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Conservation status:
Critically endangered (B. hypoxanthus), Endangered (B. arachnoides)

Life span: Unknown
Total population: 700 (wild)
Regions: Brazil
Gestation: 7.2 months (216 days)
Height: 490 mm (M), 486 mm (F)
Weight: 9.6 kg (M), 8.4 kg (F)

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Suborder: Haplorrhini
Infraorder: Simiiformes
Family: Atelidae
Subfamily: Atelinae
Genus: Brachyteles
Species: B. arachnoides, B. hypoxanthus

Other names: woolly spider monkey; ulden edderkoppeabe (Danish); spinaap (Dutch); muriki (Finnish); atèle arachnoïde, eroïde, or singe-araignée laineux (French); spinnenaffe (German); murichi (Italian); mono arena, mono carvoeiro, mono grande, muriki (Spanish); kortullig spindelapamirikinordlig ullspindelapa; mirikinordlig ullspindelapa, ullhårig spindelapa, ullig spindelapa, or ullspindelapa (Swedish); B. arachnoides: muriqui, woolly spider monkey, southern muriqui, or southern wooly spider monkey; B. hypoxanthus: muriqui, northern muriqui, or northern woolly spider monkey

The name muriqui comes from the Tupi Indians of Brazil, but they have also previously been called woolly spider monkeys. The use of the name woolly spider monkey has fallen out of favor, as the term is misleading, implying that the animal is a hybrid of woolly monkeys (Genus Lagothrix) and spider monkeys (Genus Ateles), when in fact muriquis are unique (da Fonseca 1985a; Strier 1992a). Once considered to be two subspecies, B. a. arachnoides and B. a. hypoxanthus were elevated to species level in 1995 based on geographic distribution as well as morphological differences. The two species are completely geographically isolated from each other and interbreeding is not possible in the wild (Strier 1986; Rylands et al. 1995; Groves 2001).


The common name for members of the genus Brachyteles, woolly spider monkey, comes from the thick, fleecy appearance of their fur. They range in color from gray to yellow-brown and fur covers their bodies except for their faces, which are bare. The two species are distinguished from each other as the northern species, B. hypoxanthus, has a black face while the southern species, B. arachnoides, has a black face mottled with pink. Northern muriqui infants are born with black faces which become mottled as they age (Lemos de Sá et al. 1993; Strier & da Fonseca 1996/1997; Groves 2001). In addition to the difference in facial skin pigmentation, northern and southern muriquis vary in dental morphology. The canine teeth of male southern muriquis are much longer than females of the same species and longer than those of northern males. There is no sexual dimorphism seen in the canine teeth of northern males and females (Lemos de Sá et al. 1993; but see Leigh & Jungers 1994).

Another difference between the two species is the presence of an opposable thumb. Among southern muriquis, the external thumb is entirely missing while in northern muriquis, there is a vestigial thumb; it is rudimentary and abbreviated compared to other species of primates (Rosenberger & Strier 1989; Lemos de Sá & Glander 1993; Groves 2001). Even though they do not have a true thumb, this does not mean that muriquis are less evolved than other primates. In fact, the muriqui's ancestor had a thumb, but over time the hand became more specialized and the thumb shrunk. One hypothesis is that the thumb was no longer an essential part of locomotion as the prehensile tail evolved (Hartwig 2005). All muriquis have a prehensile tail, a specialized tail used in suspensory locomotion that is seen only in a few species of New World monkeys. Both the small or absent thumb and the prehensile tail seen in muriquis are related to the patterns of movement that characterize the genus: suspensory climbing and rapid brachiation (Rosenberger & Strier 1989). On the underside of the tip of the tail is a patch of bare skin or friction pad, which aids in grip. Having a 'third hand' allows muriquis to grasp branches for stability during travel or while feeding, to increase fluidity of motion during travel, and to hang solely by their tails to reach foods with both free hands (Rosenberger & Strier 1989). Muriquis are the largest of the New World monkeys, appearing almost five feet tall when hanging by their long arms from tree branches. In both species, males and females are about the same size, with adult males weighing 9.6 kg (21.2 lb) and adult females weighing 8.4 kg (18.5 lb) on average. Height from the head to the base of the tail is 486 mm (1.59 ft) in females and 490 mm (1.61 ft) in males (Lemos de Sá & Glander 1993). These are currently the best estimates for weight and body size available for both species, but they are based on a small sample size (five males and seven females, various ages). As more animals are captured and measured, the average heights and weights may change and reveal differences in size between the sexes (Lemos de Sá & Glander 1993; Peres 1994).


