Brachyteles arachnoidesmuriqui(Also: woolly spider monkey)

Geographic Range

Woolly spider monkeys, or muriquis, are found scattered throughout the southeast of Brazil, ranging from Bahia in the north to Sao Palo in the south. They make their home in the lonely remnants of their coastal Atlantic forest habitat. (Massicot, 2001; Strier, 1992; Moynihan, 1976)


The preferred habitat of Brachyteles arachnoides is the mature evergreen and deciduous lowlands of the costal Atlantic forests in Brazil. B. arachnoides is arboreal and spends most of its time in the canopy. However, muriquis are quite resilient despite their endangered status. Troops will utilized both primary and secondary growth in pristine as well as disturbed areas. Although they are highly arboreal, they will cross open ground when there are gaps within the canopy. (Strier, 1992; Massicot, 2001)

Physical Description

The muriqui is the largest South American primate, with males weighing about 15 kg, and females about 12 kg. The head and body length has been reported as 780 mm, and the tail is about the same length. When they are seen hanging by their arms, they measure about 1.5 meters tall.

Muriquis have very long prehensile tails, which aid them in their arboreal existence. Because of the swinging nature of their movements, their thumbs have become reduced in size and are considered vestigial. Both sexes have prominent pot bellies. The coat is grayish-golden except for the face, which looks as if its been covered with soot, and the area surrounding the genitals, which tends to be much redder in color than the rest of the body. The genitals in this species are fairly conspicuous. The male has a large os penis, and the female clitoris is very long and tipped with reddish hair.

(Napier and Napier, 1985; Strier, 1992; Massicot, 2001; Monihan, 1976)

  • Sexual Dimorphism
  • male larger
  • Average mass
    12-15 kg
  • Average mass
    11170 g
    393.66 oz
  • Average length
    780 mm
    30.71 in


There does not appear to be much competition between males for mating oportunities. Often, males will wait in line for their chance to mate with a receptive female. Both males and females have multiple mating partners. Females are able to exert more choice in mates than in many primate species, because of the minimal sexual dimorphism in this species. Females also exert some mate choice when they decide what group of males to join when they disperse from their natal group at adolescence.

(Strier, 1992; Massicot, 2001)

The age of sexual maturity has been recorded as approximately 11 years for a female and 5.5 years for a male. Their courtship is extremely passive. There is very little agression between males, and they seem extremely tolerant of each other. The males sometimes wait in line for their opportunity to mate with a receptive female.

When it comes to choosing a mate, females are very much in charge, which is unusual for primates. Since both sexes are approximately the same size, the males cannot bully the females into giving in. After mating, gestation lasts 7-8.5 months, when the female gives birth to a single young in the dry season (May though September). A baby muriqui is born 7-8 ½ months after it is conceived.

(Strier, 1992; Massicot, 2001)

  • Breeding season
    Most births occur during the dry season, from May to September.
  • Average number of offspring
  • Average number of offspring
  • Range gestation period
    7 to 8.5 months
  • Range weaning age
    18 to 30 months
  • Range age at sexual or reproductive maturity (female)
    6 to 11 years
  • Range age at sexual or reproductive maturity (male)
    6 to 11 years

Parental care is prinicpally the business of females. Young are quite helpless when born, although able to cling to their mother's fur. For the first few weeks of life, the infant clings to its mother's side, under her arm and near the nipple. By 6 months of age, the baby rides "jockey style" on its mother's back as she goes off to forage. After 6 months, an infant muriqui will begin to assert some independence, exploring the surrounding world but never leaving its Mom’s side by more than a few feet.

After the toddler has reached a year, it will wander off for longer periods and interact with other toddlers. At times its mother will leave it while she goes to forage. The mother will call her baby back when she is done. By this time the toddler is starting to eat some on its own. This idyllic existence between mother and baby ends abruptly when weaning occurs and the mother chases off her child. Weaning time varies, from 18 to 30 months of age, averaging 24 months. Often weaning involves pecking and nipping by the mother, with loud cries from the confused baby, who may go on screaming for 15 minutes or more. The baby will often find comfort with other confused weanlings who are going through a similar experience.

In adolescence (4-6 years) the youngsters will start to move their own separate ways. The young males will attempt to make stronger bonds with the other males in the group and the young females will begin to distance themselves as they prepare to leave and join another troop.

The male role in parental care in this species has not been reported.

(Strier, 1992; Massicot, 2001)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female
  • post-independence association with parents
  • extended period of juvenile learning


The average life expectancy of this species is unknown.

