Long-Tailed Macaque, Macaca fascicularis
LONG-TAILED MACAQUE
Macaca fascicularis
Geographic Distribution and Habitat
The long-tailed macaque, also known as the crab-eating macaque or the cynomolgus monkey, occurs sporadically throughout Southeast Asia. Though they once inhabited Bangladesh, they are now considered extinct, or extirpated, in that country. The northern limit of their distribution is difficult to determine due to interbreeding with the closely related rhesus macaque.
In Southeast Asia, these monkeys prefer coastal and lowland areas. They have been observed in the northern coastal region of Rakhine State in Myanmar, further south through the coastal lowlands of Myanmar, eastward into Thailand, and down into the Thai-Malay Peninsula. They are also found throughout most of Cambodia, the southeastern tip of Lao PDR, and southern Vietnam.
There are nine long-tailed macaque subspecies, with many being limited to specific islands or island groups; the island-restricted subspecies often occupy much smaller ranges and are more threatened than the mainland subspecies. These islands include all major island groups of the Philippines, the Nicobar Islands of India, and many Indonesian islands, including Borneo, Simeulue, Maratua, and the Karimunjawa Islands.
Humans have also introduced long-tailed macaques to areas outside their native range, including Mauritius, Palau, West Papua, Hong Kong, and Tinjil Island, Indonesia. Some of these introduced populations, like those in Hong Kong, have since been removed.
Long-tailed macaques are a highly adaptable species, living in a wide range of habitats: coastal forests, mangrove swamps, freshwater swamps, scrub grasslands, evergreen forests, bamboo forests, deciduous forests (forests with trees that lose their leaves seasonally), and even in or around human settlements like temples.
There are nine subspecies of the long-tailed macaque recognized by the IUCN Red List. The subspecies are primarily based on differences in geography and appearance, with most subspecies being found in isolated populations within specific regions. Their differences in appearance are minimal and usually involve fur color, tail length, and the shape or size of their whiskers. With that being said, the long-tailed macaque species as a whole is considered highly variable, meaning that even individuals within the same subspecies can still look quite different from each other.
The taxonomy of this species is complicated by its tendency to hybridize with other macaque species. As noted above, long-tailed macaques at the northernmost extent of their range often hybridize with rhesus macaques, and hybridization has also been documented with the southern pig-tailed macaque. In addition, gene flow between different subspecies of the long-tailed macaque is common, further blurring taxonomic boundaries.
Size, Weight, and Lifespan
As a highly variable species with multiple subspecies, long-tailed macaques exhibit a wide range of body sizes across individuals and between populations. In general, males have a head-body length of 16 to 25 inches (41 to 65 cm) and weigh around 10 to 18 pounds (4.5 to 8 kg). Females are slightly smaller, with a head-body length of 15 to 19.5 inches (38.5 to 50 cm) and a weight range of 5.5 to 12.5 pounds (2.5 to 5.5 kg). Studies comparing different populations found that their size changes from region to region. For example, long-tailed macaques from Singapore are smaller than those from Thailand. That being said, the Singapore macaques often have longer tails relative to their body length.
As their name implies, these animals are defined by their lengthy tails, which aid in balance and agility. Their tail lengths typically range from 12 to 28 inches (30 to 70 cm), with these tails almost always being longer than their head and body length.
In the wild, long-tailed macaques typically live between 15 and 30 years. Under rare, highly managed captive conditions—such as in well-resourced, professionally run institutions—some individuals have lived up to ten years longer, reflecting the species’ biological potential rather than a general benefit of captivity.
Appearance
Of the macaque species, the long-tailed macaque is on the smaller side. As their name suggests, their tails are very long and usually exceed the length of their bodies. Though the long-tailed macaque has many subspecies with slightly different fur patterns, their general coloring is brown to gray along the back, a lighter underside, and faces marked with black and white patterns, including white eyelids and pale patches near the ears. When observed from a closer distance, it becomes apparent that their fur is speckled, with some individual hairs ranging in colors like yellow, golden brown, reddish, white, and black. Their skin color can also vary—ranging from white to pink, brown, or even black—and often darkens with exposure to sunlight. Adults often have beards or whiskers, with older females sporting fuller facial hair and males having longer, whisker-like strands. Another notable facial feature is the cheek crest, which may run vertically or horizontally depending on the subspecies.
