GEOFFROY'S SPIDER MONKEY
Geographic Distribution and Habitat
Geoffroy’s spider monkeys, also called black-handed spider monkeys, are native to Central America. Their range includes Mexico, Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama. An arboreal (tree-dwelling) species, this New World monkey hangs out in the upper levels of the forest canopy in a variety of forestland, including rainforests, evergreen, mangrove swamp, semi-deciduous, cloud forests, and montane (upland slope) forests.
Size, Weight, and Lifespan
The Geoffroy’s spider monkey is one of the largest of the New World monkeys, with the male of the species being slightly larger than his female counterpart. The tails of both males and females are longer than their respective bodies, and their arms are longer than their legs.
Head-to-body length in male Geoffroy’s spider monkeys ranges from 1.3 to 2 ft (39 to 63 cm), with a weight between 16 and 20 lbs (7.4 to 9 kg). The length of the male’s tail ranges from 2.3 to 2.8 ft (70 to 86 cm).
Head-to-body length in female Geoffroy’s spider monkeys ranges from 1 to 1.5 ft (31 to 45 cm), with a weight between 13 and 18 lbs (6 to 8 kg). The length of the female’s tail ranges from 2.1 to 2.5 ft (64 to 75 cm).
Maximum life span in the wild is unknown. In captivity, the Geoffroy’s spider monkey can live from 33 to 47 years.
Spider monkeys are named for their extremely long, slender, “spidery” limbs. Their prehensile tail functions as a fifth limb, having adapted over the years to allow for grasping and manipulating objects. The versatility and strength of this tail is most evident during suspensory feeding, when the monkeys hang, suspended from a tree branch around which they have wrapped their tail, while foraging for food. Long, hook-like fingers allow the monkeys to swing from tree to tree beneath the forest canopy with ease, with no help necessary from a vestigial thumb that evolution has rendered a functionless stub. Like other monkeys and apes, Geoffroy’s spider monkeys have opposable big toes on their feet that can grab onto branches easily.
As their name implies, the hands and feet of the Geoffroy’s spider monkeys are black. Their fur coats vary in color from light buff to reddish-brown or black. Infants are born black, but their fur lightens in color during their first five months of life.
A smallish head sits atop a lithe body. Their expressive faces are hairless, with unpigmented skin framing the eyes and muzzle in a pale facial mask.
In what might be a case of primate penis envy, the female Geoffroy’s spider monkey is endowed with a protruding, oversized dangling clitoris (known as a “pendulous clitoris”) that resembles the flaccid penis of the male Geoffroy’s spider monkey—except the female’s organ is larger.
Primatologists believe that the enlarged clitoris of female Geoffroy’s spider monkeys helps the males decide which female to approach for mating. It allows the males to gauge a female’s sexual receptiveness. By touching the females’ clitorises, then smelling their own fingers to detect olfactory cues, males are able to determine a female’s reproductive status.
Geoffroy’s spider monkeys have a penchant for ripe and fleshy fruits; in fact, 80 percent of their diet is comprised of various fruits. Their color-vision eyesight allows them to easily select their favorites. They supplement their diet with leaves, flowers, buds, and occasionally bark, nuts, seeds, insects, spiders, and eggs. Young leaves provide the protein that can be lacking in fruit. Besides providing much of the monkey’s nutritional needs, fruits and leaves provide much of their water requirements. Like other spider monkeys, Geoffroy’s spider monkeys will drink water from tree holes and from water gathered on leaves; unlike other spider monkeys, however, they will also drink water from terrestrial (land) sources.
Behavior and Lifestyle
The Geoffroy’s spider monkey’s means of locomotion includes climbing, walking or running on four limbs along delicate branches, swinging from tree limb to tree limb using their arms in a feat of arboreal locomotion known as “brachiation,” and swinging by their tail in suspensory locomotion. But the most common method that these forest acrobats employ to move from tree to tree is called “bridging.” In this feat, the monkeys grasp a branch from a facing tree and pull themselves toward the tree until they are able to climb onto it. Acrobatic airborne leaps are not uncommon.
The genus name Ateles means “imperfect,” a reference to the monkey’s vestigial thumb.
The species name geoffroyi is in honor of French naturalist Étienne Geoffroy Saint-Hilaire.
Geoffroy’s spider monkeys sometimes rub a mixture of saliva and grounded lime tree leaves on their fur as a natural insect repellent.
Although they do not use tools, spider monkeys, including the Geoffroy’s spider monkey, are considered to be the third most intelligent nonhuman primate, behind only orangutans and chimpanzees and ahead of gorillas and all other monkeys. 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.
