Ateles hybridus

Geographic Distribution and Habitat

Brown spider monkeys (Ateles hybridus), also known as variegated spider monkeys, long-haired spider monkeys, and as Magdalena Marimonda by locals, are natives of South America, residing in the countries of Colombia and Venezuela.

In Colombia, these primates can be found along the western bank of the Magdalena River within the departments of Bolívar, Antioquia, and Caldas with an isolated population within the department of Santander. Most populations live within lowland forests below 3,281 feet (1,000 meters) above sea level, though some groups have been reported at altitudes as high as 5,840 feet (1,780 meters) above sea level. Additional populations live along the eastern bank of the Magdalena River within the departments of Magdalena and César (north of the southern slopes of the Sierra Nevada de Santa Marta Mountain Range). Others reside in the southwestern region of Guajira on the western and eastern slopes of the Serranía de Perijá Mountains (also known as Sierra de Perijá) toward the border with Venezuela; still, others make their home in central Río Magdalena valley extending to the departments of Boyacá and Cundinamarca.

Venezuela’s population of brown spider monkeys is geographically less contiguous than those living in neighboring Colombia. Populations here reside at elevations from 66 to 2,297 feet (20 to 700 meters). Within the state of Miranda (and possibly extending west into the state of Vargas), the monkeys are found in the north along the southeastern section of Cordillera de las Costa (Central Mountain Range). Either side of the Venezuelan Andean Cordillera (Venezuelan Andes), which forms the northernmost extension of the Andes Mountains Range, is home to brown spider monkeys. On the eastern side, these primates live within the piedmont (or foothills) of mesic forests (those occurring within moist areas of upland habitat) and within the lowland forests of San Camilo and Ticoporo, both areas highly threatened due to habitat destruction. On the western side, their distribution begins in the Andes piedmont, extends to the lowland region surrounding the southern area of Lake Maracaibo within the Río Catatumbo watershed in the department of Norte de Santander, and stretches to the Serranía de Perijá Mountains along the border with Colombia. An isolated population is found in northeastern Venezuela, residing within Parque National Guatopo, a national park and protected area.

Subtropical and tropical evergreen rainforests are the preferred habitat for the species, followed by riverine forests (where land and river intersect), marsh, and semi-deciduous forests.


Morphological and molecular analysis has proven the brown spider monkey to be a distinct species, dismantling the contention that it may have been a subspecies of white-bellied spider monkeys (Ateles belzebuth).

Not to be confused with the brown-headed spider monkey (Ateles fusciceps) of Colombia, Ecuador, and Panama, the brown spider monkey is one of seven species of spider monkeys.

Until recently, wildlife biologists had believed the species to be the “parent” to two subspecies: Ateles hybridus brunneus and Ateles h. hybridus. However, recent molecular studies prove otherwise. The brown spider monkey is a single taxon with no subspecies, or “children.”

Brown spider monkey range, IUCN 2023

Size, Weight, and Lifespan

These are big monkeys with robust frames. An adult male weighs between 17.4 to 22 pounds (7.9 to 10 kilograms). An adult female brown spider monkey weighs a bit less, between 16.5 to 19.8 pounds (7.5 to 9 kilograms). Head-to-body length for adult males is between 18.5 to 19.7 inches (47 to 50 centimeters); head-to-body length for adult females is slightly less, 17.7 to 18.9 inches (45 to 48 centimeters). Front legs are longer than hind legs. A slender, prehensile tail, longer than the body, adds another 30 to 33 inches (76 to 85 centimeters) to males and 29 to 30 inches (74 to 76 centimeters) to females.

Average lifespan for brown spider monkeys in their natural, wild habitat is about 22 years.


Spider monkeys take their name from their long, spindly, and hairy limbs that resemble the legs of a spider. Each of the seven species exhibits its own unique color pattern. As example, the discrete multicolored markings of the brown spider monkey give the species its alternate name of “variegated spider monkey.”

Varying shades of brown distinguish the pelage (fur coat) of this monkey. The fur on the back, outer side of limbs, and topside of the tail is a pale, sandy brown. Buff-colored fur on its abdomen and the inner side of its limbs gives the pelage a subtle contrast. Hands are hook-shaped with four elongated, curved fingers and a vestigial (almost absent) thumb that helps the monkeys grasp branches as they swing through the forest. The hairless inner tip of the tail, defined by ridged skin, assists in this acrobatic effort.

