The Macaca fascicularis, widely recognized as the long-tailed macaque or crab-eating macaque, is an Old World monkey species. This primate is widespread across Southeast Asia, spanning countries such as Indonesia, Malaysia, the Philippines, and Thailand. They are also found in other regions globally, where human activity has introduced them. The species is characterized by its adaptable nature and a slender build.
Physical Traits and Natural Home
Their body fur typically ranges from grey-brown to reddish-brown, often appearing paler on their underside. The face is usually brownish-grey, framed by cheek whiskers, with males often displaying mustaches and females having fuller beards as they age. Their forward-directed eyes provide binocular vision, and their nose is flat with narrow, close-set nostrils. They also have shovel-shaped incisors, prominent canines, and bilophodont molars.
Males are generally larger than females, with adult males weighing between 4.8 to 7 kg and measuring 40 to 47 cm in body length, excluding the tail. Females are slightly smaller, weighing 3 to 4 kg with a body length of 40 to 47 cm. A defining characteristic, which gives them their common name, is their remarkably long tail, which can be greyish-brown or reddish and measures 50 to 60 cm, often exceeding their head and body length. This tail assists in balance, particularly when navigating arboreal environments.
The Macaca fascicularis is found throughout Southeast Asia, from Myanmar to the Philippines, and southward across Indochina, Malaysia, and Indonesia, reaching as far east as the Timor Islands. This species inhabits a wide array of environments, including:
- Primary and secondary forests
- Coastal areas, mixed mangrove swamps, and freshwater swamps
- Scrub grasslands and evergreen forests
- Human-modified landscapes like plantations and urban settings
Their population densities can vary considerably, from 10 to 400 individuals per square kilometer, often thriving in disturbed habitats or at the periphery of forests.
Daily Life and Social Habits
Long-tailed macaques are opportunistic omnivores. While they are known as “crab-eating macaques,” crabs do not constitute the primary part of their diet; instead, fruits and seeds make up 60% to 90% of their consumption. They also consume leaves, flowers, fungi, insects, bird eggs, and small vertebrates. Some coastal populations have been observed foraging for crabs, shellfish, and other aquatic life, even using stones as tools to crack open oysters and crabs. This tool use involves smashing shells with stones held in one or both hands.
These macaques live in multi-male/multi-female social groups, typically ranging from 10 to 85 individuals, though group sizes often fall between 35 and 50. Group size can be influenced by factors like predator presence and food availability. A strong dominance hierarchy exists within these groups, with alpha males typically having priority access to resources like food and mates. Lower-ranking individuals may display submissive signals to avoid conflict.
Communication among long-tailed macaques involves vocalizations, facial expressions, and body gestures. Affiliative vocalizations help maintain group cohesion and are used when approaching higher-ranked animals or infants. Facial expressions, involving movements of the ears, brow, eyes, and mouth, convey intentions and emotional states. Grooming is a significant social activity, contributing to relaxation and social bonding within the troop. These macaques spend a substantial portion of their day moving (18–30%), feeding (16–24%), and resting (16–20%).
Ecological Impact and Status
Macaca fascicularis contributes to seed dispersal in its native ecosystems. While they may not ingest many seeds, their cheek pouches allow them to carry seeds some distance from the parent plant before discarding them, contributing to plant propagation. They can also influence insect populations through their predatory habits. In areas where larger seed dispersers are absent, macaques can become important for distributing large, seeded fruits.
Despite their adaptability, the Macaca fascicularis has been classified as Endangered on the IUCN Red List of Threatened Species since March 2022. This status reflects a suspected population decline of at least 40% over the past three generations (approximately 40 years), with increasing rates of decline projected to reach 50% in the coming three generations. Major threats include habitat loss due to deforestation and conversion for plantations, as well as persecution from human-wildlife conflict. The species is also heavily impacted by trade for biomedical research, pets, and entertainment, with demand and prices significantly increasing.
In some non-native areas, Macaca fascicularis has become an invasive species. In these introduced environments, they can negatively affect native biodiversity by consuming native plants, competing with birds for fruit and seed resources, and aiding the dispersal of exotic plant seeds. They can also damage agricultural crops and may carry diseases transmissible to humans, such as B-virus. Additionally, Macaca fascicularis is widely used in scientific research due to their physiological similarities to humans.