Highly social animals, Geoffroy’s spider monkeys live in multi-male, multi-female groups averaging 30 individuals, although groups of up to 100 have been reported. Group size varies with habitat type and depends largely on the available food sources in an area. Geoffroy’s spider monkeys are diurnal, which simply put means that they are most active during the daylight hours. They spend this time in the forest canopy foraging for food. Mornings are spent gorging themselves, while afternoons are reserved for rest.
For the purposes of foraging, particularly when food is difficult to find, larger groups will split into smaller subgroups—culinary search committees—and usually regroup in the evening. However, for groups as large as 100, the entire group might come together for only a few weeks of each year. This phenomenon of splitting and merging for a defined purpose is known as “fission-fusion,” and Geoffroy’s spider monkeys inhabit fission-fusion societies.
Geoffroy’s spider monkeys forage over large tracts of forest in search of food. Home ranges for groups can exceed 2,200 acres (900 hectares), and the monkeys can cover 6,600 ft (2,000 metres) each day.
Geoffroy’s monkeys use a repertoire of sounds and postures to communicate. “Barks” are alarm calls used to signify a threat, while whinnies and screams are distress calls often made when separated from one another. Whinnies are perhaps the most versatile vocalization, also used to alert others in the group to a food source, to maintain contact with one another while foraging, and to call out at dawn and dusk. Because each monkey emits a unique sound, other monkeys in the group are able to recognize one another through vocal communication.
Postures include a curled tail or arched back, used as a threat display towards other spider monkeys. A head shake is used either as a threat or an invitation to play. Shaking branches or swaying arms are used to warn the group of impending danger. As an example, when approached by humans, Geoffroy’s spider monkeys bark, throw branches, shake tree limbs, and jump up and down.
The Geoffroy’s spider monkey has no specific breeding season; however, the ritual of copulation is defined and conducted with a modicum of decorum. After selecting her partner (mating is not restricted to dominant individuals, but dominant males mate more often than low-ranking males), the couple is given its privacy. Prior to mating, the male and female both separate themselves from others in their group. Copulation occurs with each in a sitting position facing the same direction, with the male seated behind. He wraps his arms around the female’s chest and his legs around her waist in an embrace that lasts from 8 to 22 minutes.
Females give birth to a single infant every two to four years, after a gestation period of seven to eight months. Babies are carried on their mothers’ chests for the first two months, and then begin riding on their mothers’ backs. They remain dependent on their mothers for three years.
As the youngsters begin moving independently through the forest canopy, they are often given a bit of assistance from adults in the group. Because the youngsters’ limbs aren’t yet long enough to propel them from tree to tree, an adult will stretch her body between two trees, forming a bridge so that these young Geoffroy’s spider monkeys can cross.
Females reach sexual maturity at four years, upon which time they typically leave their natal (birth) group and find another group to join. Males reach sexual maturity at five years and remain in their natal group.
Like all forest-dwelling primates, Geoffroy’s spider monkeys play an important role as seed dispersers. Foraging activity also stimulates the growth of trees, since extra foliage, branches, and other organic matter that is dropped from the canopy provides nutrients to the soil. Their feces are rich in nitrogen and phosphorus as well.
Geoffroy’s spider monkeys are classified as Endangered by the International Union of Conservation of Nature (IUCN, 2020), appearing on the IUCN Red List of Threatened Species. The species is listed as one of the world’s 25 most endangered primates in the 2018-2020 Primates in Peril report published by the International Union for Conservation of Nature along with the International Primatological Society and Conservation International.
Endangered means that the species faces a very high risk of extinction in the wild in the near future.
Habitat loss through deforestation (clear-cutting and transforming forests into agricultural fields) is the biggest threat to the survival of Geoffroy’s spider monkeys. The monkeys require large tracts of land to survive. Over the past 45 years (three generations), their population has suffered a 50-percent decline.
Geoffroy’s spider monkeys are also hunted for food and captured for the pet trade throughout Central America. They are relatively easy to find due to the chatter they make while in their large groups. As a result, the species has become locally extinct in most areas that are accessible to humans.
International trade of this species is prohibited by 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.
The Geoffroy’s spider monkey is included in the Species Survival Plan®, a cooperative breeding program between zoos working together to ensure the survival of the species.
However, additional conservation efforts are needed within the monkey’s natural habitat (in situ) to ensure the species’ long-term survival in the wild.
Written by Kathy Downey, August 2017