Brachyteles arachnoides | Brachyteles hypoxanthus

In the wild, muriquis are restricted to small, isolated patches of Atlantic coastal forest in Brazil (Lemos de Sá et al. 1993; Strier 1992a). They are distinctly separated into northern and southern regions with the northern region including populations in the states of Minas Gerais, Espírito Santo, and Bahia and the southern population existing in the states of southern Minas Gerais, southern Rio de Janeiro, and São Paulo (Strier 1992a; Pope 1998). The populations are separated not only by human development and lack of contiguous forest but also by riverine barriers such as the Rio Grande, the Rio Paraiba do Sul, or the Serra da Mantiqueira (Lemos de Sá et al. 1993).

Long-term research on northern muriquis has been the work of Karen Strier and her Brazilian colleagues since 1982 at the RPPN Feliciano Miguel Abdala (previously known as the Estação Biológica de Caratinga) on Fazenda Montes Claros, a privately owned ranch (Strier 1986; Strier & Boubli 2006). This privately owned property has been protected by the landowner and has been the source of many major discoveries about muriqui behavior and biology. Northern muriquis have also been studied at Fazenda Esmeralda in Minas Gerais, Reserva Biologica Augusto Ruschi in Espírito Santo, and additional field studies are underway at other sites in these states (Dias et al. 2005; Mendes et al. 2005). Important study sites of southern muriquis include Fazenda Barreira Rico and Parque Estadual de Carlos Botelho in São Paulo State (Milton 1984; Talebi et al. 2005). The muriqui population at Carlos Botelho lives in one of the largest undisturbed tracts of Atlantic coastal rainforest where muriquis can be found (de Moraes et al. 1998; Talebi et al. 2005).

There are fewer than 2000 muriquis remaining in the wild (Strier 2000; Mittermeier et al. 2005). The captive population of muriquis is tiny and according to the International Species Information System, a database for animals kept in captivity around the world; there are only two captive populations and they are found in Brazil ( Captive breeding efforts have been met with limited success because muriquis have not been removed from the wild to start a captive population. The captive stock in breeding facilities such as the Centro de Primatologica do Rio de Janeiro is entirely composed of sick or orphaned animals brought to them which must be nursed back to health. Because they do not draw from wild populations, they cannot choose which species or sex to bring into captivity and must rely on fate to develop a breeding population (Strier & da Fonseca 1996/1997). A captive population of southern muriquis is also housed at the zoo in Curitiba, Brazil (Strier pers. comm.).


All wild muriquis are found in highly fragmented patches of Atlantic coastal forest, a once widespread ecosystem spanning several states on the southeastern coast of Brazil which has been reduced in size to less than 5% of its original area (Strier & da Fonseca 1996/1997). Originally, the Brazilian Atlantic coastal forest was an area of exceptional species diversity and high levels of endemism but over time, as forest has been cleared for crops, pastures, timber, and human settlement, the forests have been severely altered (da Fonseca 1985b). Despite this rampant habitat destruction, muriquis survive in several isolated patches of both primary and secondary forests between 600 and 1800 m (1969 and 5906 ft) above sea level and exhibit flexibility in their habitat requirements (da Fonseca 1985a; Strier 1987a; Lemos de Sá & Strier 1992).

