Changing Planet

WATCH: Billions of Bugs Feast on Flesh and Dung in Borneo

The Gomantong Caves in Borneo are the type of place that makes most people want to tuck their socks into their pants and run the other way. First imagine the amount of feces that millions of bats and swiftlets produce … and then imagine how many feces-feasting bugs that would attract. And that’s exactly what you have to walk through in order to explore what some have dubbed “the Cockroach Cave.”

Cave ecologist and National Geographic grantee Donald McFarlane says he finds the bird and bat guano “spectacular” because of all the life it sustains. The cockroaches are “innumerable,” he says, and “in some places their numbers are so dense that there is almost no space between one cockroach and the next.”

Cockroaches aren’t the only frights in the cave. Injured or dying birds and bats, as well as a mix of living and dead flies, ticks, and other bugs, rain down from above. Expedition member Keith Christenson says that while working in caves, scientists also need to be on high alert for “wheelbarrow-loads of guano that calve off from above,” as the stench can stick to you for several days—because, he says, “It’s really hard to wash out all the small bits of insect exoskeleton that are in the mix.”

While the scientists try to avoid the droppings that are dropping, hungry insects on the ground make a mad dash for the falling dung—that is if they’re not already feasting on a dead or dying bat.

If a bat is alive when it hits the cave floor, it won't be for long. Bugs can skeletonize a bat with impressive speed.
If a bat is alive when it hits the cave floor, it won’t be for long. Bugs can skeletonize a bat with impressive speed. (Photo courtesy Keith Christenson)

With dung-feasting bugs all around them and creepy-crawly creatures falling from above them, “the invertebrate experience is overwhelming,” McFarlane says.

But for McFarlane, it’s overwhelming in a fascinating way. “In contrast to a tropical forest where a lot of the organisms are hiding and you have to search for them, in these caves the whole ecosystem is laid out in front of you, it’s all around you,” he says.

McFarlane hopes to reveal more about this impressive ecosystem in order to protect it. For about three centuries swiftlet nests have been harvested in Gomantong for the Asian delicacy bird’s nest soup. McFarlane wants to “map the caves in great detail to understand the interaction between the biology and the geology of the caves to contribute to sustainable management of the edible nest industry.”

The biology to which McFarlane is referring is, in part, the massive amounts of guano the bats and birds produce. “Our starting hypothesis is that the metabolic activities of the birds and bats—the breathing and excretion and so on—affect the cave walls,” he says. “The bats and the birds in the cave, because of their very large numbers, erode the cave walls and make the cave larger. We think that we’re looking at perhaps 50 percent or so of the volume of the cave actually being created by the animals rather than the more traditional ways in which caves are formed by underground rivers and so forth.”

McFarlane, Christenson, and the rest of the expedition team produce very detailed cartography and scan the cave with state-of-the-art underground terrestrial lasers to figure out how much the animals are affecting the cave geology and to also determine how edible nest harvesting is affecting the Gomantong swiftlet population.

While it’s people who harvest swiftlet nests, there is another creature that the birds would also prefer to avoid: giant cave crickets. These crickets are known to steal swiftlet eggs or even feed on recently hatched chicks. McFarlane’s team also got a bit of scare from a giant cave cricket—but you’ll have to watch the video to see how that turns out.

To watch more of McFarlane’s work in the Gomantong Caves, be sure to check out Bat Man of Borneo.

Nora Rappaport is a producer and editor on National Geographic's Science and Exploration Media team. She produces content that highlights the awe-inspiring work of National Geographic explorers around the globe. When not working with her colleagues to inspire people to care about the planet, Nora can be found hanging out with any number of dogs.

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