Simias concolor

Geographic Distribution and Habitat

Endemic to Indonesia, the pig-tailed snub-nosed langur (also known by its less-pejorative nickname, the simakobu monkey) is found only on the archipelago of Mentawai off the western coast of Sumatra. Interspersed through the islands of Siberut, Sipora, North Pagai, and South Pagai, and through a few offshore islets, these monkeys make their homes on the hillsides of primary forests within the islands’ interior regions. Fresh-water and brackish-water swamp forests, mangrove forests, and lowland rainforests may provide alternative habitats.

The pig-tailed snub-nosed langur (Simias concolor) has the ignominious distinction of being named as one of the earth’s 25 most endangered primate species for 2017. Hunting has taken a grim toll on the population.

 Wildlife biologists acknowledge two subspecies:

  • S. c. concolor, found on the islands of Sipora, North Pagai, South Pagai, and the nearby islets of Simalegu and Sinakak. Known colloquially as simasepsep.
  • S. c. siberu, found on the island of Siberu. Known colloquially as simakobou.
PIg-tailed snub-nosed langur geographic range. Map: IUCN, 2020

Size, Weight, and Lifespan

Pig-tailed snub-nosed langurs are medium-sized Old World monkeys. Males are nearly 30 percent larger than females, and their canine teeth are 95 percent longer. This example of sexual dimorphism suggests the possible occurrence of male-to-male competition.

Head-to-body length in males ranges from 19.29 to 21.65 in (49-55 cm); average weight is 19.18 lb (8.7 kg). Head-to-body length in females ranges from 18.11 to 21.65 in (46-55 cm); average weight is 15.65 lb (7.1 kg).

The monkey’s so-called “pig tail” adds only another 5.5-5.9 in (14-15 cm) to the body.

Lifespan for the pig-tailed snub-nosed langur is not documented. For a possible clue to its longevity, scientists look at the species’s primate relative, the Endangered proboscis monkey (Nasalis larvatus), who can live up to about 23 years in captivity.

What Does It Mean?

A mating system in which a male and female mate exclusively with each other.

A pattern of mating in which a male animal has more than one female mate.

Visit the Glossary for more definitions


It might be easier to believe that this whimsical-looking primate is a creation of Dr. Seuss—the late, beloved children’s-book author, cartoonist, and animator—rather than a creation of Mother Nature. Surely, one can see a resemblance to the Grinch or maybe to the Cat in the Hat (two iconic creations of Dr. Seuss) in this monkey’s features.

Sitting in the center of a black, hairless face is a small upturned nose, unflatteringly referred to as a snub nose. Elongated nasal bones add a ski slope effect. Had wildlife biologists wished to portray the monkey’s upturned nose as an attractive feature, they could have used the word “retroussé” (used to describe the late, beautiful American film actress Elizabeth Taylor’s snub nose) . . . alas, they didn’t.

In further comparison to the proboscis monkey, the female proboscis is fitted with an upturned nose, similar to the pig-tailed snub-nosed langur’s. However, the male proboscis monkey has a large, exaggerated nose like Jimmy Durante, the late American singer, pianist, comedian, and actor, who referred to his nose as the Schnozzola from the Yiddish slang word “Schnoz” (big nose).

The pig-tailed snub-nosed langur’s lips are narrow and nondescript. Wisps of hair frame the monkey’s face. Chestnut-colored eyes view the world from beneath a slight forehead ridge.

Pig-tailed snub-nosed langurs are asexually dichromatic, meaning that either sex can be one of two color types. Most individuals are cloaked in blackish-brown fur coats; the hair on the nape of the neck, shoulders, and upper back is speckled with lighter-colored hair. About one-quarter to one-third of the population wears a creamy buff-colored fur coat.

Arms and legs of these monkeys are equal length. Their short “porcine” tail is a unique feature among langurs; pig-tailed snub-nosed langurs are the only primates within the subfamily Colobinae to be fitted with a tail that is significantly shorter than their body. Besides being unusually short, the tail is hairless, except for a few strands at the tip.

Photo courtesy of ©Wendy Erb.

Pig-tailed snub-nosed langurs are herbivores (plant-eaters) who eat mostly leaves (making them folivorous), balanced with fruits and berries (making them frugivorous). Young leaves and unripe fruits are favored. They also eat flowers.