Southern muriquis studied at Fazenda Barreiro Rico in São Paulo State live in tall, primary semideciduous forest with some patches of secondary growth. While they prefer the older, taller areas of forest, they are capable of using disturbed patches and find vines to feed on in these lower areas (Milton 1984). The average annual rainfall at Barreiro Rico is 1263 mm (4.14 ft), with the heaviest rainfall concentrated in a six-month period from October to March. Less rain falls from April to September. The wettest months of the year are December and January while the driest months of the year are July and August. The annual temperature ranges between 8° and 35° C ( 46.4° and 95° F), and can get as cold as 0° C ( 32° F) (Milton 1984). In the large area of undisturbed Atlantic coastal forest at Parque Estadual de Carlos Botelho, primary, late successional forest can be found and annual rainfall averages 1685 mm (5.53 ft) (de Moraes et al. 1998).

In the north, muriquis live in variable conditions and exploit both primary forest, where available, as well as highly disturbed areas of secondary vegetation (Lemos de Sá & Strier 1992). At Fazenda Montes Claros in Minas Gerais, average annual rainfall is between 1000 and 1200 mm, with the rainy season lasting from November through April and the dry season extending from May through September (Strier et al. 2001). Temperatures vary from 12° to 29° C (53.6° to 84.2° F) throughout the year (Strier 1986). The forest composition at this study site has been dictated by human use patterns and ranges from undisturbed primary forest to regenerating secondary forest and scrub forest (da Fonseca 1985a). The dominant tree species are not the same as those found in São Paulo, and forest composition differs greatly between the two sites, further amplifying the ability of muriquis to cope with a diversity of habitat availability (Strier 1986).


Muriquis have physical adaptations allowing them to exploit both large quantities of leaves as well as move efficiently between fruit trees that are dispersed over large areas. Folivorous primates are generally large-bodied, have specialized digestive tracts to maximize nutritional gains from a comparatively poor food resource- leaves- and have dental adaptations for chewing and breaking down huge amounts of fibrous leaves (Zingeser 1973). Frugivores, which consume a high-quality, nutrient rich resource have adaptations most effectively forage for these resources which are less abundant and more widely dispersed than leaves (Gaulin 1979). Muriquis exhibit dental and gastric adaptations for consuming leaves as well as a prehensile tail and hook-like hands for traveling quickly and efficiently between fruit trees and indeed their diet reflects this folivorous-frugivorous diet combination (Strier 1987a).

The majority of their diet is composed of leaves and fruit, but they also eat flowers, bark, and buds (Strier 1991a). There are differences in the amount of leaves and fruits consumed when comparing northern and southern muriquis as well as between study sites. At Fazenda Montes Claros, diet varies according to resource availability throughout the year, but annually they spend 51% of their time feeding on leaves, 32% to fruits, 11% to flowers, and 6% to other foods such as bark, bamboo, buds, and ferns (Strier 1991a). They spend a higher percentage of their time feeding on fruit when it is available and more time feeding on flowers when they are abundant. Leaves are an important source of energy throughout the year, and they eat leaves consistently throughout the year to add bulk to their diet (Strier 1991a). At Fazenda Barreiro Rico, muriquis are more folivorous compared to Montes Claros, spending 67% of their time feeding on leaves and only 21% on fruits and 12% on flowers (Milton 1984). One possible reason the diets of the two species are divergent is because of the difference in forest structure at the study sites. Montes Claros has larger trees more likely to supply fruit whereas the forest at Barreiro Rico is mostly regenerating and has far fewer large, fruiting trees and more vines (Strier 1986). In pristine forests within their range, southern muriquis exhibit higher levels of frugivory than northern muriquis, indicating the reliance on leaves in other areas is directly related to lower levels of fruit availability due to habitat degradation and fragmentation (de Carvalho et al. 2004; Talebi et al. 2005). At Parque Estadual Carlos Botelho in southern São Paulo state, muriquis spend 71% of their time feeding on fruit compared to 24% on leaves. The remaining feeding time is spent on other food items. When ripe fruits are scarce, southern muriquis at Carlos Botelho consume unripe fruits in small amounts and supplement their diet to a greater degree with leaves, compared to other times of the year (Talebi et al. 2005).