A crown of dark brown fur covers the head, allowing scalloped ears to peak out on either side. The forehead is distinguished by a buff-colored, triangular tuft of fur. Its expressive face is characterized by dark skin, a nondescript muzzle with wide nostrils that flare out, and narrow lips that are barely accented by sprouting hairs above and beneath. But the most arresting facial feature in certain individuals is eye color. Generally, these are brown-eyed beings; some brown-eyed spider monkeys, however, have pale blue eyes—a capricious or whimsical design by Mother Nature.


Fruits are awesome! That’s what brown spider monkeys would tell you if they could. More than 80 percent of their diet consists of fruits—making these primates a mainly frugivorous species. Ripe, fleshy fruits are preferred, plucked from the emergent trees in the upper parts of the rainforest canopy. In one study area in Las Quinchas, Colombia, the monkeys fed from 65 plant species, which included many berries, for a total fruit intake of 93.5 percent—top fruitiness even among wild brown spider monkeys! During the dry season, when fruits are not plentiful, these monkeys supplement their diet with young leaves, nuts, flowers, floral buds, seeds, decaying wood, and aerial roots. Termites and caterpillars are occasionally on their off-season menu, along with a sprinkling of spiders and bird eggs. For those brown spider monkeys trying to survive in fragmented habitats ravaged by anthropogenic (human-caused) activities, a larger quantity of young leaves is part of their year-round diet. Geophagia, the practice of eating soil, is thought to be practiced by the species as a means of absorbing nutrients and naturally balancing the pH levels (acid to alkaline) in the monkeys’ digestive system.

Behavior and Lifestyle

Brown spider monkeys are arboreal creatures, meaning they spend the bulk of their time in trees, hanging out in the upper forest canopy of the tallest and oldest trees. Visits to the forest floor are rare; when they do so, it’s either to drink water or eat soil. They are diurnal, meaning they are active during daylight hours. Come nightfall, they retire to their sleeping site within the forest canopy, strategically chosen near plentiful food sources and typically within the same tree each night.

With natural agility, brown spider monkeys appear to effortlessly move through their forest habitat via brachial locomotion, swinging by their arms from tree limb to tree limb aided by their mobile shoulder joints, covering distances as much as 30 feet (9 meters). They might also jump; their prehensile tail, a unique adaptation that functions as a fifth limb is capable of grabbing onto any substrate (surface); it helps to stabilize the monkeys as they advance through the forest canopy high above the forest floor. Their hook-like hands and flexible tails allow them to grasp and pluck fruits. On occasion, brown spider monkeys travel through the middle or lower strata but rarely visit the forest understory.

Some groups spend nearly their entire day foraging and feeding upon the succulent fruits these monkeys love so much, relying upon their senses of sight, smell, taste, and touch. The perfect piece of fruit might be enjoyed while hanging from a branch by their tails. Youngsters might engage in play sessions, hanging by their tails so that their hands are free to “wrestle” one another.

Natural wildlife predators to the species include pumas, jaguars, large snakes, and eagles. But by far the greatest predator threat to these primates are humans, who kill the monkeys for their flesh, known as bushmeat, and kidnap the babies (after killing the mothers) to supply the illegal pet trade.

It’s not surprising, then, that this species becomes agitated in the presence of humans, even when these humans are tourists with no nefarious intent. In an effort to scare away a would-be predator, human or otherwise, brown spider monkeys grab and violently shake nearby tree branches.

Fun Facts

The genus name Ateles means “imperfect,” a reference to the monkey’s vestigial thumb.

Spider monkeys are considered to be the third most intelligent nonhuman primate, behind orangutans and chimpanzees and ahead of gorillas and all other monkeys.

Daily Life and Group Dynamics

Brown spider monkeys are highly intelligent. Their mental capacity is thought to be an adaptation to their frugivorous (fruit-based) diets, which require that they identify and memorize many different fruits from a variety of fruit trees and the location of these trees.

They are charismatic, social animals who live in multimale/multifemale family groups (also known as “troops”) with up to 30 members. That’s a lot of individuals to successfully plan and get anything done. So before they head out for a day of foraging, members form much smaller subgroups consisting of several male and female individuals who travel, feed, and rest together. Adult males sometimes travel together in macho groups while females travel with their young. At the end of the day, subgroups rejoin one another as a larger group—a classic fission-fusion society.

