The Barro Colorado Island spider monkey species is Ateles geoffroyi, the black-handed spider monkey. This species is covered with brilliant reddish hair, but the immediate facial area tends to be naked and the area around the eyes lightly pigmented, often with many tiny or large freckles or black dots. It is possible for human observers to recognize individual spider monkeys by their distinctive facial markings. When Barro Colorado Island was established as a nature preserve in 1924, there were no spider monkeys on the island as they had been exterminated from the area by hunters. In the late 1950's a number of young spider monkeys were purchased in the market in Panama City and released onto the island, provisioned with fruits to help them survive to adulthood.
Spider monkeys have an unusual social structure.
The entire group may come together late in the day, and, on BCI, are often all seen playing, grooming, or fighting around the laboratory buildings in the early evening but most of the day they are seen in small sub-groups of only a few individuals or even alone. Spider monkeys are dietary specialists in that the great majority of their food is ripe fruits. In this way, competition for ripe fruits should be kept low and all members of the community should get enough to eat. As fruiting trees tend to be fairly sparsely distributed throughout the forest, spider monkeys have a large home range. On BCI, it is estimated that male spider monkeys range over an area of 300 or more hectares in search of food while females range over a somewhat smaller area, estimated at 200 or more hectares.