The crab-eating macaque (Macaca fascicularis) is a primarily arboreal macaque native to Southeast Asia. It is also called the cynomolgus monkey and the long-tailed macaque.
It has been used extensively in medical experiments, in particular those connected with neuroscience. It has also been identified as a possible vector for monkey pox and is a known carrier of B-virus. It is one of the types of monkeys that have been flown into space.
The crab-eating macaque is found in a wide variety of habitats. These include primary lowland rainforests, disturbed and secondary rainforests, and riverine and coastal forests. They also easily adjust to human settlements and are considered sacred at some Hindu temples. Typically it prefers disturbed habitats and forest outer edge. The native range of this species includes most of mainland Southeast Asia. This includes the Malay Archipelago islands of Sumatra, Java, and Borneo. This also includes the islands of the Philippines, and the Nicobar Islands in the Bay of Bengal.
Its diet is not restricted to eating crabs. They are an opportunistic feeder omnivore. This means they can and will eat a wide variety of animals, plants, and other materials. Fruits and seeds make up 60 to 90% of the dietary intake. It also eats leaves, flowers, roots and bark. It also preys on vertebrates, invertebrates, and bird eggs.
It is a very social animal that lives in groups anywhere from 5 to 60 plus animals. These groups are multi-male groups, normally containing 2 to 5 males. There are two to three times more female. The number of immature is usually comparative to the number of females. Their group size often depends on the level of predation and availability of food. Their groups are female-centered, as the females remain in on place across generations. The males move in and out of these female-based groups. Males generally first immigrate from their natal group at the age of 4 to 6. They will remain in a group up to 4 or 5 years. They will emigrate several times throughout their life. These monkeys are highly oppressive and have a strict dominance hierarchy. Adult males rank higher than females. Female ranks are more stable than males, as males from time-to-time will be defeated and lose rank. High-ranked males generally are more successful at reproduction. High-ranked females are generally fared better at raising surviving offspring.
Infants are born with black fur. This fur will begin to turn to a yellow-green, grey-green, or reddish-brown shade (depending on the sub-species) after about 3 months of age. It is suggested this natal coat indicates to others the status of the infant. Other group members treat infants with care and rush to their defense when distressed. Newly immigrated males will sometimes steal infants not their own. High-ranked females sometimes kidnap the infants of lower-rank females. These kidnapping usually result in the fatality of the infants, as the other female usually is not lactating. Young juveniles stay with the mother and relatives.