The daily activity patterns of muriquis includes resting, feeding, traveling, and socializing. They have been described as inactive compared to other species of primates, and spend an average of 49% of their day resting compared to 29% traveling, 19% feeding, and 2% socializing and engaging in other activities (Milton 1984; Strier 1987b). The muriquis of Barreiro Rico are late risers, getting up between 8:00 and 10:00 a.m. and feed while traveling until the afternoon, when they have a period of rest lasting between two and three hours. They feed heavily in the late afternoon hours before retiring to their sleeping site for the evening around dusk (Milton 1984). At Montes Claros, travel patterns vary by season. In the summer, muriquis wake up and begin to travel as the sun rises, spending the mornings traveling and feeding and taking an afternoon rest beginning at midday, when temperatures are at their peak. On cold winter mornings, they do not begin to stir until mid-morning and are more leisurely in their pace, spending time to warm themselves in the sun and retiring earlier than in the summer months (Strier 1987b; 1992a).

At Montes Claros, the study group of northern muriquis lives in a home range of 1.68 km² (.649 mi²) which overlaps with another group in this protected forest. Day range length estimates range between 141 and 3403 m (.088 and 2.11 mi) but average 1283 m (.797 mi) traveled each day (Strier 1987a). During the wet season, from November to April, muriquis travel substantially longer distances compared to the dry months, which are between May and October (Strier 1986). Compared to southern muriquis at Fazenda Barreiro Rico, whose home range of .70 km² (.27 mi²) and average daily path length 630 m (.391 mi), northern muriquis at Montes Claros travel farther over larger home ranges (Milton 1984). This may be in response to the difference in quality of the habitat at the two sites. At Montes Claros, large food patches are common and the muriquis travel further to accommodate the larger group size in order to decrease feeding competition between group members. At Barreiro Rico, where there are fewer muriquis living in smaller groups and highly dispersed patches of quality food resources, the monkeys travel less distance. The feeding competition is not as high among the southern muriquis, and the added energy of traveling great distances between trees is not worth the return (Strier 1986; 1987a; Lemos de Sá & Strier 1992). At Carlos Botelho, the home range size of a group of muriquis is much larger than at Montes Claros and Barreiro Rico, averaging eight square kilometers (3.09 mi²) and owing to the larger tracts of forest found in the park than anywhere else that muriquis are studied (de Moraes et al. 1998). Despite having more and larger food patches, muriquis at Carlos Botelho live in smaller groups than at Montes Claros. One reason for this grouping pattern may be that in order to have the most frugivorous diet possible, smaller parties are necessary to exploit the resources efficiently. The other consideration is that muriquis at Montes Claros live under unnaturally strained conditions in terms of space available and population density but have adapted to maximize their diet (de Moraes et al. 1998).

Natural predators of muriquis include felids, such as jaguars, as well as raptors, but because top predators require large home ranges, the isolated patches of forest in which muriquis live do not support these animals in high enough numbers to create a critical threat for muriquis at Barreiro Rico and Montes Claros. Furthermore, where there are few natural areas to hunt surrounded by areas of human agriculture, predators sometimes survive on livestock, lowering the human tolerance for these animals and increasing persecution and decreasing overall predator populations (Lemos de Sá & Strier 1992; González-Solís et al. 2001; Chiarello 2003). Other smaller potential predators include mustelids, which have been circumstantially linked to the disappearance of infant muriquis at Montes Claros (Printes et al. 1996). The predator population at Carlos Botelho is more intact than at the other study sites and can support large animals such as jaguars, which could contribute to muriqui mortality at this site (de Moraes et al. 1998).

Content last modified: August 30, 2006

Written by Kristina Cawthon Lang. Reviewed by Karen Strier.

Cite this page as:
Cawthon Lang KA. 2006 August 30. Primate Factsheets: Muriqui (Brachyteles) Taxonomy, Morphology, & Ecology . <>. Accessed 2020 August 11.