Monkeys are omnivores, meaning they eat both plant materials and animals in the jungle; however, the diet of most species includes far more foods from plants than from animals. In the wild, baboons are observed occasionally eating meat, such as rabbit or even antelope, if they are able to catch the animals.
Monkeys use their tails to hold on while they collect their food. They are foragers who sometimes eat fruits and nuts if they are available but will also dine on leaves, seeds, spiders and bird's eggs. Old World monkeys have large cheek pouches that they fill as they forage throughout the day. They only stop to chew and swallow the food once they find a safe and comfortable place to rest.
Other species of monkeys, including the Colobus monkeys and langurs have stomachs with more than one chamber. Inside these chambers is bacteria that ferments the leaves, allowing the monkey to digest them. Geladas graze on grass, according to the San Diego Zoo.
Between 80 and 90 percent of the diet of the spider monkey is from plant materials. However, they supplement animal sources to meet their protein needs. These monkeys eat on the run. The spider monkey's diet moves through the digestive tract in about four hours.