Crab-eating Macaque
The Crab-eating macaque (Macaca fascicularis) is a cercopithecine primate native to Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

. It is also called the "long-tailed macaque", and is referred to as the "cynomolgus monkey" in laboratories.


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 Africa
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...

n language) word (kaku means 'monkey' in Fiot). Fascicularis is Latin for 'a small band or stripe'. 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.

This animal has several common names. It is often referred to as the long-tailed macaque because its tail 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 because they are often seen foraging beach
A beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...

es for crabs. Another common name for M. fascicularis is the cynomolgus monkey, which literally means "dog-milker" monkey; this is the name most commonly used in laboratory settings. In Indonesia, M. fascicularis and other macaque species are known generically 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; it is classified into at least ten subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

  • crab-eating macaque, Macaca fascicularis fascicularis, synonym Macaca irus
  • Burmese long-tailed macaque, Macaca fascicularis aurea
  • Nicobar long-tailed macaque
    Nicobar Long-tailed Macaque
    The Nicobar long-tailed macaque is a subspecies of the crab-eating macaque , endemic to the Nicobar Islands in the Bay of Bengal...

    , 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
    Philippine Long-tailed Macaque
    The Philippine long-tailed macaque is a subspecies of the crab-eating macaque. It is found in most Philippine forests and woodlands, but especially in the mangrove forests of western central Philippines— particularly in Palawan, the Visayas, and Mindanao. The names M. f. philippinensis or...

    , Macaca fascicularis philippensis

Physical characteristics

Depending on subspecies, 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.

Social structure

Macaca fascicularis is a very social animal that lives in groups of 5–60 or more animals. These are multi-male groups, normally containing 2–5 males and 2–3 times as many females. The number of immature is usually comparable to the number of females. Group size
Group size measures
Many animals, including humans, tend to live in groups, herds, flocks, bands, packs, shoals, or colonies of conspecific individuals. The size of these groups, as expressed by the number of participant individuals, is an important aspect of their social environment...

 often depends on the level of predation and availability of food. Groups are female-centred, as the females are philopatric (i.e. remain in one place across generations), while 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 are defeated from time to time and then lose rank. High-ranked males are generally the most successful at reproduction and high-ranked females generally fare best at raising surviving offspring. The females are organized into matrilines
Matrilineality is a system in which descent is traced through the mother and maternal ancestors. Matrilineality is also a societal system in which one belongs to one's matriline or mother's lineage, which can involve the inheritance of property and/or titles.A matriline is a line of descent from a...

, which are the female-based families consisting of the related females and their descendents. Matrilines are ranked and some families have greater social power than others; 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 (12.3 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. Immigrant males will sometimes kill infants not their own, and high-ranked females sometimes kidnap the infants of lower-rank females. These kidnappings usually result in the death of the infants, as the other female is usually not lactating. Young juveniles stay mainly with the mother and relatives, 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 they leave their natal group. Males that emigrate with a partner seem 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.

Male crab-eating macaques will groom
Social grooming
In social animals, including humans, social grooming or allogrooming is an activity in which individuals in a group clean or maintain one another's body or appearance. It is a major social activity, and a means by which animals who live in proximity can bond and reinforce social structures, family...

 females in order to increase the chance of mating. A female is more likely to engage in sexual activity with a male that has recently groomed her than with one that has not.


Crab-eating macaques typically don't consume crabs; rather, they are opportunistic omnivore
Omnivores are species that eat both plants and animals as their primary food source...

s, eating a variety of animals, plants, and other materials. Although fruits and seeds make up 60 - 90% of the dietary intake, they also eat leaves, flowers, roots and bark. They also prey on vertebrates (including bird chicks, nesting female birds, lizards, frogs and fish), invertebrates and bird eggs. Although the species 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
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...


The crab-eating macaque can become a syanthrope, living off of human resources. The are known to feed in cultivated fields on such items as young dry rice, cassava leaves, rubber fruit, taro plants, coconuts, mangos and other crops, often causing significant losses to local farmers. In villages, towns, and cities, they frequently take food from garbage cans and refuse piles. The species can become unafraid of humans in these conditions, which can lead to macaques directly taking food from people, both passively and aggressively (9).

In Thailand and Myanmar, long-tailed macaques use stone tools to open nuts, oysters, other bivalves, and various types of sea snails (nerites, muricids, trochids, etc) along the Andaman sea coast and offshore islands.

Distribution and habitat

The crab-eating macaque is found in a wide variety of habitats, including primary lowland rainforest
Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...

s, disturbed and secondary rainforest
Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...

s, and riverine and coastal forests of nipa palm and mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...

. They also easily adjust to human settlements; they are considered sacred at some Hindu temples and on some small islands, but a pest around farms and villages. Typically they prefer disturbed habitats and forest periphery. The native range of this species includes most of mainland Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

, and the Maritime Southeast Asia
Maritime Southeast Asia
Maritime Southeast Asia refers to the maritime region of Southeast Asia as opposed to mainland Southeast Asia and includes the modern countries of Indonesia, Malaysia, the Philippines, Brunei, East Timor and Singapore....

 islands of Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...

