Spider monkeys are members of the order Primates, formerly included in the family Cebidae but now placed in the family Atelidae. They belong to the genus Ateles, which includes four species. These New World monkeys are found throughout the tropical rain forest regions of southern Mexico and Central and South America. Spider monkeys range between 14-26 inches in length and have an average weight of about 15-22 pounds. They are slightly potbellied and have coarse hair that varies from beige to deep black. Spider monkeys exhibit sexual monomorphism; males and females are almost identical in size and color.
Spider monkeys have narrow hands with long, curved fingers that function as hooks to firmly grasp tree branches, and most species lack an external thumb. They have extremely diverse locomotor abilities including arboreal quadrupedalism, suspensory behavior, and some bipedalism in the trees. A combination of long, lean appendages and exceptional agility assists them in making swift, acrobatic movements across the upper level of the canopy. Spider monkeys have a prehensile tail stretching from 24-36 inches that plays an important role in their arboreal lifestyle. The tail serves as a fifth limb as spider monkeys cross forest gaps up to 40 feet in length, sprawling out like spiders as they travel throughout the forest.
The social structure of spider monkeys is complex and generally referred to as fission-fusion. Spider monkeys form community units made up of approximately 15-25 members comprised of both sexes and a variety of ages. Females normally take on a more active leadership role than males, directing group activities such as traveling, foraging, and feeding. Although the spider monkey diet consists of an assortment of foods (leaves, nuts, seeds, flowers, insect larvae, and birds’ eggs), ripe fruit is the main staple. However, because ripe fruits are an ephemeral resource in both space and time, spider monkeys split up into smaller foraging parties of two to eight individuals in order to reduce feeding competition among group members. The dominant females usually have feeding routes that increase their foraging and feeding efficiency.
The spider monkey gestation period lasts close to eight months, at the end of which there is a single birth. Infant spider monkeys have a long period of dependence, and the strongest social bonds are formed between mothers and offspring. Not only do newly born spider monkeys remain black and nearly hairless for almost one year, but their mothers continue to carry and provide milk for them until they are around two years of age. Spider monkeys stay close to, and do not attempt to travel independently of, their mothers until around age three. Females become sexually mature between the ages of four and five, while males do not reach full sexual maturity until after their fifth year of life. Unlike many other primates, grooming is not of great importance in spider monkey social interactions. This may be due to their lack of functional thumbs.
With half of the Ateles species being endangered, research continues in order to determine the reasons that they are at risk of extinction, as well as to assess what can be done to prevent further harm. In the Central American countries of Costa Rica, Nicaragua, and Panama, farming is a major contributing factor to the spider monkey’s demise as vital habitat is lost to land cultivation. In addition, illegal hunting is also problematic. Spider monkeys have become an easy and attractive target, especially since they are relatively large and have a rather tame demeanor.
References:
- Fleagle, J. G. (1999). Primate adaptation and evolution. San Diego: Academic Press.
- Kinzey, W. G. (1997). New world primates: Ecology, evolution & behavior. New York: Walter de Gruyter.
