Squirrel monkeys are omnivores, eating primarily fruits and insects. Occasionally they also eat seeds, leaves, flowers, buds, nuts, eggs and small vertebrates.
Squirrel monkeys grow to 25 to 35 cm, plus a 35 to 42 cm tail. Male squirrel monkeys weigh 750 to 1100 g. Females weigh 500 to 750 g.
The Common Squirrel Monkey S. sciureus is captured for the pet trade and for medical research but it is not threatened. Two squirrel monkey species are threatened: S. oerstedti and S. vanzolinii are listed as Vulnerable by the IUCN.