, Java, and Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

, offshore islands, the islands of the Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

, and the Nicobar Islands
Nicobar Islands
The Nicobar Islands are an archipelagic island chain in the eastern Indian Ocean...

 in the Bay of Bengal
Bay of Bengal
The Bay of Bengal , the largest bay in the world, forms the northeastern part of the Indian Ocean. It resembles a triangle in shape, and is bordered mostly by the Eastern Coast of India, southern coast of Bangladesh and Sri Lanka to the west and Burma and the Andaman and Nicobar Islands to the...


Macaca fascicularis is an introduced alien species in several locations, including Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...

, western New Guinea
Western New Guinea
West Papua informally refers to the Indonesian western half of the island of New Guinea and other smaller islands to its west. The region is officially administered as two provinces: Papua and West Papua. The eastern half of New Guinea is Papua New Guinea.The population of approximately 3 million...

, Anggaur Island in Palau
Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a...

, and Mauritius
Mauritius , officially the Republic of Mauritius is an island nation off the southeast coast of the African continent in the southwest Indian Ocean, about east of Madagascar...

. Where it is a 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
World Conservation Union
The International Union for Conservation of Nature and Natural Resources is an international organization dedicated to finding "pragmatic solutions to our most pressing environment and development challenges." The organization publishes the IUCN Red List, compiling information from a network of...

 (IUCN) to list M. fascicularis as one of the "100 worst invasive alien species". Insofar as it is present as an invasive alien species on several islands, it has been labelled a "weed" species and is yet another significant ecological threat to those ecosystems and the species within them. However, M. fascicularis is not a biodiversity threat in its native range, where other species have adapted to their presence through evolutionary time.

Relationship with humans

Long-tailed macaques extensively overlap with humans across their range in SE Asia. Consequently, there are many locations where people and long-tailed macaques live together. Some of these areas are associated with religious sites and local customs, such as the temples of Bali in Indonesia, Thailand, and Cambodia, while other areas are characterized by conflict as a result of habitat loss and competition over food and space. Humans and long-tailed macaques have shared environments since prehistorical times, and tend to both frequent forest and river edge habitats (9).

Macaca fascicularis are also used extensively in medical experiments, in particular those connected with neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...

 and disease. Due to their close physiology, they can share infections with humans. Some cases of concern have been an isolated event of Ebola-Reston virus found in a captive bred population shipped to the US from the Philipines, which was later found to be a strain of Ebola that has no known pathological consequences in humans, unlike the African strains. Furthermore, they are a known carrier of Monkey B virus (Herpesvirus simiae), a virus which has produced disease in some lab workers working mainly with rhesus macaques (M. mulatta). Nafovanny
Nafovanny in Vietnam is the largest captive-breeding primate facility in the world, supplying long-tailed macaques to animal testing laboratories, including Huntingdon Life Sciences in the UK and Covance in Germany.-Background:...

, the largest facility for the captive breeding of non-human primates in the world, houses 30,000 macaques . The crab-eating macaque is one of the types of monkeys that have been used as space test flight animals
Monkeys in space
Before humans went into space, several animals were launched into space, including numerous monkeys, so that scientists could investigate the biological effects of space travel. The United States launched flights containing primate cargo primarily between 1948-1961 with one flight in 1969 and one...

 . It has been discovered recently that Plasmodium knowlesi
Plasmodium knowlesi
Plasmodium knowlesi is a primate malaria parasite commonly found in Southeast Asia. It causes malaria in long-tailed macaques , but it may also infect humans, either naturally or artificially....

, which causes malaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...

 in M. fascicularis, can also infect humans. There have been a few documented human cases, but we do not yet know for how long humans have been getting infections of this malarial strain. It is therefore not possible to assess if this is a newly emerging health threat, or if just newly discovered due to improved malarial detection techniques. Given the long history of humans and macaques living together in SE Asia, it is likely the latter.

Conservation status

The crab-eating macaque has the third largest range of any primate species, behind only humans and the Rhesus macaque
Rhesus Macaque
The Rhesus macaque , also called the Rhesus monkey, is one of the best-known species of Old World monkeys. It is listed as Least Concern in the IUCN Red List of Threatened Species in view of its wide distribution, presumed large population, and its tolerance of a broad range of habitats...

. The IUCN Red List categorizes the species as Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...

, and CITES lists them as Appendix II ("not necessarily threatened with extinction, in which trade must be controlled in order to avoid utilization incompatible with their survival"). A recent review of their populations suggests that there is need for better monitoring of populations due to increased wild trade and rising levels of human-macaque conflict, which are reducing overall population levels despite the species being widely distributed.

Each subspecies faces differing levels of threats, or simply lacks sufficient information to assess their situation. 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. is listed as near threatened, and M.f. condorensis is vulnerable. All other subspecies are listed as data deficient and need further study, although recent work is showing M.f aurea and M.f. karimondjawae need increased protection (9.) One concern for conservation is that in areas where M. fascicularis is non-native, their populations need to be monitored and managed to reduce impact on native flora/fauna (9).

External links

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