# Proboscis Monkey (*Nasalis larvatus*)

> The proboscis monkey (Nasalis larvatus) is a large, reddish leaf-eating monkey found only on the island of Borneo, where it lives in mangroves, peat swamps, and riverine forest. Males are unmistakable for their huge, drooping noses and can weigh up to 24 kg, far more than females. Strong swimmers, they cross rivers and can move at up to 24 km/h. They live around 15 to 20 years and are listed as Endangered.

- **Category:** Mammal
- **Conservation status (IUCN):** Endangered
- **Range:** Endemic to Borneo — mangroves, peat swamp, and riverine forest in Sabah, Sarawak, Kalimantan, and Brunei.
- **Canonical page:** https://globalanimalguide.org/animals/proboscis-monkey/
- **Last reviewed:** 2026-07-16

## Scientific classification

- **Kingdom:** Animalia
- **Phylum:** Chordata
- **Class:** Mammalia
- **Order:** Primates
- **Family:** Cercopithecidae
- **Genus:** Nasalis

## Facts at a glance

| Attribute | Value |
| --- | --- |
| Scientific name | Nasalis larvatus |
| Diet | Herbivore — leaves, unripe fruit, seeds, and flowers |
| Habitat | Borneo mangroves, peat swamp, and riverine forest |
| Lifespan | 15–20 years in the wild |
| Weight | 10–24 kg (22–53 lb); males much larger |
| Top speed | Up to 24 km/h (15 mph); strong swimmer |
| Conservation status | Endangered (IUCN) |

## The remarkable nose

The proboscis monkey takes its name from the enormous, pendulous nose of adult males, which can hang down past the mouth. This oversized nose is thought to amplify the male's honking calls and to signal health and status to females. Females and young have much smaller, upturned noses by comparison. No other primate carries a nose quite like it, making the species instantly recognisable.

## Found only on Borneo

Proboscis monkeys live nowhere else on Earth but the island of Borneo, shared by Malaysia, Indonesia, and Brunei. They keep to lowland habitats close to water, favouring coastal mangroves, peat-swamp forest, and forest along rivers. Rarely straying far from the water's edge, they gather in the trees overhanging rivers and estuaries. This tight link to waterside forest makes them especially sensitive to the loss of these habitats.

## Leaf-eating and the pot belly

Proboscis monkeys are herbivores, feeding mainly on young leaves and unripe fruit, along with seeds and flowers. To digest this tough, leafy diet they have a large, chambered stomach full of bacteria that ferment the plant material, giving them a distinctly pot-bellied appearance. This specialised gut means they generally avoid sweet ripe fruit, which can ferment too quickly and upset their digestion. They feed mostly in the morning and late afternoon, resting during the heat of the day.

## Swimming and moving through the forest

Unusually among monkeys, proboscis monkeys are excellent swimmers, with partially webbed fingers and toes that help them cross rivers. They can move at up to 24 km/h and will leap dramatically from trees into the water to escape predators such as crocodiles or to reach the far bank. In the trees they travel by climbing and leaping through the canopy. This swimming ability lets them exploit the flooded, waterlogged forests that many other primates avoid.

## Social structure

Proboscis monkeys live in harem groups made up of one dominant male, several females, and their young, alongside separate bachelor groups of males. At night, many groups gather in trees along the same stretch of river, coming together in loose communities before dispersing to feed by day. Males are much larger than females, weighing up to around 24 kg, and use their size and honking calls to hold their group together. Young males eventually leave to join bachelor bands before trying to win a harem of their own.

## Why it is endangered

The proboscis monkey is listed as Endangered by the IUCN, and its population continues to fall. Its waterside forests are being cleared rapidly for palm-oil plantations, logging, and shrimp farming, destroying the mangroves and riverine trees it depends on. Because the species is confined to Borneo and tied to a narrow band of habitat, it has little room to retreat. Protecting mangrove and riverside forest is critical to its future.

## Frequently asked questions

### Why do proboscis monkeys have such big noses?

Only adult males have the huge nose, which is thought to amplify their honking calls and signal health and status to females. Females and young have much smaller, upturned noses.

### Where do proboscis monkeys live?

Proboscis monkeys are found only on the island of Borneo, in Malaysia, Indonesia, and Brunei. They live in lowland habitats near water, including mangroves, peat-swamp forest, and forest along rivers.

### Can proboscis monkeys swim?

Yes. They are among the best-swimming of all monkeys, with partially webbed fingers and toes. They will leap from trees into rivers to cross to the other side or to escape predators such as crocodiles.

### What do proboscis monkeys eat?

They are herbivores that feed mainly on young leaves and unripe fruit, along with seeds and flowers. Their large, chambered stomach ferments this leafy diet, giving them a pot-bellied look.

### How big do proboscis monkeys get?

Males are much larger than females and can weigh up to around 24 kg (53 lb). This large size difference between the sexes is typical of the species.

### Why are proboscis monkeys endangered?

They are Endangered mainly because their waterside forests on Borneo are being cleared for palm-oil plantations, logging, and shrimp farming. Confined to a single island and a narrow band of habitat, they have little room to retreat.

## Sources

- [IUCN Red List — Nasalis larvatus.](https://www.iucnredlist.org/search?query=Nasalis%20larvatus&searchType=species)
- [Animal Diversity Web — Nasalis larvatus. University of Michigan Museum of Zoology.](https://animaldiversity.org/accounts/Nasalis_larvatus/)

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Source: Global Animal Guide (https://globalanimalguide.org/animals/proboscis-monkey/). Licensed CC BY-NC 4.0 — free for non-commercial reuse with attribution.