Cynomolgus Monkey, Philippine Monkey or Long-tailed Macaque

The Crab-eating Macaque (Macaca fascicularis) is a primarily arboreal macaque native to Southeast Asia. It is also called the Cynomolgus Monkey, Philippine Monkey and the Long-tailed Macaque.


Crab-eating macaque eating ice-cream.

The scientific name of the Crab-eating Macaque is Macaca fascicularis. Macaca comes from the Portuguese word macaco, which was picked up from makaku, a Fiot (West African language) word (kaku means 'monkey' in Fiot). Fascicularis is Latin for 'a small band'. Sir Thomas Raffles, who gave the animal its scientific name in 1821, did not specify what he meant by the use of this word although it is presumed it had something to do with his observation of the animal's colour.

The common name of this animal varies. It is commonly referred to as the Long-tailed Macaque because the tail of this macaque is usually about the same length as its body and because its long tail distinguishes it from most other macaques. The species is also commonly known as the Crab-eating Macaque. Another common name for M. fascicularis is the Cynomolgous Monkey, which literally means "dog-milker" monkey, which is the name most commonly used for these animals in laboratory settings. In Indonesia, M. fascicularis and other macaque species are generically known as kera, possibly because of the high-pitched alarm calls they give when in danger ("krra! krra!").


There is significant genetic diversity within the species and these differences are classified into at least 10 subspecies:

* Crab-eating Macaque, Macaca fascicularis fascicularis
* Burmese Long-tailed Macaque, Macaca fascicularis aurea
* Nicobar Long-tailed Macaque, Macaca fascicularis umbrosa
* Dark-crowned Long-tailed Macaque, Macaca fascicularis atriceps
* Con Song Long-tailed Macaque, Macaca fascicularis condorensis
* Simeulue Long-tailed Macaque, Macaca fascicularis fusca
* Lasia Long-tailed Macaque, Macaca fascicularis lasiae
* Maratua Long-tailed Macaque, Macaca fascicularis tua
* Kemujan Long-tailed Macaque, Macaca fascicularis karimondjawae
* Philippine Long-tailed Macaque, Macaca fascicularis philippinensis

Physical characteristics

Depending on sub-species, the body length of the adult monkey is 38-55 centimetres (15-22 in) with comparably short arms and legs. The tail is longer than the body, typically 40-65 cm (16-26 in). Males are considerably larger than females, weighing 5-9 kilograms (11-20 lb) compared to the 3-6 kg (7-13 lb) of female individuals.

Macaca fascicularis is a very social animal that lives in groups anywhere from 5-60+ animals. These groups are multi-male groups, normally containing 2-5 males and 2-3 times as many females. 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-centred, as the females are philopatric (i.e. remain in one place across generations) and the males move in and out of these female-based groups. Males generally first emigrate from their natal group at the age of 4-6. They will remain in a group up to four or five years and thus will emigrate several times throughout their life. These monkeys are highly despotic 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 and high-ranked females generally fare better at raising surviving offspring. The females are organized into matrilines, which are the female-based families consisting of the resident females and their offspring. Matrilines are ranked and some families have greater social power than others and this difference in rank is maintained over several generations. Matrilineal overthrows rarely occur and when they do they have severe consequences to the reproductive success of the defeated matriline in the following year.

After a gestation period of 167-193 days, the female gives birth to one infant. The infant's weight at birth is approximately 350 grams (12 oz). Infants are born with black fur and this fur will begin to turn to a yellow-green, grey-green, or reddish-brown shade (depending on the sub-species) after about three months of age. It is suggested this natal coat indicates to others the status of the infant and other group members treat infants with care and rush to their defence when distressed. Newly immigrated males will sometimes commit infanticide on infants not their own, and 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 mainly, and as male juveniles get older they become more peripheral to the group. Here they play together forming crucial bonds that may help them when the emigrate from their natal group. Males that emigrate with a partner seems to be more successful than those that move off alone. Young females on the other hand stay in the centre of the group and become incorporated into the matriline they were born into.

