1. Spider monkeys get their name from their spider-like appearance when they hang by their tails from the bow of a tree. The prehensile tail is so strong and well-developed for arboreal life that it can be used as an extra arm. The tail even lacks hair on the underside so that the monkey can get a better grip on a branch while using both hands to gather fruit.
2. Spider monkeys don't have thumbs on their hands. According to the Los Angeles Zoo, "The spider monkey’s genus refers to its absent thumb; in Greek ateles means 'not complete'." In reality, though, the spider monkey is simply more specialized and the thumb has evolved away because it isn't needed. Their hands have only vestigial thumbs, the tiny nub left over from their ancestors, who did have thumbs. The absence of this extra digit gives the spider monkey a more hook-like hand with long slender fingers, providing a better grip to swing from branch to branch in its arboreal abode. Spider monkeys do have opposable thumbs on their feet, like most other primate species.
3. Spider monkey troops are matriarchal, meaning the females play a leadership role. Females actively choose their mates when breeding, and tend to make the decisions for the group. Wildlife Waystation notes that even the group size is ultimately determined by the alpha female of the troop.
4. Rather than leap from tree to tree, spider monkeys are specialists at swinging from limb to limb, and can clear great distances in a single swing. Spider monkeys can cover as much as 40 feet of distance with a single powerful swoosh of their arms. The hook-like hands discussed above, as well as extra mobile shoulder joints assist spider monkeys with their impressive moves.
5. There are seven species of spider monkey, all of which are under threat of extinction. Two species — the black-headed spider monkey and brown spider monkey — are critically endangered. The Geoffroy’s spider monkey, pictured here, is found in Costa Rica and Nicaragua, and is currently listed as Endangered with habitat loss as the main threat to its survival.
The Geoffroy's spider monkey mother and infant pictured above was photographed at Bosque del Cabo, an eco-lodge in the Osa peninsula of Costa Rica. Once a cattle ranch, the lodge has been buying land and working to restore it to a natural state over the last 30 years, recreating the habitat once lost to agriculture and providing native species with food and shelter.