Proboscis Monkey

Proboscis Monkey

Long-nosed monkey, Bekantan, Monyet belanda monkey

Nasalis larvatus
Population size
Life Span
13-23 years
Top speed
km/h mph 
kg lbs 
cm inch 

The Proboscis monkey (Nasalis larvatus) is one of the largest monkey species native to Asia. It has a characteristic long nose that distinguishes this animal from other monkeys. As a matter of fact, another name of this primate is 'Monyet belanda' monkey, literally meaning 'long-nosed' monkey. When first seeing this animal, people didn't suppose it was a monkey because of its rather unusual appearance. Thus, males of this species exhibit extremely long noses of up to 18 cm (7 inches), which are likely to attract females whose noses are usually shorter.


The Proboscis monkey has a long coat; the fur on the back is bright orange, reddish brown, yellowish brown, or brick-red. The underfur is light-grey, yellowish, or greyish to light orange. Theories for the extensive length of their nose suggest it may be sexual selection by the females, who prefer louder vocalizations, with the size of the nose increasing the volume of the call. The nose is smaller in the female and is upturned in the young. Nevertheless, the nose of the female is still fairly large for a primate. Infants are born with a blue-coloured face that at 2.5 months darkens to grey. By 8.5 months of age, the face has become cream-coloured like the adults. Both sexes have bulging stomachs that give the monkeys what resembles a pot belly. Many of the monkeys' toes are webbed.




Biogeographical realms

These animals are native and endemic exclusively to the island of Borneo in southeastern Asia, where they generally live in coastal areas, covered with mangroves and swamp forests. Other suitable habitats include lowlands along rivers as well as riparian forests and rainforests. Proboscis monkeys typically live in close proximity to water bodies of their home range.

Proboscis Monkey habitat map

Climate zones

Proboscis Monkey habitat map
Proboscis Monkey
Attribution-ShareAlike License

Habits and Lifestyle

Proboscis monkeys are highly social animals, forming troops of 2-30 animals, typically consisting of a single dominant male and multiple (up to 10) females with their offspring. Males defend their group by exposing their teeth and emitting loud, honking signals, while females are responsible for foraging and caring for infants. In areas with sufficient food or close to the water, these troops may occasionally unite in larger aggregations. During these times, groups of Proboscis monkeys rest and sleep among mangroves at the edge of the water. The presence of freshwater bodies such as swamps or rivers is the primary life condition for these animals. Proboscis monkeys are accomplished swimmers. Moreover, when foraging or fleeing from a threat, they are able to take deep dives. Proboscis monkeys communicate with each other using various vocalizations. When claiming the status of the group, males will emit honks; they will also produce alarm calls to signal danger. Both sexes give threat calls, but each is different. In addition, females and immature individuals will emit so-called "female calls" when angry. These monkeys will also make honks, roars, and snarls. Nonvocal displays include leaping-branch shaking and bare-teeth open-mouth threats.

Seasonal behavior

Diet and Nutrition

Being herbivorous (folivorous and frugivorous) creatures, these primates generally feed upon fruits, seeds, young leaves, and shoots of mangroves, supplementing this diet with occasional caterpillars, larvae, and other invertebrates.

Mating Habits

166 days
1 infant
1 year

Proboscis monkeys have a polygynous mating system, where the dominant male mates with females in a troop. They breed between February and November. The gestation period lasts for 166 days, yielding one infant, typically during the nighttime hours. The newborn baby exhibits a deep blue face and sparse, almost black coat, which changes its color within 3-4 months after birth. Collective rearing is common in this species: females of a troop help raise each other's offspring. They can also suckle another female's young when needed. During the first year of its life, the infant is constantly with its mother. However, soon the female produces another baby, after which young females usually continue living with their natal group, whereas males disperse, joining all-male bachelor groups. The age of reproductive maturity is 4 years old in females and 4-5 years old in males.


Population threats

Currently, the biggest threat to this species is the loss of their natural habitat as a result of forest fires and the cutting of mangrove trees, growing along riverbanks. Meanwhile, those in coastal areas lose their range due to the development of human settlements and shrimp farms. Another serious concern is localized hunting for food and intestinal bezoar stones, used in traditional medicine. This threat is compounded by the docile nature of these animals, making them 'easy prey' for hunters.

Population number

The IUCN Red List and other sources don’t provide the number of the Proboscis monkey's total population size. However, according to the IUCN Red List, specific populations have been estimated in the following areas: Indonesia - population number in this country is associated with past and current threats, varying from less than 100 to more than 1,000 individuals; and Sarawak - population in this region is estimated to be less than 1,000 Proboscis monkeys. Overall, Proboscis monkeys’ numbers are decreasing today, and the animals are classified as Endangered (EN) on the IUCN Red List.

Fun Facts for Kids

  • The Proboscis monkey is known as monyet belanda in Malaysia or bekantan in Indonesia.
  • The bulging stomachs of these animals look like pot bellies and they possess some webbed toes.
  • Proboscis monkeys grow this pot belly due to their diet of low-quality leaves. In order to get enough energy, they have to eat large amounts of these leaves, which enlarge their stomachs.
  • Proboscis monkeys consume only unripe fruits since ripe fruits contain sugar that will ferment in their stomachs, leading to fatal bloating.
  • A group of Proboscis monkeys is referred to as a ‘band’ or ‘harem’.
  • When swimming, these primates use a wide variety of techniques such as hitting the water from their bellies.
  • Proboscis monkeys can pass distances of up to 20 meters (65.6 feet) when swimming underwater.
  • The massive noses of male individuals help them produce loud bellowing sounds, which serve as alarm signals as well as help to attract females.


1. Proboscis Monkey Wikipedia article -
2. Proboscis Monkey on The IUCN Red List site -

More Fascinating Animals to Learn About