engage in this curious behavior; they just have not been caught in the act.)

Southern muriqui females reach sexual maturity (capable of conceiving) at age 11; males reach sexual maturity (capable of siring offspring) much earlier, at age 5-1/2. The monkeys breed during Brazil’s wet season (October to March). After a gestation period of about 7 months, a single infant is born.

During their first year of life, young muriquis are almost completely dependent on their mothers. From 3 to 6 months old, the infant clings to his mother’s belly as she travels through the forest. At age 6 months, he begins riding on his mother’s back. Infants are considered weaned at 18 to 30 months. Young muriquis are considered to be independent at age 2, at which time they no longer get a free ride on their mothers’ backs.

Photo: Leonardo Desordi Lobo/ Creative Commons
​Ecological Role

Muriquis are important ecological ambassadors. They help to regenerate their forest environment by distributing seeds, via their feces, from the many fruits they eat.

Conservation Status and Threats

The southern muriqui, like the northern muriqui, is classified as Critically Endangered—only one step away from Extinction in the Wild—by the International Union for the Conservation of Nature (IUCN, 2019), appearing on the IUCN Red List of Threatened Species. Over the past 60 years (three generations), the overall population has declined 80 percent.

Habitat loss has taken a grim toll on the species. Tracts of forest have been razed for logging, coffee and timber plantations, illegal palm harvesting, agricultural use, cattle ranching, mining in buffer zones of protected areas, and human (urban) development.

Hunting is a parallel, and significant, threat to the species. The monkeys are killed both as a food source (“bush meat”) and for sport. Because of hunting, a dozen former populations of southern muriquis are victims of extirpation, or “local extinction.”

Today, only 1,100 to 1,200 individuals remain in the wild. They survive in 20 isolated areas in a mixture of private, municipal, state, and national protected areas. These individuals are in peril.

Conservation Efforts

The southern muriqui, like the northern muriqui, is listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.

Southern muriquis occur in several protected areas. In Rio de Janeiro, these areas include Reserva Ecologica de Guapiaçu (REGUA), host to the state’s largest population; extant populations are found in Itatiaia National Park, Serra dos Orgãos National Park, and Bocaina National Park. In São Paulo, protected areas include Parque Estadual Serra do Mar, Carlos Botelho State Park, and the State Forest Foundation of São Paulo. Muriqui Ecopark is a protected private reserve in São Paulo.

Just because some southern muriquis live in protected areas does not mean they are safe. Wildlife protection laws are not easy to enforce, and poachers who flout these laws are contributing to the species’ steady demise.

Furthermore, while those southern muriquis residing in Rio de Janeiro parks and reserves are afforded a modicum of protection from hunters (at least, in theory), they face a population decline because of fragmented habitat. As their habitat is increasingly lost, forest connections, or corridors, disappear. These corridors are relied upon by young females who leave their natal group to join a new group to reproduce.

To provide a backup for population extinctions in the wild, ensuring the fecundity of the species, conservationists call for improvements to captive breeding programs.

The National Action Plan Muriqui has authorized three captive breeding sites: Sorocaba Zoo (São Paulo), Passeio Publico Zoo, Curitiba (Paraná), and Rio de Janeiro Primate Centre. (Of the three, only Sorocaba Zoo has reported a measure of success. The zoo also receives wild-born muriqui infants each year, brought to the zoo by palm-harvesters and hunters who have killed the infants’ mothers.)

Overall, captive breeding programs have fallen short thus far. Low reproductive rates and infant deaths have hampered the mission.

Focusing on wild populations of southern muriquis, Associação Pró-Muriqui is a non-governmental organization (NGO) created in 2000 to ensure continued research activities within Carlos Botelho State Park, where field research began in 1986. In 2015, São Paulo launched the Pró-Primatas Comission, a permanent commission responsible for elaborating conservation policies for state-wide action on threatened primate species.

A glimmer of optimism exists thanks to the efforts of forest rangers working at Reserva Ecologica de Guapiaçu (REGUA). For the past decade, these REGUA rangers have successfully engaged with local communities through environmental education programs. As a result, hunting has markedly decreased in these areas.

“Keepers of the Wild” (a program of the World Land Trust) is committed to assisting REGUA in its mission. To learn how you can help, visit:


Written by Kathleen Downey, May 2021