VARIEGATED SPIDER MONKEY
Geographic Distribution and Habitat
The variegated spider monkey—also known as the brown spider monkey—is endemic to northern Colombia and northwestern Venezuela. They are an arboreal species that prefers the canopies of tall trees; they mostly opt for rainforest habitats, but riverine, marsh, and semi-deciduous forests also suit this species’ needs. Primary forests are best suited for the variegated spider monkey, since they offer more abundant canopies and fruit than disturbed forests. This species does well at elevations anywhere from 65 to 2,300 ft (20–700 m).
Size, Weight, and Lifespan
There is a small difference in size between the sexes in variegated spider monkeys. Males typically weigh 22 lb (10 kg), while females typically weigh 16 lb (7.3 kg). Males measure 18.5–19.5 in (47–50 cm) from head to body; females aren’t quite as long, measuring 17.7–18.9 in (45–48 cm). Tails range from 30 to 32 in (76–81 cm) for males, and 29–30 in (74–76 cm) for females. These long tails are critical to this species’ ability to move easily through the treetops. In the wild, variegated spider monkeys have reportedly lived to be as old as 27.
The name “spider” monkey is derived from the species’ long arms, legs, and tail that make this monkey’s proportions seem vaguely similar to those of an arachnid. “Variegated” refers to its discrete markings of different colors—the lightness of its belly, the darkness of its back, and the white patch of fur on its forehead.
The length of variegated spider monkeys’ front limbs is greater than that of their rear limbs. The coloration of this species varies greatly—from light tan, to a tawny color, to very dark brown, with their abdomens being a whitish gray color. Their heads are dark, save for that one blotch of white on their forehead.
One of the most arresting features of the variegated spider monkey is its long, prehensile tail. The tail features a hairless tip with grooved skin, allowing this species to wrap its tail around branches with a firm grip—it is often compared to a fifth limb. The hands of the monkey feature four very long fingers, too, which are hooked to serve a similar purpose as their tails.
The variegated spider monkey is a diurnal forager, with a preference for ripe fruit. They eat a lot of figs, and seek out food sources with high lipid content. When ripe fruit is not available, they will eat leaves, bark, flowers, honey, termites, and sometimes even decaying wood. When they descend from the treetops for water, variegated spider monkeys occasionally eat soil. This, some believe, could be to aid in digestion by helping the monkeys maintain a healthy pH.
Behavior and Lifestyle
Variegated spider monkeys typically travel by swinging from tree to tree, using their long limbs and tails to navigate deftly through the canopy. They are very social monkeys—though there are factors that dictate the size and dynamics of groups. When food is abundant, for example, groups are large, and the monkeys tend to spend more time together. When food is scarce, groups are smaller, and there is less interaction between individuals. All told, the typical range of a group of variegated spider monkeys is anywhere from 1 to 1.5 sq mi (260–390 ha). When it comes time for them to sleep, they find strategic sleeping areas near food sources, so they won’t have to travel too far to forage the following day.
Some variegated spider monkeys have pale blue eyes, which provide a vibrant contrast to their pelage.
These monkeys live in multi-male, multi-female groups of as few as three and as many as 22 individuals. There is no clear hierarchy within groups. During times of abundance, there is an increase in both females interacting with each other and males interacting with each another.
Their day is dominated by the search for food. To forage, the larger group segments into smaller groups. This is called a fission-fusion structure, meaning the group’s size changes as it tends to different tasks. When the larger group convenes, that’s fusion; when the group breaks up into small subgroups to forage, that’s fission. Primates other than spider monkeys that adopt this organization include baboons and chimpanzees.
Among the auditory communications recognized in this species are “whoops,” “chookis,” and “wails.” These are used primarily to help the large group reconvene after splitting up to forage. When they are reunited, there are auditory and tactile communications—notably, variegated spider monkeys will hug and wrap their tails together as a way to say hello after time spent apart.
The gestation period for this species is 225 days; infants are born one at a time, at intervals of every three to four years. Though not overtly seasonal, the birth rate is higher during the rainy season, which spans from May to July. Once an infant is born, it depends on its mother—first riding along holding on to her belly for about four months, then riding on her back until the child is capable of moving about of its own volition. Females take on the brunt of the parenting, and the relationships between mothers and their offspring are strong. The mothers look after their young while they learn basic skills, from how to interact within the group, to how to forage for food. After around four years, individuals reach sexual maturity, and females generally start reproducing at the age of seven or eight.
Due to the nature of its diet, the variegated spider monkey plays a role in two types of seed dispersal: endozoochory, when the animal distributes seeds after digesting them, and exozoochory, when the animal physically carries seeds on its body and spreads them throughout its habitat. Seed dispersal helps the forest remain healthy.
The variegated spider monkey is considered Critically Endangered by the International Union for Conservation of Nature (IUCN, 2020). Their population is decreasing; they are among the 25 most endangered primate species on the planet. Threats include: development of residential, commercial, and industrial areas around this species’ habitat; building of roads and railroads; continual practice of hunting, trapping, and logging; and farming and ranching. Within its wild range, variegated spider monkeys have already lost 98% of their habitat to these myriad threats. They also face threats from predators such as mountain lions, jaguars, and eagles. When faced with predators, variegated spider monkeys shake tree branches to fend them off.
According to the IUCN, there are measures being taken to conserve this species. As far as preserving its habitat, portions of this species’ range occur in protected areas. Even still, poachers often see protected areas as prime locations for poaching.
There are also programs in place to spread awareness of variegated spider monkeys and the various threats they face. Education, as with any conservation effort, is a critical component.
Written by James Freitas, January 2019