Most people think of orangutans when they think of Borneo, but Borneo’s tropical rain forests are some of the most wildly biodiverse places in the world. In this rain forest that’s over 130 million years old (that’s 70 million years older than the Amazon), there’s a newly discovered frog with no lungs, a “ninja” slug that fires love darts at its mate, the world’s longest insect, a barking deer and even pygmy elephants—making Borneo a wonderland of wacky and unexpected animals.

These forests are home to around 222 mammals (including 44 endemic), 420 birds (37 endemic), 100 amphibians and 394 fish (19 endemic). Between 1995 and 2010, more than 600 species have been discovered here—that’s three species each and every month—and more than 50 of these species are completely new to science.

Let’s meet some of the fabulously unique creatures you can hope to meet on a Borneo adventure:


Orangutan translates to “man of the forest,” which makes sense given this primate’s uncanny human resemblance. Like us, orangutans have four fingers and a thumb and fingernails. These highly intelligent animals with shaggy reddish fur live in the lowlands and are relatively solitary. They make nests in trees of vegetation to sleep at night and rest during the day, making them the heaviest tree-dwelling animal. They have prominent cheek pads called flanges and a throat sac used to make loud verbalizations.

Orangutan (Pongo pygmaeus) at Tanjung Puting National Park in Borneo, Indonesia

Sadly, orangutan numbers are sharply declining due to habitat being lost at an extremely high rate from the conversion of forests to oil palm plantations and other agricultural development. Fires also destroy massive areas of orangutan habitat. Despite legal protection in Indonesia since 1931, orangutans are still captured and kept in households as status symbols or hunted as food. Females give birth to just one infant every eight or nine years, making their populations very susceptible to even low levels of hunting.

Orangutans feast on wild fruits like lychees, mangosteens and figs and play a vital role in the dispersal of seeds over a huge area. If orangutans were to disappear, so would several tree species.

Proboscis monkey

The proboscis monkey, or nasalislarvatus, is a weird little reddish–brown primate with a long nose (we’re talking up to seven inches in males!). In this species, size really does matter. The longer the nose, the better to attract a potential mate. It also serves to amplify the sound of warning calls. Living on a diet of mainly mangrove shoots and insects to maintain its distinctive pot belly, the proboscis monkey is a strictly protected animal, with experts suggesting that there are only around 1,000 remaining in the wild.

Sun bear

A far cry from the life of a polar bear, sun bears (also known as honey bears) live in the dense lowland forests of Southeast Asia and they resemble a small dogs. A nocturnal and shy species, they are rare to see in the wild. The sun bear is arboreal, so you’ll need to keep your eyes on the trees if you want to see one. You can tell the sun bear from other species from the distinctive horseshoe marks on their chest—no two markings are ever the same! Their tongues are up to 10 inches long and help them to satiate their voracious appetite for honey.

Sun Bear in the rain on a tree branch between leaves at Bornean Sun Bear Conservation Centre Sepilok in Sabah, Borneo, Malaysia

Sun bears are essential members of their ecosystem because they help disperse seeds while also keeping pesky termites in check. Unfortunately, their global population has declined 30% over the last few years, making them the second-rarest bear species next to the Giant Panda. On our Nat Hab Wilds of Borneo tour, we have the chance to enjoy a private visit to the Bornean Sun Bear Conservation Centre. Founded in 2008, the center provides care, rehabilitation and release of orphaned and captive sun bears and increases awareness about the plight of this little-known bear.

Sunda pangolin

The critically endangered Sunda pangolin has been called an “artichoke with legs.” These prehistoric animals have existed for 80 million years. This funky little critter is the only mammal covered in protective keratin scales and has a freaky tongue that stretches out longer than its body. Lacking teeth, this long, sticky tongue serves to collect ants and termites. Though we know they feast on a diet of ants and insects, there’s still not much known about these elusive, nocturnal animals with a prehensile tail. We do know that when threatened, they protect their soft underparts by crunching up into a roly-poly ball.