Like all macaque species, crab-eating macaques possess a unique suite of anatomical features adapted to living in a variety of environments. Macaques are quadrupedal, meaning they move on all fours, and their arms are slightly shorter than their legs to aid in this type of movement. Like all macaques, they are equipped with their own seats for sitting upright when resting. Known as ischial callosities, these rough pads of skin allow macaques to comfortably sit on their bottoms for long periods. Finally, long-tailed macaques have large cheek pouches in their mouths to store food. This is an incredibly useful adaptation seen in a variety of Afro-Eurasian primates that allows them to store and later consume a food resource away from potentially dangerous predators or other hungry macaques. Though there is considerable variation in body size and coat color, all long-tailed macaques possess this anatomical suite of traits.
Diet
Fruits, like bananas, papaya, and mangoes, make up a majority of the long-tailed macaque’s menu, though its diet can vary widely based on food availability, habitat type, and season. This dietary flexibility helps contribute to their ability to survive in a wide range of environments. They also eat flowers, young and mature leaves, small amounts of bark, and sometimes invertebrates, insects, and small animals. One study found that more than 60% of their diet came from just five plant species, even though the observed populations were recorded eating over 30 plant species in total, highlighting their ability to eat a wide range of foods while still having selective preferences.
Another study investigated the nutritional content of 12 fruit species commonly eaten by long-tailed macaques, finding fiber, a type of carbohydrate, as the most abundant nutrient overall. Other important nutrients included protein, fat, and various minerals.
A unique habit of these macaques is that they typically do not swallow large seeds. Instead, they choose to chew their fruit one at a time, storing the flesh in their cheek pockets, and spitting out any seeds. Other unique feeding behaviors of this species include catching and eating fish at coastal sites in Indonesia. They also use stones as tools to crack open oysters and crabs to access meat, which is where they got the nickname “crab-eating macaque.”
Long-tailed macaques that live in or around human-dominated landscapes often exhibit an altered diet as a result. This primarily includes the addition of food waste from garbage cans, as well as food provided by humans. One study found that human food waste made up more than one-quarter of the diet of long-tailed macaques living in these areas. This type of food lacks vital nutrients and often leads to human–macaque conflict. Furthermore, a study found that groups that had access to human-related food spent less time foraging for and eating wild fruits and flowers, in turn affecting their movement patterns and habitat use. Understanding how these macaques adapt to living in these environments is critical to a peaceful coexistence between humans and our surroundings.
Behavior and Lifestyle
The behavior and lifestyle of long-tailed macaques can vary depending on the type of habitat they live in, though their daily activity patterns are generally comparable. Moving and traveling take up about 18 to 30% of their day, while feeding accounts for 16 to 24% and resting for about 16 to 20%. A very gregarious species, they also spend considerable time socializing through grooming, playing, and sometimes mating behaviors, though time spent monitoring humans reduces the amount of social interaction for groups living around human settlements. These groups are also more sedentary despite having larger home ranges.
Long-tailed macaques are primarily arboreal, spending a majority of their time in trees, though it isn’t uncommon for them to walk along the ground when foraging or moving around. Most movement is done on all four limbs, including climbing vertically along branches. The average home range for groups is around 0.58 square miles (1.25 square kilometers), and though their daily travel distance varies widely, it is about 0.09 to 1.18 miles (150 to 1,900 meters). This movement most commonly takes place along riverbanks, which these macaques likely prefer due to the availability of preferred food items. Also, being excellent swimmers, staying by water is ideal to help these monkeys remain protected from predators. If threatened, they can escape by jumping into the water and swimming away. Though not a predator, silvered leaf monkeys have been known to be aggressive toward long-tailed macaques in overlapping habitats.
There are 9 subspecies of the long-tailed macaques.
Group sizes for this species can grow to as large as 100 members.
These monkeys use stone tools to break into oysters and crabs, which is how they got their nickname ‘the crab-eating macaque’! Only a select number of non-human primate species are known to use tools in the wild. More research is needed to understand which species use tools besides these macaques, capuchin monkeys, and our closest ape cousins.
Long-tailed macaques are active during the day, typically waking shortly before sunrise, around 5:30 to 6:00 a.m. Mornings are spent foraging for food, often in the company of group members who may compete for access to favored fruits. As temperatures rise toward midday, activity slows, and individuals rest in shaded areas, where social behaviors such as grooming are common. Juveniles frequently engage in play during these quieter hours. In the late afternoon, foraging resumes as the group gradually moves toward a riverside or forest-edge sleeping site. As night falls, group members settle close together, a strategy that offers warmth and protection from predators before the cycle begins again the next day.
