Mammals
Spider Monkey
Ateles geoffroyi · also called Geoffroy's spider monkey, black-handed spider monkey
The spider monkey is the rainforest canopy’s acrobat — all limbs and tail, swinging arm over arm through the treetops with a grip so complete it barely needs to look down. Its tail is a fully working fifth hand, and it uses it constantly.
Overview
Spider monkeys live in tall, undisturbed rainforest from Mexico to western Colombia (Geoffroy’s spider monkey) and across the Amazon (other species). They are almost entirely arboreal, staying in the upper canopy and coming to the ground only rarely. They live in fission–fusion communities of 15–40 or more that split into small foraging subgroups by day and regroup to sleep — and unusually for a monkey, it is often the females that leave to join new groups.
Built for swinging
The spider monkey’s body is a brachiation machine:
- Long, slender arms and legs for reaching between branches
- Hook-like hands with the thumb reduced or gone — a simple, strong grip for fast swinging
- A prehensile tail that supports the monkey’s full weight and carries a hairless, ridged gripping pad near the tip, with its own nerve supply — a genuine fifth hand
A fruit specialist and forest planter
Ripe fruit is 70–90% of the diet. Because spider monkeys swallow large seeds and travel widely, they are major seed dispersers of big rainforest trees — forests that lose them lose the next generation of those trees.
Status
Geoffroy’s spider monkey is Endangered, down an estimated 50%+ in three generations. Spider monkeys are especially vulnerable because they need large intact forests, breed slowly (one baby every ~3 years), and are a preferred hunting target for their size, with infants taken for the pet trade.
Spider Monkey: common questions
How does the spider monkey's tail work?
It is a genuine fifth limb. The last third or so of a spider monkey's underside tail is hairless and covered in friction ridges, like the skin of a fingertip, and it even has its own touch-sensitive nerve supply and a groove that channels grip. The monkey can hang its entire body weight from the tail alone, use it to pick fruit or reach for a branch, and wrap it around a limb for security while it sleeps or feeds with both hands. Combined with its long arms and hook-like, thumbless hands, this lets the spider monkey move through the high canopy faster and more acrobatically than almost any other primate, swinging arm over arm and using the tail as a safety line.
Why doesn't the spider monkey have a thumb?
It traded the thumb for speed. Spider monkeys are committed brachiators — they travel by swinging hand-over-hand beneath branches — and for that a hand that closes into a simple, strong hook is more efficient than one with an opposable thumb getting in the way. The thumb is reduced to a small bump or missing entirely. They compensate for fine manipulation with the prehensile tail and by using the sides of the hand and the feet. Gibbons, the other great brachiators, have kept a thumb but set it far back and deep in the palm for the same reason.
Are spider monkeys endangered?
Geoffroy's spider monkey is listed as Endangered, and several of the seven spider monkey species are Endangered or Critically Endangered. They are among the most vulnerable Neotropical monkeys because they combine three bad traits — they need large tracts of tall, undisturbed forest with a year-round fruit supply, they reproduce very slowly (a female has one baby roughly every three years), and they are a favoured target for hunting because of their size. Forest clearance for cattle, agriculture, and roads fragments their habitat, and the pet trade takes infants after shooting the mothers. Populations have fallen by more than half in three generations.
How are spider monkeys different from howler monkeys?
They share the same forests but live very differently. Spider monkeys are lean, long-limbed, fast, and fruit-dependent, ranging widely each day through the high canopy in fluid subgroups. Howler monkeys are stockier, slower, leaf-eaters that can subsist on abundant foliage, move little, and live in stable cohesive troops — and the male howler's enlarged throat produces the roaring dawn chorus that carries for kilometres. Where spider monkeys vanish first when forest is disturbed, howlers can persist in smaller and more degraded fragments because their food is always available.