Sunda Pangolin Borneo

© Frendi Apen Irawan

Sambar deer

The nocturnal sambar deer is one of the biggest species of deer in the world. Adult males can reach a length of more than seven feet and weigh more than 440 pounds (one on record even came in at over a thousand pounds!). They are at home in the Bornean rain forests and are some of the easiest animals in Borneo to spot at dusk and at night. They are timid, but when disturbed, their first instinct is to freeze before responding to predators with loud barks called ‘pooking’ or ‘belling.’ They also dramatically stomp their feet, and their mane will rise in a confrontational manner. They have been listed as a vulnerable species on the IUCN Red List since 2008.

Sambar Deer Borneo

Microhyla nepenthicola

It’s probably easiest to call it by its other name, the “Matang narrow-mouthed frog.” Spotting one of these creatures in the wild is so rare that this is actually a newly discovered species. Just around the size of a pea, this is the second smallest frog in the world, and it loves to live around pitcher plants in Kubah National Park. They were discovered after scientists tracked the unique and powerful croaks of the males. While they are physically tiny, their voice is huge and travels far distances.

Horsfield’s tarsier

These wonderful weirdos with excellent leaping and climbing skills look quite similar to Yoda. They are nocturnal, and their massive yellow eyes help them maneuver through the dark. The size of one of their eyeballs is the same size as their brain, making them the largest-eyed mammal in the world relative to their body size. The forward-facing slope of their eyes allows tarsiers to accurately assess distances for safe leaping—helpful, considering they can leap up to 18 feet. Tarsiers are also capable of turning their heads nearly 180° in each direction, meaning that they can rotate their heads almost 360°.

Horsfield's tarsier

© Bernard Dupont

While they may come across as cute, tarsiers are the only living carnivorous primate species, and they use their dexterous hands to aggressively ensnare their prey. Their medley of insect snacks includes beetles, cockroaches, locusts, moths, grasshoppers, butterflies, ants and cicadas. For a feast, they will go after birds, bats, frogs and snakes—including poisonous species.

Mouse deer

While not technically a deer or a mouse (it’s actually classified as a tragulidae), this nocturnal and solitary critter reaches a not-so-towering height of barely 12 inches, making it the smallest hooved animal in the world. Overachievers, these females can conceive just two hours after birth, and newborn fauns can stand after 30 minutes. They are found on forest floors feeding on leaves, shoots, fruits and sometimes even fungi.

With round bodies and spindly legs, they look almost like a stuffed animal—but inside that cute little mouth are some mighty fangs. A male will angrily beat his hooves when agitated or to ward off predators and warn other mouse deer of danger. Although they are land mammals, they can hold their breath for up to four minutes and often leap into the water to escape predators.

Borneo pygmy elephant

The smallest elephant in the world is among the cutest animals in Borneo with their oversized Dumbo ears and long tails.  Although they only grow to about 9 feet tall, the Bornean pygmy elephant is still the largest mammal on the island. Because of deforestation and hunting, estimates suggest only 1,500 to 3,000 remain in the wild, putting the friendly and adorable elephants in dire need of protection.

Borneo Pygmy Elephant

Once believed to be remnants of a domesticated herd given to the Sultan of Sulu in the 17th century, Bornean elephants were determined by WWF to be genetically different from other Asian elephants. DNA evidence proved that these elephants were isolated about 300,000 years ago from their cousins in mainland Asia and Sumatra.

Clouded leopard

Preferring to live in the treetops, this elusive leopard possesses an incredible ability to climb and hunts smaller mammals, including deer, pigs and even monkeys. Given their nocturnal and stealthy nature, seeing a clouded leopard in the wild is extremely rare.  It’s been called the most beautiful wild cat on earth and is Borneo’s only big cat. Currently listed as vulnerable on the IUCN Red List of Threatened Species, the best chance of spotting the clouded leopard is in Deramakot Forest Reserve.

Clouded leopard Borneo

© Spencer Wright


Hornbills are known for their unusual double-storied bill, but also noteworthy is that they have their own ‘language.’ They seem to speak to each other in a sort of Morse code whose noise resembles that of a steam engine. This form of communication is how a male hornbill sends messages to his mate through the barricade she makes during her nesting period. The pair builds a nest in a tree hollow, and once the eggs are laid, the male seals the female in the hollow, using mud and feces to construct a wall. Only a small hole is left so that the male can pass the food to the female and to the chicks once they are hatched.

