The Crab-Eating Macaque
The Global Invasive Species Database lists 100 of those organisms which are recognised on a global level as a major threat to biodiversity, and to agriculture and other human interests. The introduction to the database acknowledges that it is difficult to choose 100 that are ‘the worst’.
Two criteria were observed when assembling the list. One was the impact on biological diversity and/or human activities, and the second was their illustration of important issues that arise when there is a biological invasion. There are a number of plants, insects, parasites and other organisms that are included in the list. The domestic cat, rabbit, red fox, muntjac deer, cane toad and bush rat are all on the list.
Another species that is on the list is the crab-eating macaque or long-tailed macaque (Macaca fascicularis). This Old World primate is native to Southeast Asia. It is often used in research laboratories where it is usually known as the cynomolgus monkey.
Macaques have few natural enemies in introduced ranges and impact on the environment by consuming native plants and competing with native fauna for fruit and seed resources. They may also eat out native flora species and contribute to the dispersal of seeds of exotic plants.
The crab-eating or long-tailed macaque’s common names come from its habit of foraging on beaches for crabs (although crabs form a very small part of its diet) and its long tail. It is the only macaque to have such a long tail.
There are at least ten subspecies, most of them named for the area which they inhabit. The macaque has the third largest range of any primates, surpassed only by humans and rhesus macaques.
Their native range includes mainland Southeast Asia, Sumatra, Borneo, Java, offshore islands and the Philippines and Nicobar Islands. It is a documented threat to island ecosystems to which it has been introduced such as Hong Kong, western New Guinea and Mauritius.
A wide variety of habitats is enjoyed by the macaque from primary and secondary lowland rainforests to riverine and coasts and mangrove swamps. They adjust easily to human settlements. While considered sacred at some Hindu temples, they are a problem on farms and in villages. Their preference is for living on the edges of forests. They divide their time between the trees and foraging on the ground. A large factor in their continued survival is their ability to ‘co-habit’ with humans.
Macaques and humans have a long history of sharing environments with both inclined to frequent forest and river edge habitats.
The length of the macaque varies from 38 to 55 cm. The arms and legs are relatively short. The tail may be 40 to 65cm but is only slightly prehensile and is mainly used for balance. Males are much larger than females weighing between 5 and 9 kg compared to 3 to 6 kg for females.
Macaques have cheek pouches which they use to store food for later and use their hands like most primates to help in eating and grooming.
The macaque lives in groups of 5 to 60+ animals. Females will outnumber males by two to three times. There will be a number of immature animals. Females stay in their groups while males come and go, generally leaving at age 4 to 6, staying in a new group for four or five years then moving on again. There is a strict hierarchy with males ranked higher than females. Fighting between rival males can become quite vicious with serious injury resulting.
Female-based families (matrilines) also have rank status with some families or ‘lines’ having greater social clout than others. Macaques have many facial expressions which they use for communication. On the Myanmar and Thailand coasts and offshore islands, the macaque uses stone tools to open nuts and shellfish.
Macaques are opportunistic omnivores. Fruits and seeds make up 60 to 90% of the diet. Flowers, leaves, roots, bark, nestlings, lizards, fish and frogs (and crabs!) are eaten. Invertebrates and eggs are also taken. It is this high adaptation to a very varied diet that can create problems if the macaque is introduced into an area where it is not native.
Macaques can also become accustomed to living off cultivated crops and can cause significant losses to local farmers. Many lose their fear of humans in villages and towns and become thieves, to the point of aggressively stealing food from humans.
Gestation takes 167 to 173 days and one infant is born, weighing about 350 grams at birth. The black fur of the babies gives way to the colour of their subspecies at about three months of age. Young males stay with the mothers for perhaps two years before being independent enough to find a new troop but young females will normally remain with its original troop for its life
Males will groom females to increase their chance of mating with that female. Dominant males have much more chance of mating and higher ranking females have much more chance of successfully raising their offspring.
The macaque shares a close physiology with humans and are used extensively in research and experiments, especially in the fields of neuroscience and disease research. Macaque monkeys are carriers of the monkey B virus. The parasite Plasmodium knowlesi causes malaria in the macaque and can also infect humans. This species has also been used as ‘guinea pigs’ in space test flights.
Almost all pet and captive macaques are carriers of the herpes B virus which is harmless to macaques but potentially life-threatening to humans. This makes the macaque unsuitable as a pet.
Although not threatened as a whole, the subspecies face differing levels of concern with some listed as ‘vulnerable’ or ‘near threatened’. All are data deficient and need further study. Rising levels of conflict with humans and increased illegal trading in the macaque are further cause for concern.
Macaques have few natural enemies. Large snakes, eagles and tigers will prey on macaques.
Although not in danger at the moment, habitat loss through deforestation and pollution is causing quite severe declines in the crab-eating macaque numbers.