Results of a research shows that male Crab-eating Macaques will groom females in order to get sex. The study found that a female has a greater likelihood to engage in sexual activity with a male if he had recently groomed her, compared to males who had not groomed her.


Although this species is often referred to as the Crab-eating Macaque, this name is something of a misnomer since its diet is by no means limited to crabs. Other food items are in fact far more common. They are an opportunistic omnivore, meaning they can and will eat a wide variety of animals, plants, and other materials. Although fruits and seeds make up 60 - 90% of the dietary intake, it also eats leaves, flowers, roots and bark. It also preys on vertebrates (including bird chicks and nesting female birds, lizards, frogs, fishes, et al.), invertebrates, and bird eggs. Although it is ecologically well-adapted in its native range and poses no particular threat to the overall populations of prey species, in areas where the Crab-eating Macaque is non-native it can pose a substantial threat to biodiversity.

The Crab-eating Macaque is sometimes known as a "crop-raider", feeding in cultivated fields on such items as young dry rice, cassava leaves, rubber fruit, taro plants, coconuts, mangos, and other crops, thus often causing significant losses to the cash incomes of local farmers. It also takes food from graveyards, garbage cans, and garbage pits. The species is often unafraid of humans, and is found in many cities and villages. It has been involved in aggressive interactions with people.

Distribution and habitat

Being "ecologically diverse", the Crab-eating Macaque is found in a wide variety of habitats, including primary lowland rainforests, disturbed and secondary rainforests, and riverine and coastal forests of nipa palm and mangrove. They also easily adjust to human settlements and are considered sacred at some Hindu temples and on some small islands, while a pest when around farms and villages. Typically it prefers disturbed habitats and forest periphery. The native range of this species includes most of mainland Southeast Asia, including the Malay Archipelago islands of Sumatra, Java, and Borneo, the islands of the Philippines, and the Nicobar Islands in the Bay of Bengal.

Macaca fascicularis is an introduced alien species in several locations, including Hong Kong, western New Guinea, Anggaur Island in Palau, and Mauritius. Where they are non-native species -- particularly on island ecosystems whose species often evolved in isolation from large predators -- M. fascicularis is a documented threat to many native species. This fact has led the World Conservation Union (IUCN) to list M. fascicularis as one of the "100 Worst Alien Invasive Species". Insofar as they are present as an alien invasive on several islands, they have been labelled a "weed" species and are yet another significant ecological threat to those ecosystems and the species within them. It is important to note, however, that M. fascicularis is not a biodiversity threat in their native range, as other species therein have adapted to their presence through evolutionary time.

Relationship with humans
Macaca fascicularis has been used extensively in medical experiments, in particular those connected with neuroscience. It has also been identified as a possible vector for Ebola virus, monkeypox and is a known carrier of B-virus (Herpesvirus simiae). Nafovanny is the largest captive-breeding non-human primate facility in the world, and houses 30,000 macaques. The Crab-eating Macaque is one of the types of monkeys that have been used as space testflight animals.

Conservation status

The Crab-eating Macaque has the third largest range of any primate species, behind only humans and the Rhesus Macaque. Since the wild harvest of the species for animal testing has been reduced by captive-breeding programs, the total population of M. fascicularis is not under significant threat. The IUCN Red List categorizes the species as "Lower Risk"; and CITES lists it as Appendix II ("not necessarily threatened with extinction, but in which trade must be controlled in order to avoid utilization incompatible with their survival". The umbrosa subspecies is argued to be of important biological significance. It has been recommended as a candidate for protection in the Nicobar islands, where its small, native population has been seriously fragmented (Umapathy et al., 2003). One main conservation concern is that in areas where M. fascicularis is non-native, their populations need to be monitored, managed, or eradicated where they have a negative impact on native flora/fauna.

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This webpage was updated 1st May 2020