Creepy-Crawly Cave

Deep inside a cave in Romania, there are creatures that have never seen the light of day. White, eyeless spiders, scorpions, worms, and centipedes scuttle and slither in the darkness. They feed on a thick, floating mat of bacteria that covers an underground lake. The cave and the species that call it home have been sealed off from the outside world for 5.5 million years. During that time, the cave has developed into an ecosystem—a community of organisms interacting with their physical environment—unlike anything else on planet Earth.

Deep inside a cave in Romania live strange creatures. They’ve never seen the light of day. White, eyeless spiders, scorpions, worms, and centipedes scuttle and slither in the darkness. They feed on a thick, floating mat of bacteria that covers an underground lake. The cave and its animals have been sealed off from the outside world for 5.5 million years. During that time, the cave has developed into an ecosystem—a community of organisms that interact with their physical environment. But this ecosystem is unlike anything else on planet Earth.

In 1986, workers preparing to construct a power plant in the city of Mangalia uncovered the Movile (moh-VEE-luh) Cave. Since its discovery, fewer than 100 people have been allowed inside. Not only is the descent into the cave treacherous, but the air inside is hot, humid, and toxic. The area around the cave is known for its geothermal springs. These naturally hot bodies of water release harmful gases like hydrogen sulfide that fill the cave.

A few brave scientists have ventured into the cave’s depths to study its bizarre life-forms. “To many, Movile Cave is the stuff of horror movies,” says Rich Boden, a microbiologist at Plymouth University in England. But he’s intrigued by it. Boden and other researchers hope to learn how the cave’s organisms have adapted to survive—and thrive—in the dark and deadly environment.

In 1986, workers were getting ready to build a power plant in the city of Mangalia. They uncovered the Movile (moh-VEE-luh) Cave. Since its discovery, fewer than 100 people have been allowed inside. Not only is the descent into the cave dangerous, but the air inside is hot, humid, and toxic. The area around the cave is known for its geothermal springs. These naturally hot bodies of water release harmful gases like hydrogen sulfide that fill the cave.

A few brave scientists have ventured into the cave’s depths to study its strange life-forms. Rich Boden is a microbiologist at Plymouth University in England. He says, “To many, Movile Cave is the stuff of horror movies.” But he’s fascinated by it. The cave’s organisms have adapted to survive—and thrive—in the dark and deadly environment. Boden and other researchers hope to learn how they did it.

Scientists think Movile formed under a hill millions of years ago (see How Movile Cave Formed). Back then, the cave likely had an opening in the side of the hill. Water and gas from a geothermal spring inside the cave slowly ate away at the cave’s limestone walls, weakening them until the hill collapsed. The cave and everything inside it—including the organisms living there—were sealed off from the outside world.

Some animals trapped inside the cave couldn’t survive. Movile Cave contains fossils of mice that became extinct long ago. But some creatures developed physical traits that enabled them to live on. “Over time, highly adapted organisms emerged,” says Boden. Above ground, many bacteria use sunlight to turn carbon dioxide gas and water into food—a process called photosynthesis. The microorganisms inside Movile Cave instead rely on chemosynthesis to convert chemicals like sulfur into energy. Tiny crustaceans and worms feed on the bacteria. They, in turn, become prey for predators like scorpions, spiders, and centipedes.

Scientists think Movile formed under a hill millions of years ago (see How Movile Cave Formed). Back then, the cave probably had an opening in the side of the hill. Water and gas flowed from a geothermal spring inside the cave. They slowly ate away at the cave’s limestone walls. This weakened the walls until the hill collapsed. The cave and everything inside it—including the organisms living there—were sealed off from the outside world.