Simasepsep monkeys (S. c. concolor) residing on Simalegu island have a penchant for the buds and flowers of the nibung plant, a tall evergreen palm tree.

Behavior and Lifestyle

Pig-tailed snub-nosed langurs are most active during the daytime, making them diurnal, and they spend almost all of their time in trees, making them arboreal. They rarely descend to the ground. A wildlife study (reported in 2008) of those monkeys living in southwestern North Pagai revealed that the monkeys spend nearly equal amounts of their day resting (46 percent) as they spend feeding (44 percent); they spend considerably less time moving (only 7 percent).

Earlier research on the species posited that adult males lead foraging expeditions; however, later research posits that either sex can lead these expeditions, which begin just after sunrise and occur again in the late afternoon. The monkeys may separate while foraging and spread out over an area of up to 98 yd (90 m) in diameter. Their overall territory is between 16 and 50 acres (6.5-20 ha). Members of a group do not stray deep inside other group’s territories; however, they are known to straddle the boundaries of adjacent territories of other groups.

When two males of opposing groups encounter one another, a kind of “face-off” occurs. Each male rapidly moves forward, stopping at about 82 ft (25 m) from the other. At this point, one initiates a “loud call” and the other male reciprocates with his own loud call. Then both males turn and flee back to their home range, leading their respective group members to safety. Earlier research reported that chasing and fighting are uncommon during these male face-offs; later research, however, documents aggressive displays, chases, and fights between the males.

The monkeys move through the rainforest quadrupedally (on all fours). Their long arms have adapted to climbing, and they ascend to the leafy canopy to quietly feed, exhibiting a preference for using their right hand.

Mothers often leave their babies in the crown of a tree while they go off to forage. Known as “parking,” this behavior allows mothers to expend less energy while foraging than if they carried their infants with them.

The dense canopy foliage provides camouflage from predators; if a predator is detected, the monkeys remain completely still and silent to avoid notice. If given no choice, they will descend to the forest floor and flee.

Towering hillside trees that thrust through the forest canopy, 200 ft (61 m) above the forest floor, with trunks measuring 16 ft (4.87 m) in circumference and having densely foliated branches provide the monkeys’ sleeping sites within the forest’s emergent layer. The monkeys might also pass the night in densely foliated trees within the secondary layer of the forest canopy.

Fun Facts

Theodor Seuss “Ted” Geisel (March 2, 1904–September 24, 1991) was an American author, political cartoonist, poet, animator, book publisher, and artist, best known for authoring more than 60 children’s books under the pen name Dr. Seuss).

Dr. Seuss gained inspiration for some of his iconic characters through a visit to Africa. For example, it has been suggested that Dr. Seuss’s famous character the Lorax—a mustached and mossy fellow who “speaks for the trees”—was likely inspired by the long-limbed patas monkeys the children’s book writer saw while on a safari in Kenya. 

Might Dr. Seuss also have been inspired by a curious-looking Indonesian monkey by the name of pig-tailed snub-nosed langur?

Daily Life and Group Dynamics 

Most pig-tailed snub-nosed langurs live in family groups comprised of 3 to 8 individuals, including one adult male, one to four females, and their offspring. The makeup of this family unit can be a single adult couple and their young, or it can include the offspring of more than one adult female sired by one male. Both males and females leave their birth groups; however, males are inclined to leave at an earlier age. Juvenile and adult females temporarily visit and transfer to other groups.

Average group size on the Pagai islands is 4 individuals; in northern Siberut, groups comprise 8 individuals on average.

Less common in this species are small all-male groups. Members of these “bachelor” groups exhibit “bachelor party-ish” behaviors: they make a lot of racket as they travel through the forest and in their “conversations” with one another, and they try to outdo one another with impressive leaps that demonstrate their strength. They also might be trying to catch the eye of nearby females with their macho maneuvers.

Males might also live solitarily, occupying a territory.


Adult males emit a loud call (a series of vocalizations ranging from 2 to 25 nasal barks) to maintain group structure, warn of predators, and announce boundaries. Males also use the loud call when they are startled by disturbances in their environment, such as when a tree falls or when a crash of thunder reverberates through the forest.