Home range within heavily fragmented areas has been estimated between 74 to 297 acres (30 to 120 hectares). But this estimate is ten years old, and with the continued destruction of the species’ habitat, the actual home range size is likely much less in these areas. Brown spider monkeys who live in continuous, uninterrupted forestland are likely to have larger home ranges. Other spider monkey species who live in uninterrupted habitats can have home ranges as large as 988 acres (400 hectares).

The species displays no strong social hierarchy, though older individuals command more respect. Upon reaching puberty, females leave their birth group to seek a new troop to join where they might find a mating partner when they are ready to procreate.

In field studies, males were observed as being more aggressive to females than to males. Females were able to assuage this bad behavior and placate their testosterone-hyped male aggressors by grooming them. Aggression between females was reported as uncommon. These same field studies revealed occurrences of interspecies infanticide. Two subadult males attacked and killed an infant Colombian red howler (Alouatta seniculus) and an infant Humboldt’s white-fronted capuchin (Cebus albifrons).

Besides Colombian red howler and Humboldt’s white-fronted capuchin monkeys, other primate species who share habitat with brown spider monkeys include white-footed tamarins (Saguinus leucopus), cotton-top tamarins (Saguinus oedipus), gray-handed night monkeys (Aotus griseimembra), varied white-front capuchins (Cebus versicolor), Venezuelan brown capuchins (Cebus brunneus), Sierra de Perijá white-fronted capuchins (Cebus leucocephalus), weeper capuchins (Cebus olivaceus), and Santa Marta white-fronted capuchins (Cebus malitiousus). Of course, predators of the brown spider monkey live here, too: pumas, jaguars, large snakes, and eagles. The region is also home to red brocket deer (Mazama rufina), mountain tapir (Tapirus pinchaque), and spectacled bears (Tremarctos ornatus). The Andean condor (Vultur gryphus), Colombia’s national bird, and the Venezuelan troupial (Icterus icterus), Venezuela’s national bird, live here along with over 3,000 species of tropical birds, collective of Colombia and Venezuela.


Vocalizations attributed to brown spider monkeys include “whinnies,” loud calls used to transmit location while foraging and to identify group members; “ts chookis,” used to maintain contact with one another; whoops, moans, and cries of excitement, each used in various situations. As example, when subgroups come together as a larger group after a day of foraging, they enthusiastically greet one another with joyful calls. But they do more than just say, “Wonderful to see you again!” They hug one another. These are tactile, demonstrative, and affectionate primates. They further reconnect by sniffing one another’s sternal (chest) glands, breathing in the other’s pheromones to receive important olfactory information. Then they sit together, relaxing with their tails intertwined.

Reproduction and Family

Like other primate species of the genus Ateles, brown spider monkeys are believed to be polygynandrous (promiscuous); that is, both males and females take numerous mating partners. But in this matriarchal society, females decide upon the males with whom they wish to procreate. Though she attains sexual maturity at about 4 or 5 years old, a female is typically between 7 and 8 years of age when she first gives birth. After a gestation period of 7.5 months, a single infant is born. The birth interval for the species is between 3 and 4 years, at which time a female again reproduces. Births occur year-round, peaking during the early rainy season between May and July.

Initially, newborns cling to mom’s tummy, but soon afterward they transfer to her back. They make use of their versatile prehensile tail, wrapping it around mom’s tail for added security, like a seatbelt, as they ride atop her while she swings through the forest. Moms nurse their infants for 12 to 20 months, at which time infants are considered weaned. Mothers teach their young important social and survival skills, including how to forage. At about 20 months of age, young brown spider monkeys are independent, able to navigate their environment, and take their place within the family group.

Ecological Role

What would their rainforest forest ecosystem be without them? Brown spider monkeys are an integral part, and vital citizens, of their tropical rainforest home. Seeds of the many fruits they eat pass through their digestive tract are excreted through their feces and scattered throughout their habitat to nourish the ecosystem, encouraging new tree growth so the trees, in turn, provide the monkeys with food and shelter. It is a reciprocal, symbiotic relationship.

