Deer Cave & Lang’s Cave

activities / Extreme sports

Lonely Planet review

A lovely 3km walk (40 minutes to 60 minutes) through the rainforest along a plankwalk takes you to these adjacent caverns. The highlight here is not so much what’s in the caves as what comes out of them every evening around dusk (unless it’s raining): millions of bats in spiralling, twirling clouds that look a bit like swarms of cartoon bees. It’s an awe-inspiring sight. The bats’ corkscrew trajectory is designed to foil the dinner plans of bat hawks perched on the surrounding cliffs. Count on getting back to park HQ at around 7pm.

The Mulu Bat-Cam – in fact, five infrared webcams - follows the lives of bats inside the Deer Cave. It’s not internet live-streamed yet but you can see the feed at the Bat Observatory , next to the cave’s grassy bat-viewing amphitheatre, as well as back at HQ in the park office.

The Deer Cave – over 2km in length and 174m high – is the world’s largest cave passage open to the public. (It was considered the world’s largest cave passage, full stop, until what may be an even larger one was discovered in Vietnam in 2009.) It is home to two million to three million bats belonging to 12 species (more than in any other single cave in the world) who cling to the roof in a seething black mass as they gear up for their evening prowl.

We’re not sure who did the calculations or how, but it’s said that the Deer Cave’s bats devour 30 tonnes of mosquitoes every night. That’s one reason why mosquito bites are almost unknown at Mulu.

If it’s raining, the bats usually (but not always) stay home because echolocation (the way they find prey) is not very good at honing in on flying insects amid an onslaught of raindrops.