---
title: "Proboscis Monkey Facts, Habitat, Diet and Big Nose"
description: "Learn why male proboscis monkeys have large noses, where they live in Borneo, what they eat and why the species is endangered."
canonical: "https://uglyanimals.net/animals/proboscis-monkey/"
locale: "en"
content_type: "animal_profile"
primary_entity: "Proboscis monkey"
scientific_name: "Nasalis larvatus"
---

# Proboscis monkey: facts, habitat and what its large nose does

The proboscis monkey is an endangered primate found only on Borneo. Adult males have a long, pendulous nose associated with visual signalling and the resonance of their calls.

## Quick facts

- **Scientific name:** Nasalis larvatus
- **Animal type:** Old World monkey
- **Native range:** Borneo
- **Habitat:** Mangroves, riverine forest, swamp and lowland rainforest
- **Diet:** Leaves, unripe fruit, seeds and some invertebrates
- **Distinctive feature:** Enlarged nose in adult males
- **IUCN status:** Endangered

## What is a proboscis monkey?

The proboscis monkey is a large, reddish-brown leaf monkey in the family Cercopithecidae. It is endemic to Borneo and is strongly associated with forests near rivers, estuaries, mangroves and swamps.

Males are substantially larger than females and have the most pronounced noses. Infants are born with blue facial skin that changes colour as they develop.

## Why does the proboscis monkey have such a big nose?

The enlarged nose is most developed in adult males, which points to a role in sexual and social signalling rather than a general breathing requirement. A larger nose makes the male's face more conspicuous and affects the acoustic properties of calls.

Research and field observations link male calls with group coordination, warnings and interactions with rivals. The nose should not be described as a simple loudspeaker with one proven purpose; it is part of a broader display involving body size, sound and social position.

## Where do proboscis monkeys live, and can they swim?

Proboscis monkeys live in coastal and riverside habitats across Borneo. Groups often sleep near water and move through the canopy during the day.

They are capable swimmers and can cross rivers when necessary. Partly webbed digits and strong swimming behaviour are unusual among primates, but water also exposes them to crocodiles and makes intact riverside forest essential.

## What do proboscis monkeys eat?

Their diet is dominated by leaves, seeds and unripe fruit, with seasonal changes and occasional invertebrates. A specialised multi-chambered stomach supports fermentation of fibrous plant material.

The rounded belly is therefore connected to digestion rather than obesity. Captive or wild diets rich in ripe sugary fruit can be unsuitable for a digestive system adapted to leaves and less sugary foods.

## Conservation status: Endangered

Loss and fragmentation of mangroves, swamp forest and riverine habitat are major threats. Hunting also occurs in parts of the range. Because the species depends closely on lowland waterways, conversion of those habitats can isolate groups quickly.

## Related animals

- [Saiga antelope](https://uglyanimals.net/animals/saiga-antelope/)
- [Aye-aye](https://uglyanimals.net/animals/aye-aye/)
- [Naked mole-rat](https://uglyanimals.net/animals/naked-mole-rat/)

[See more mammals](https://uglyanimals.net/animals/mammals/)

## Related habitats and adaptations

- **Habitat:** [Freshwater and wetlands](https://uglyanimals.net/habitats/freshwater-wetlands/)
- **Habitat:** [Forests and river margins](https://uglyanimals.net/habitats/forests-river-margins/)
- **Adaptation:** [Noses and faces](https://uglyanimals.net/adaptations/noses-faces/)
- **Adaptation:** [Senses and signals](https://uglyanimals.net/adaptations/senses-signals/)

## Sources

- [Animal Diversity Web: Nasalis larvatus](https://animaldiversity.org/accounts/Nasalis_larvatus/): Taxonomy, distribution, habitat, anatomy, diet and social behaviour.
- [IUCN Red List: Proboscis monkey species search](https://www.iucnredlist.org/search?query=Nasalis%20larvatus&searchType=species): Current global conservation category reference.