Long-tailed macaques are highly social and live in large groups that can range from 20 to 100 individuals. Groups consist of multiple adult males and females, though there are usually more adult females. Females always remain in the group they are born into, with organized groups of closely related females determining dominance hierarchies. Males, on the other hand, tend to leave their birth group once they reach sexual maturity, sometimes changing groups multiple times in their lives. Younger males often band together in attempts to enter new groups at a higher rank, while older males typically migrate alone and accept entering their group at a lower rank.
The dominance hierarchy plays a strong role in long-tailed macaque group dynamics. The alpha male is, as you can guess, the most dominant, especially in fighting, eating, and receiving grooming. Both males and females exhibit very different behaviors within groups, in accordance with their rank. Higher-ranking males are typically more aggressive and are also more likely to initiate interactions with others in the group. Beta males often act as groomers but also take part in aggressive, attacking, and protective behaviors from time to time. High-ranking females exhibit aggression as well, typically with biting, and determine grooming dynamics, sexual behaviors, and infant care. Higher-ranking females also take priority when it comes to food distribution compared to lower-ranking females.
As would happen in any group-living situation, conflicts often arise among long-tailed macaque troops. Reconciliations are common afterward, usually initiated by the most dominant individual involved in the dispute; an individual will approach the other to groom, alleviating stress and effectively mending the situation.
Long-tailed macaques communicate in a variety of ways—including vocal sounds, facial expressions, and body gestures—with each serving a specific purpose. Vocal calls, often made in clusters, can mostly be summed up in two main categories: harsh and clear calls. Researchers have identified thirteen types of harsh calls, which are mostly used in high-stress situations. There is a “kra” call to signal an alarm during both mild and intense situations. They have another alarm call, three to five “chirps,” which is made specifically when a predator is seen or suspected to be approaching. Long-tailed macaques are also known to bark, usually during conflicts within the group. Clear calls are much more common and are used in friendly, loving interactions among groups. The most common clear call is a coo, which helps strengthen social bonds and reduces aggressive behaviors. Females are most likely to coo, as well as infants.
Other important vocalizations include screams, usually made by low-ranked individuals being attacked by dominant members; affiliation calls made by females when interacting with a female infant; and “gecker” sounds made by infants during conflicts or other stressful situations. Lastly, there are copulation calls made by adult females during mating activities.
Common facial expressions used by the long-tailed macaque include baring teeth to express submission or fear, lip smacking to initiate friendly interactions, and genital presentation to signal possible mating opportunities.
Long-tailed macaques breed year-round, but births often show seasonal peaks depending on location and food availability. Gestation, or pregnancy, lasts roughly six months, with females giving birth to a single infant. After birth, females usually avoid breeding for the next year in order to prioritize raising their infant.
Females reach sexual maturity at around four years old, with high-ranking females reproducing earlier than low-ranking ones, while males do not reach maturity until five to seven years old. Female reproductive ability peaks at around 10 years of age and begins to decline after age 20, with pregnancy typically no longer occurring after around age 24.
The alpha male usually fathers around 80% of the infants in a group, with beta males accounting for most of the remaining offspring. This dynamic is solidified through certain behaviors, including mate guarding. This is when the breeding male stays within 16.5 feet (5 m) of a fertile female and exhibits aggressive behaviors, effectively preventing other males from mating with her. This behavior is very labor-intensive, so it usually does not take place for more than a few days. Females signal their fertility visually with red sexual swellings on their rumps and by initiating mating behaviors, making copulation calls, grooming after intercourse, and potentially using scent cues. When mate guarding isn’t taking place, subordinate males can sometimes attempt to mate with females while a dominant male is distracted, but even these attempts are usually interrupted once the dominant male notices and physically interferes.
Female dominance hierarchies also play a pivotal role in mating dynamics, with high-ranking females reproducing earlier, having more offspring throughout their lifetime, and having higher survival rates among their offspring. Daughters usually inherit a similar dominance rank to their mother.
Females often mate multiple times a day while fertile, trying their best to mate with multiple males. They do this to reduce the risk of infanticide by increasing paternity uncertainty. When a new male takes over a group, he sometimes kills all the infants he believes are not his. Without infants to nurture, the females quickly become fertile again and, in turn, allow the new alpha male to spread his genes throughout the troop by fathering the next generation.
