Wolly Monkey , either of two species of large monkey inhabiting the forests of the central and upper Amazon River basin. Humboldt's woolly monkey is yellowish-gray to blackish-brown, and the almost naked face is dark brown. The Peruvian mountain woolly monkey is mahogany, and its brown face has a brownish-yellow spot between its nose and upper lip; a yellow genital tuft occurs on the male. Both species have large heads; thick bodies with short, dense fur; protruding abdomens; and prehensile tails. They live in small troops of 4 to 70 individuals, often mixing with related monkeys such as capuchins, howlers, or spider monkeys. Moving slowly in the trees by day, they eat mostly fruit, which they supplement with leaves, seeds, and insects. They sometimes walk upright on the ground. A single young is born after a gestation of about five months .