Before becoming accustomed to the newcomers, spider monkeys have occasionally broken off heavy tree limbs to drop on these suspicious intruders. Prefer the middle and upper canopy of the forests. Group size seems to fluctuate greatly. Associations of approximately 100 have been seen although typical group size is around 20 with subgroups of 2 - 8 individuals. One young is produced after a seven and a half month gestation.
Maturity is reached at ages four to five.
In addition, aggressive hunting as a food source has lead to their elimination in several areas. A great reference book on primates is Noel Rowe's The Pictorial Guide to the Living Primates . Dr. David Macdonald's Encyclopedia of Mammals is one of the great standards for mammal information including the monkeys.