When young are born, birth mothers are very protective and generally take responsibility for all caregiving duties. Sometimes, other females attempt to interact with infants they did not give birth to, occasionally trying to take them away, which can lead to infant death. Mothers maintain constant contact with their infants during their first weeks of life. Weaning behaviors occur after a few months, with mothers completely cutting off nursing once their young reach around 10–11 months. Once young macaques reach the juvenile stage, adult males often begin interacting with them more frequently, usually through play. About 81% of infants survive their first year, with survival dropping to 68% by four years of age. The mother’s social rank heavily affects infant survival but has less impact on juvenile survival.
Since these macaques store seeds in their cheek pouches while traveling, they can help with seed dispersal throughout their environments. Eating insects and other small animals helps to maintain potential pest populations and ecological balance. They also serve as food for many predators, including tigers, eagles, crocodiles, snakes, and other large reptiles.
Long-tailed macaques are classified as Endangered by the International Union for Conservation of Nature (IUCN, 2024), appearing on the IUCN Red List of Threatened Species. The IUCN has also estimated a population decline of over 40% from 1984 to 2024, with decline rates increasing. One of the leading causes of this is hunting and trapping, with the long-tailed macaque being the most heavily traded primate species in the world. From 2010 to 2019, at least 163,780 individuals were traded from seven Southeast Asian countries. This number is even larger when including non-habitat countries, like China and Mauritius. Another study found that around 450,000 long-tailed macaques were imported internationally between 2008 and 2019, accounting for 90% of global legal primate trade. These jarring numbers do not include illegal trade, domestic trade, hunting, or culling.
Much of this international trade is done for biomedical and toxicology research. The USA, Japan, China, Canada, and the EU are all drivers of this multi-billion-dollar industry, but only Indonesia and China have submitted sustainability reports required by CITES, the Convention on International Trade in Endangered Species. This species was added to Appendix II of CITES, signifying that trade must be limited and controlled.
The pet and entertainment trades also plague this species. Since there are no known breeding programs, long-tailed macaques used for the pet or entertainment trade are wild-caught. Market surveys have revealed extremely high numbers of macaques being sold, including an estimated 10,000 to 20,000 individuals each year in Indonesia alone.
Habitat loss is another major contributor to the endangered status of this species, with over 50% of tree cover being lost in Cambodia, 18% in Indonesia, and 21% in Vietnam between 2002 and 2022. Mangrove forests, a preferred habitat of the species, have declined by around 20 to 35% globally since 1980. Destruction of these habitats, primarily done for shrimp farming, has led to the extinction of this species in Bangladesh. Environmental changes and deforestation across Southeast Asia are pushing macaques into urbanized spaces, where they may not survive long-term. Furthermore, macaques are unfairly labeled as pests in these areas, resulting in large-scale removals. Nearly 500,000 individuals were removed between 2011 and 2018 in Peninsular Malaysia alone.
Long-tailed macaques are listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments to ensure that international trade in specimens of wild animals and plants does not threaten their survival. This classification means that international trade can only be legally conducted with permits, strict monitoring, and in accordance with CITES-set quotas.
The species is considered to be protected in Cambodia, the Philippines, Myanmar, Vietnam, Malaysia, Singapore, and Thailand, though regulations and protection strength differ by law and region. In India, long-tailed macaques are listed under Schedule I of the Wildlife Protection Act, which provides them with the highest level of legal protection offered by the government. Under this classification, hunting is strictly prohibited, and severe penalties are imposed on anyone who violates the law.
The Long-Tailed Macaque Project champions this species by advancing scientific knowledge of its needs across South and Southeast Asia through field research, collaboration with local scientists, and raising conservation awareness. They have led a coexistence project in Penang, Malaysia, and a coconut plantation coexistence project on Simeulue Island, Indonesia, geared towards fostering camaraderie between humans and macaques. They have also supported population surveys, published scientific research, and formally challenged the long-tailed macaque’s IUCN Red List status to improve how the species is managed and protected.
Ultimately, much more work must be done to properly support this species, including the cultivation of more conservation programs. The lack thereof is partially due to long-tailed macaques historically being labeled as common or even overly abundant.
The IUCN, CITES, and the scientists comprising these reputable organizations are all lobbying for the same thing: more in-depth wildlife monitoring, accurate population surveys, protection and management programs, and better regulation of trade. Singapore is the only country that routinely conducts a census of its long-tailed macaque population. It is pivotal that the rest of South and Southeast Asia follow suit to properly manage legal and illegal trade. Human–macaque coexistence programs led by local experts are also necessary to reduce conflict in these shared spaces. More scientific research is needed to make these efforts possible and to identify additional ways to effectively support the survival of this species. Without these necessary changes being made, significant population declines are inevitable.
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Written by Hannah Broadland, Dec 2025