Genus: Ateles
Species: belzebuth (white-bellied or long-haired spider monkey), chamek (black-faced spider monkey), fusciceps (black-headed or brown-headed spider monkey), geoffroyi (black-handed or golden spider monkey), marginatus (white-whiskered spider monkey), and paniscus (black or red-faced spider monkey)

Habitat and Physical Characteristics:

Spider monkeys, among the most nimble of all primates, are found in tropical rainforests (usually in the top layers of the tree canopy) from southern Mexico to Mato Grosso in Brazil. Like all new world monkeys, they have a prehensile tail, prominent snout and widely separated nostrils. They are about 50 centimeters in length (not counting the 90-centimeter tail), weigh 6-11 kilos, and have long arms and legs, a small noggin and a bulging abdomen. They don't have opposable thumbs, but the tail, which is naked on its underside and ridged like a fingertip, is used as a fifth limb. They are also said to be able to balance their entire weight on the tip of the tail.

Eating:

Spider monkeys are generally frugivores, with about 80% of their diet consisting of fruits. However, they also eat flowers, leaves, seeds, nuts, insects and sometimes eggs. Because of their reliance on higher quality foods which are more dispersed (as compared with other new world monkeys), they have to cover more ground in a day and have more territory to defend. To facilitate their foraging habits and develop patterns of movement that help them avoid conflict, they have evolved a brain that is about twice as large as new world monkeys of similar size. In a pinch, they will open unripe fruit to accelerate its ripening, or even raid the dining areas of primatologists. In times of plenty, they intentionally leave some fruits on the vine to ferment, and set aside an evening for drunken revelry and tomfoolery. The next morning they can be seen huddling together and avoiding the sun.

Social Organization and Sexual Habits:

Spider monkeys arrange themselves into groups of about 10-40 on the median average, with some groups having as few as 3 members and others as many as 100. These are divided into extremely fluid subgroups of 8-15, and the full group comes together for only a few weeks out of the year. Generally, the more plentiful the food supplies, the more they will bunch together. Females are larger than males and outnumber them 2-1, but are more solitary. Males are more aggressive and form coalitions to assert dominance. However, when it comes to mating, it is the female who chooses her mates. She will sometimes stick with one partner, and at other times mate with several males in one day. Her estrus cycle is 24-27 days long, and she is fertile for 3-4 days during that time. Gestation periods range across the six species from 139-230 days, usually at the upper end of that continuum. Offspring are dependent on the mother for about 3 years, and reach sexual maturity around age 4 for females and 5 for males. Grooming is pretty much restricted to a mother and her young, because the lack of thumbs makes it a challenge. Females give birth every 2-4 years, and due to the slow cycle of reproduction, immature spider monkeys make up only about 30% of a group at any given time.

Due to the nature of their diet, territory is a complicated and ever-shifting thing, and is marked by secretions from the chest glands of dominant males. If one group enters the range of another, they will be greeted by a cacophony of screams, barks, and rattling branches, they will have branches and feces thrown at them; and they'll respond in kind. (You can hear what this sounds like at http://www.honoluluzoo.org/spider_monkey.htm.) The conflict rarely if ever comes to blows, but instead is decided by the relative size of each group. Spider monkeys generally share their range with other diurnal monkey species, but they've been known to hassle howlers and capuchins, sometimes kidnapping their young (who are thereafter only seen on milk cartons).

Status:

The white-bellied, brown-headed, and white-whiskered spider monkeys are listed as endangered, meaning they have a 20% of becoming extinct in the wild in the next 5 of their generations. The black-handed and black spider monkeys are listed as vulnerable, meaning a 10% chance of extinction within 25 generations, and the black-faced spider monkey is considered relatively safe. The main threats they face are disappearance of habitat (especially considering that they need such a large area), hunting, and black market trade.

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