(Strier, 1992; Moynihan,1976)


Muriquis are nearly completely arboreal. They are active during the day.

Muriquis are well adapted to life in trees. Their long arms and vestigial thumbs make it easy for them to hurl themselves from one branch to the next. When moving from one foraging area to another, a troop will often travel in line, with one monkey following another through the forest. This allows them to avoid serious falls because all except the first muriqui in line is utilizing well used and tested branches.

Unlike many other primate species, muriqui females exert a great deal of control in social interactions. In this species, the males and the females are very nearly the same size. Because of this, the males cannot bully the females into submission.

This is one of a few groups of primates where the males stay with their natal group and the females are the ones to leave to join other troops. Troops maintain a home range in which they forage, and are nomadic within that home range, going from one food source to another.

Members of a troop are not very aggressive towards each other, which is said to be unusual for primates. This behavior probably derived from the fact that they are so arboreal. If they do fight, there is a great risk of falling out of the tree.

(Strier, 1992; Massicot, 2001)

Communication and Perception

Food Habits

Muriquis eat mostly fruit, leaves, flowers, and a few species of seeds. Fruit seems to be the choicest item in their diet. Due to their large size and the large number of individuals in their social groups, they can easily locate a fruit source and chase off other monkeys that are already exploiting it. Once they find a good foraging area, muriquis will often camp out, waiting for days eating leaves until the fruit is ripened.

Foods eaten include: ripened fruit, leaves, flowers, seeds of Sapucainha, seeds of Amexia-bicha, seeds of Inga, seeds of Bicuiba and seeds of Jatoba.

(Strier, 1992)

  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit
  • flowers


The major predation threat to muriquis is from indigenous humans. These monkeys have been hunted for food because their meat is considered a delicacy in the areas where they are found. Although some troops of muriqui may be an important food source for large predators such as jaguars, ocelots, and harpy eagles, there are not many confirmed cases of this type of predation. One troop that was observed for a decade lost only five members in that time, and only two of those five disappeared mysteriously.

(Strier, 1992)

Ecosystem Roles

Muriquis serve an important ecosystem role in dispersing seeds throughout the forest. One study showed that seeds collected from muriqui feces and then planted almost always germinated. In some cases, the seeds germinated faster than those that never passed through a muriqui digestive system.

B. arachnoides may also have some impact on predator populations, but because of its own low population size, it is unlikely that any predators rely very heavily on this species as a food source.

(Strier, 1992)

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Since the early 1990’s, muriquis have been targeted by eco-tourists. The popularity of South America's largest primate, particularly on the Fazenda Montes Claros Plantation, has been increasing throughout the years. Tourists bring in dollars for both the local people and the government.

This species has also been hunted by indigenous people. Its meat is considered a delicacy.

(Strier, 1992)

Economic Importance for Humans: Negative

Muriquis are not abundant enough to have negative economic impacts, though they are primates and are succeptable to many of the same diseases humans are. Being an endangered species in a degraded situation, disease is more likely to spread.

(Strier, 1992)

Conservation Status

Muriqui populations are estimated to have been in the hundreds of thousands prior to the European colonization of South America. Populations of these primates are thought to have been spread throughout the continent. Today, there are fewer than 500 individuals known to persist in the scattered fragmented forests of coastal Brazil. The species is listed on the IUCN Red List of threatened species and has been considered critically endangered since the year 2000. CITES lists these animals as Appendix I, the most endangered status they have. Muriquis are also listed as endanged by the United States Fish and Wildlife Service. Efforts are being made to study this species in the attempt to develop a management plan. Without a management plan, extinction is imminent.

(Strier, 1992; Massicot, 2001)


Anni Bladh (author), Humboldt State University, Brian Arbogast (editor), Humboldt State University.



living in the southern part of the New World. In other words, Central and South America.

World Map


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates


humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


an animal that mainly eats leaves.


A substance that provides both nutrients and energy to a living thing.


an animal that mainly eats fruit


An animal that eats mainly plants or parts of plants.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


generally wanders from place to place, usually within a well-defined range.


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


Massicot, P. August, 19, 2001. "Animal Info - Muriqui" (On-line). Accessed October 25, 2001 at

Moynihan, M. 1976. The New World Primates. Princeton, New Jersey: Princeton University Press.

Napier, J., P. Napier. 1985. The natural history of the primates. Cambridge, Massachusetts: The MIT Press.

Strier, K. 1992. Faces in the Forest. New York, New York: Oxford University Press.