Peak time for the loud call is morning and late afternoon; however, these choruses can be heard throughout the day. The average length of a loud call is just over 12 seconds, and the sound can travel more than 1/3 mi (500 m) through the rainforest. A loud call’s first nasal barks are the loudest and are followed by audible gasps. Subsequent calls decrease in volume, with the final barks being faint. Females may respond to a male’s loud nasal barks by answering with sharp squeals.

Tactile communication is also a part of the monkeys’ daily life. Like many nonhuman primates, pig-tailed snub-nosed langurs engage in allogrooming (social grooming between members of the same species). Allogrooming strengthens bonds between individuals, reinforces social structures, establishes family links, and builds companionships.

Reproduction and Family

Human predation influences the mating behavior of pig-tailed snub-nosed langurs. In populations where humans have decimated the population, monogamy appears to be the norm. In areas with denser populations, however, polygyny is the norm.

During estrus, the period when the female is capable of becoming pregnant, her genital area swells and turns pink in color. (Although this trait is not exclusive to pig-tailed snub-nosed langurs, it is rare in other Asian colobines.) Males take notice of the female’s condition, perhaps further enticed by a scent she gives off, and copulation commences. Little information is available about mating rituals or about the reproductive cycle. But it is known that females give birth to a single infant during June or July.

Even less is known about parenting in the species. So, scientists again look to the pig-tailed snub-nosed langur “cousin,” the proboscis monkey, for clues. Female proboscis monkeys carry and nurse their young, and keep them nearby for about a year. Males don’t offer much assistance; however, they do protect their young from males of other groups.

Videos published by wildlife researcher/anthropologist Wendy Erb, PhD. Used with permission.

​Ecological Role

Thanks to their partially frugivorous diet, pig-tailed snub-nosed langurs distribute the seeds of the fruits they eat, via their feces, to help replenish their rainforest habitat.

Conservation Status and Threats

The International Union for the Conservation of Nature has classified the pig-tailed snub-nosed langur as Critically Endangered (IUCN, 2015)—only one step away from becoming extinct. In 2016-2018, the pig-tailed snub-nosed langur found itself on the IUCN’s list of the earth’s 25 most endangered primate species, and then again in the 2018-2020 report. S. c. siberu, the Siberut subspecies, has the largest population size, with an estimated 6,000-15,500 individuals within Siberut National Park. S. c. concolor, the southern subspecies, is urgently in need of protective measures, with a total population of 700-1,800 individuals. The IUCN puts the total population at 6,700 to 17,300 individuals, an alarming decline from an estimated population of 26,000 in 1980. This population continues to plummet; a 90-percent decline over 10 years has been predicted for the species, unless serious conservation actions are taken.

Hunting has taken a devastating toll on all pig-tailed snub-nosed langurs. The creation of roads to access logging operations has provided hunters with easy access to their prey. Hunters now use high-caliber rifles to kill the monkeys. Pig-tailed snub-nosed langur meat is regarded as a delicacy, and entire groups can be eliminated in a single hunt. On the islands of North Pagai and South Pagai, the main range of pig-tailed snub-nosed langurs, twice as many individuals are killed by hunters each year as are born.

Extensive habitat loss throughout the monkeys’ range also threatens their future. In addition to commercial logging operations, forestland has been razed for agricultural use and also converted to palm oil plantations, a death knell for so many species. Human settlements have also encroached upon the monkeys’ habitat.

Conservation Efforts

The pig-tailed snub-nosed langur is listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival; the species is also, in theory, protected by Indonesian law.

However, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce. As an example, even in protected areas such as Siberut National Park, illegal hunting continues.

To help save these monkeys from extinction, the following conservation actions have been proposed.

  • Increased protection for Siberut National Park, which currently lacks enforcement
  • Formal protection of the Peleonan forest in North Siberut, which is home to unusually high primate populations and is easily accessible to hunters
  • Protection of areas in the Pagai islands by cooperating with a logging corporation that has practiced sustainable logging technique there since 1971
  • Conservation education, especially regarding hunting
  • Development of alternative economic models for the local people to reduce the likelihood of selling their lands to logging companies.
our thanks

Many thanks to biological anthropologist Dr. Wendy Erb for allowing us to use her photos of the pig-tailed snub-nosed langur, and for the generosity of sharing her knowledge of the species and field research with us for this profile. 

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Written by Kathleen Downey, September 2018