The Proboscis Monkey (Nasalis larvatus), also known as the long-nosed monkey, or in Indonesia as "bekantan", "monyet belanda", and even "orang belanda" as Indonesians remarked that the Dutch colonizers often had similarly large bellies and nose, is an arboreal Old World monkey with an unusually large nose, a reddish-brown skin color, and a long tail. It is endemic to the southeast Asian island of Borneo and is found mostly in mangrove forests and on the coastal areas of the island.
This species co-exists with the Bornean orangutan and monkeys such as the silvery lutung. It belongs in the monotypic genus Nasalis.
They are famous for their freakishly large noses and their pot-bellied stomachs. The males have these big noses to resonate territorial calls. They let out a loud growling call, and the large, fleshy noses echo the calls and make them louder. This tells both predators and rival males to keep out. The noses also attract females. The males with the bigger noses usually mate with the most females. When feeding, the males have to use one hand to eat leaves, and the other to hold their nose up because its so big. The males are also very large. They can weigh up to 50 lbs, mainly because of their huge stomachs. They have 4-chambered stomachs to digest the hardy leaves they eat. Each chamber digests the leaves a little more so the next stomach will have it easier, until the leaves are fully digested. As a seasonal folivore and frugivore, the proboscis monkey eats primarily fruit and leaves. It also eats flowers, seeds and insects to a lesser extent. Proboscis monkeys will spend most of their lives near a source of water. As a defense, they will jump into the water to escape predators like Sunda clouded leopards, reticulated pythons and serpent eagles, although it leaves them vulnerable against the false gharial. They are the only monkeys who are so comfortable in and around water. They even have webbed feet and will dive underwater if they need to.