Borneo Hornbill

© Brad Josephs

Hornbills are incredibly loyal to their families, mate for life, and will band together to defend each other against predators. Hornbills have an important place in local culture, signifying nothing less than the Spirit of God. It is said that if a hornbill is spotted flying over your home, good luck will be granted to the whole community.

Saltwater crocodile

Crocs are easy to see sunbathing on the banks of Kinabatangan River. Even though these are the saltwater crocs—the most dangerous crocodiles on earth—locals seem to have a peaceful relationship with these animals, which are much smaller than their Australian cousins. Excepting, of course, the legendary man-eater known as “Bujang Senang,” which is thought to have killed 13 people before being caught and killed in 1992.

Sumatran rhinos

Sadly, the Sumatran rhino is on the verge of extinction. It’s unclear exactly how many remain, but estimates suggest fewer than 100 live in northern Sumatra and the heart of Borneo. The Sumatran rhino holds the title of the smallest rhino in the world. Their bodies are covered in long hair, they’re the only two-horned rhinos in Asia, and they have a reputation for being so elusive that even rangers rarely see one. So while it would be wonderful to spot one on a Borneo adventure, realistically, you just have to be happy knowing that they still exist.

Sumatran rhino

Bornean slow loris

The Bornean slow loris, or nycticebusborneanus, is classified as a primate but looks more like a tiny lemur. They are famous for being one of the few venomous mammals in the world. They are tiny and cute with big eyes, and unfortunately, they are in high demand in the pet trade; their sharp, pointed teeth are often clipped with nail cutters without anesthesia before sale. The pet trade is one of the greatest threats to the survival of this species, which is listed as vulnerable on the IUCN red list. The largest populations live in central Borneo and new species of slow loris are still being discovered today.

Slow Loris monkey on tree

Ninja slug

This green and yellow slug (Ibycus rachelae) was recently discovered on leaves at altitudes up to 6,200 feet. The slug boasts a tail that’s three times the length of its head, which it likes to wrap around its 1.6-inch-long body as if it were acting like a cat. In fact, its discoverers originally wanted to name the slug Ibycus felis, after this feline inspiration.

The slug species quickly made a name for itself because of its so-called love darts. Made of calcium carbonate, the love dart is a harpoon-like structure that pierces and injects a hormone into its potential mate, increasing the slug’s chances of reproduction.

Red giant flying squirrel

Red giant flying squirrels are some of the most abundant animals in Borneo, and if you spend any time in the jungle at night, you are pretty much guaranteed to see them. Borneo has a variety of flying squirrels, but the red giant flying squirrel is by far the largest of them all. But know that they don’t actually fly—they simply glide over large distances with the help of a flying membrane flap of skin that extends from their front feet to the back feet.

Red giant flying squirrel

© Brad Josephs

Chan’s megastick

This enormous stick insect, Phobaeticus chani, is believed to inhabit the high rain forest canopy, making it especially elusive and difficult to study. Even though it’s an insect that’s almost two feet long, very little is known about its biology and ecology. In addition to being the world’s longest insect, the species also wins the insect world record for the longest body, measuring an impressive 14 inches.

Only three specimens of this extraordinary creature have ever been found, all of them from the Heart of Borneo. Borneo has long been known as an exciting place for discovering monster insects—the giant cockroaches that were discovered in 2004 being a notable example.

Bornean flat-headed frog

Although first discovered in 1978, in 2008, scientists discovered that this small, less-than-three-inch-long species is the world’s first lungless frog. Instead of lungs, the Bornean flat-headed frog breathes entirely through its skin. Other organs can be found where lungs would normally be, which makes the overall appearance of the frog flatter. This aerodynamic shape allows the frogs to maneuver more capably in the fast-flowing streams that dot their favorite habitats. It is currently listed as endangered on the IUCN Red List of threatened species.