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Deer Cave – The World’s Largest Cave

Welcome to the world’s largest natural rock chamber – accessible by a beautiful planked walk through the buzzing jungle of Mulu, and home to some of the most bizarrely adapted cave species is Deer Cave. Imagine it, its 5pm and the sun is rising in the exciting air of Borneo. The sky dangerously suddenly becomes blackened by the 1 million bats that flock and darken the sky in search of food. This is just one of the many extraordinary treasures behind Deer Cave.

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So you’re walking through a cave large enough for a jumbo jet to fly above your head, around you sits the keystone species holding the caves ecosystem together – over 3 million wrinkle lipped bats. Their mounds of droppings known as guano accumulate on the caves floor, rising up to a whopping 300m. It is this essential nutrient that acts as the food source in Deer cave – one of the few ecosystems that do not rely on plants and sunlight.

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Sifting through the guano with itching legs and antennas are cockroaches, earwigs, scorpions, crabs and giant centipedes. Millions of these are consumed each night, and without these keen catching bats insect populations would spiral out of control and disrupt the delicate balance of Thailand’s forest ecosystem.

Weaved amongst the eyes and ears of bats, sits specially constructed nests of swifts. These nests have been cleverly crafted by the salvia of swifts that dry and form small nests which cling safely to the caves walls. These nests are considered a delicacy in Asia, so local inhabitants often enter the caves on advanced built ladders of vine, and gather the swifts nest made of spit. These are popularly transformed into Bird nest soup – a food that bears the same value as silver.

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Above the tourists that flock to the cave to catch glimpses of the caves dense personality, glow worms eerily hang from mucus hammocks waiting in the darkness to snare up some prey. These are one of the most bizarre findings in Deer cave, but are nevertheless extremely adapted to life without sun and full of insects. The glow worm produces dozens of threads from the silk glands in their mouths, and reel these out just like a keen fisherman with a line. Instead of working with bait, the glow worm works with silk. It sits there waiting, encased in a ghostly blue light luring and attracting prey.

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Glistened across the ceilings in the dark, dripping echoes of the cave, we can challenge that these worms are the stars of Deer Cave.  Once an insect becomes dazzled by the light and draws closer for a look, they become trapped in the sticky lines and from here there is no escape. All catch are consumed alive. This amazing video delivered by BBC is the prefect capture of the strange fisherman tactic of the glow worm.

Settling in the streams of the crystal clear waters is the rare Texas blind salamander – another peculiar species adapted to life in the caves. With no sunlight and no requirements to see this salamander has not only lost its pigment in its skin but has also lost its eyes. To replace such a loss has formed extremely adapted receptors in the skin which detect the tiniest movement in the water.

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So what ever the flow of the river delivers to the salamander, whether it is a blind shrimp or snail the Texas blind salamander rarely ever fails to consume these. Living in waters so low in oxygen is the key behind their blood-red external gills, allowing an easier diffusion of oxygen from the water. These weird beauties are extremely rare with less than 100 present in caves and can be seen in this amazing short video delivered by David Attenborough.

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Another rare species only living in two cave waterfalls also swims the waters of Deer cave – the Blind Cave fish. Despite lacking eyes, these have an uncanny ability to navigate skilfully by bouncing sound waves off objects and the walls around them. With tiny microscopic hooks on their fins, blind cave fish pin to the bottoms of streams and remain to feed on the abundant bacteria in the fast flowing water.

So how did the home to such peculiar species become so large?

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The conditions have to be favourable for large caves to develop and Mulu has the required conditions for Deer Cave to thrive so well. The most important is rainfall – and with Mulu recording an average annual rainfall of 5700mm gives a rapid run off into the limestone fissures. Rivers flowing off the Mulu sandstones are a continuous delivery of solutions. These have very high erosive capacities and combined with the strength of the limestone enables development of very big caves.

The limestone has stunningly formed stalactites and stalagmites – all astonishing masterpieces of nature over thousands of years. Large varieties stack the grounds and droops off the ceilings from the variation of air flow and currents. In some areas both the stalactites and stalagmites have become so large they have joined together forming magnificently impressive columns.

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From a starred sky produced by glow worms, to nests made out of spit, to the thousands of guano droppings we can see that the ecosystem of Deer cave is a very uniquely evolved cave of species, beauties and even delicacies. Gaining its name from the rare species of Deer which lives in Malaysia, I can confidently say that Deer cave is also an extremely rare habitat striving in species diversity and bizarreness, with a complete perfect working environment that lacks plants and sunlight but makes up for in beauties and mysteries.

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  • Daven

    Those are absolutely beautiful.

  • Emma

    Thank you very much Daven :)
    I would absolutely love to see this large beauty one day.

  • claire

    Stunning article

  • sheena


  • Tom S.

    Thailand? Deer cave is on the Malaysian part of Borneo, an island that’s quite far from Thailand.

  • Pingback: Souper Duper! Asia’s Artificial Bird’s Nest Soup Shacks | WebEcoist

  • Raam

    Well researched article. The beautiful snaps further enhanced the article.

  • Fynt

    WHat a beautiful post! I love this site!

  • Bob Roberts


  • Bob Roberts


  • Bob Roberts