Interestingly, wildlife biologists have discovered that the monkeys don’t necessarily have to travel to disperse seeds. When large troops of brown spider monkeys gather in trees overnight to sleep, they do what you’d expect them to do when Nature calls (and they are in nature, after all): they poop. That’s a lot of poop dropped to the forest floor below, enriching the earth with nutrients to help grow more trees and bettering the rainforest ecosystem for all the animals who live here.

Conservation Status and Threats

Brown spider monkeys are classified as Critically Endangered by the International Union for Conservation of Nature (IUCN, March 2020), appearing on the IUCN Red List of Threatened Species. They also have the ignoble distinction of appearing six times on The World’s 25 Most Endangered Primates. While a total population count is not provided, the IUCN predicts a population reduction of greater than 80 percent over the next 45 years (three generations of the species). Global Forest Watch attributes this dire prediction to the impending loss of suitable habitat, at least 30 percent within this timeframe.

Continuing loss of suitable habitat through fragmentation and degradation is a grave threat to the species’ survival. Brown spider monkeys are on the brink of extinction. As pristine forest is razed through slash-and-burn agricultural practices and converted to tracts of land for cattle, roadways, and human settlements, or felled by the logging industry, brown spider monkeys are being evicted from their homes in nature at an alarming rate and forced into isolated patches of habitat. Few larger healthy populations remain. Without large areas of forest, there simply aren’t enough trees to provide the fruits that fulfill the monkeys’ nutritional requirements. The species’ long interbirth intervals also conspire against the brown spider monkeys’ ability to recover from anthropogenic threats.

In addition to being heavily hunted and killed for their flesh (whether for sustenance or for local bushmeat markets) and to furnish the illegal pet trade, brown spider monkeys are killed and dismembered so their body parts can be used in traditional medicines.

Of course, the Earth’s climate crisis looms over these spider monkeys as it looms over all our planet’s inhabitants.

Conservation Efforts

Brown spider monkeys are listed in Appendix II 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.

Although subpopulations of brown spider monkeys are reportedly found in several protected areas within Colombia and Venezuela, no information is available about the species’ status—including whether these monkeys are actually protected. As example, within the region of San Lucas National Park in Colombia, the presence of political insurgents, the military, and minefields makes the area perilous to conservationists who would conduct population surveys. And in Venezuela, laws against hunting and logging within designated protected areas are routinely flouted, leaving the monkeys unprotected.

Conservationists call upon government agencies to drastically improve and enforce protections, in part by increasing the number of park rangers, and to implement more local community education programs to raise awareness about the species. They also call for more field studies and population surveys.

Primates Project Foundation (Fundacion Proyecto Primates), based in northeastern Colombia and led by primatologist-conservationist Andrés Link, is a conservation organization dedicated to saving brown spider monkeys from extinction. Between July 2018 and June 2019, the organization implemented a project to reconnect main forest fragments in Cimitarra within the department of Santander with a goal of increasing the long-term resilience of wild populations here. Fifteen forest fragments were sampled and the monkeys studied.

Highlights of the project include the creation of three forest nurseries that produced 12,000 plants, allowing for the establishment of six forest corridors; the renewal of two voluntary conservation agreements with local landowners; community education and species awareness /biodiversity workshops geared to both adults and children; training of new wildlife biologists and environmental engineers. A brown spider monkey festival was also held, with 500 people attending!

One unexpected, and notable, discovery during the monkey study aspect of the project was the presence of two individuals, brothers, who were completely white. Link referred to the two albinos as “ghost monkeys.” He described the primates as very beautiful but added that their albinism, likely a consequence of inbreeding and loss of genetic variability, had almost certainly destined them to extinction and it tells a sad story about the species. Ghost monkeys, Link warns, face additional struggles surviving in their environment because their mutation has rendered them unable to cope with a changing landscape. Thus, the ongoing initiative to reconnect isolated populations with one another, and strengthen the species’ gene pool, must be regarded as an urgent undertaking.

  • Variegated or Brown Spider Monkey Ateles hybridus Geoffroy, 1829 Colombia, Venezuela (2004, 2006, 2008) Erwin Palacios, Alba Lucia Morales-Jiménez & Bernardo Urbani:
  • Primates Projects Foundation:


Written by Kathleen Downey, March 2024