Some animals trapped inside the cave couldn’t survive. Movile Cave holds fossils of mice that became extinct long ago. But some creatures developed physical traits that allowed them to live on. “Over time, highly adapted organisms emerged,” says Boden. Above ground, many bacteria use sunlight to turn carbon dioxide gas and water into food. This process is called photosynthesis. The microorganisms inside Movile Cave rely on chemosynthesis instead. They turn chemicals like sulfur into energy. Tiny crustaceans and worms eat the bacteria. Then they become prey for predators like scorpions, spiders, and centipedes.

Many insects and spiders living inside the cave survive without eyes. They don’t need them since they wouldn’t be able to see in the darkness anyway. Instead, they use their antennae to sense predators or prey. These appendages are often longer than those of similar animals that live outside the cave. Many of the cave’s creatures are also totally white. The pigment, or natural coloring, that normally helps protect animals from sunlight isn’t needed in the cave’s pitch-black environment. 

On the walls of the cave, white spiders spin webs to catch tiny insects called springtails. The largest predator in the cave is a type of brown centipede commonly found in gardens, called Cryptops anomalans. The ones found in the cave, though, are colorless and about three times larger than those above ground. The centipedes have huge antennae and legs but no eyes. The water scorpion Nepa anophthalma also lives in the cave. It’s also missing eyes and pigmentation—unlike its relatives at Earth’s surface.  

Many insects and spiders living inside the cave survive without eyes. They don’t need them. They wouldn’t be able to see in the darkness anyway. Instead, they use their antennae to sense predators or prey. Animals like these that live outside the cave have antennae too. But the antennae of the cave animals are often longer. Many of the cave’s creatures are also totally white. Pigment, or natural coloring, normally helps protect animals from sunlight. But pigment isn’t needed inside the pitch-black cave.

White spiders spin webs on the walls of the cave. They’re trying to catch tiny insects calls springtails. The largest predator in the cave is a type of brown centipede. It’s called Cryptops anomalans, and it’s commonly found in gardens. But the ones found in the cave are colorless, and they’re about three times larger than those above ground. The centipedes have huge antennae and legs but no eyes. The water scorpion Nepa anophthalma also lives in the cave. It’s also missing eyes and pigmentation—unlike its relatives at Earth’s surface. 

When Boden was first asked whether he wanted to go inside Movile Cave to collect samples, he said no. The trip seemed too dangerous. Then he thought, “I’m never going to get another chance. I have to do this!” Six years ago, Boden became the 29th person to venture inside the cave.

Boden descended into the lowest section of the cave, known as the Lake Room. The room contains a pool of water—the same spring that bubbled millions of years ago. Even though the space is only about the size of a small car, it’s teeming with life. There, Boden collected samples of organisms, rocks, and clay. He even bottled up some of the cave’s gas to study back at his lab.

Boden descended into the lowest section of the cave, known as the Lake Room. The room contains a pool of water. It’s the same spring that bubbled millions of years ago. The space is only about the size of a small car, but it’s full of life. Boden collected samples of organisms, rocks, and clay there. He even bottled up some of the cave’s gas to study back at his lab.

Not only does the atmosphere inside the cave contain toxic gases, the air also has just 10 percent oxygen—compared with 21 percent found at Earth’s surface—and more than 80 times the carbon dioxide. After a half hour under these conditions, people start to feel tired and sweaty. Their skin turns red from a potentially deadly condition called hypercapnia, which occurs when there’s too much carbon dioxide in the blood. “You start to feel sluggish,” says Boden. “If someone asked me to pass a container, I had to think about it for a few seconds.” Boden could work safely in this environment for only about four hours before he had to return to the surface.

The samples Boden and other scientists collected are allowing them to learn about the cave’s unique food web and environment. They might help answer larger questions too. “The cave helps us understand life and how it came about,” says Boden. It could even shed light on whether life could exist in other extreme environments, like on Mars.

Not only does the air inside the cave contain toxic gases, but it also has just 10 percent oxygen. Compare that with 21 percent found at Earth’s surface. The cave’s air also has more than 80 times the carbon dioxide. After a half hour under these conditions, people start to feel tired and sweaty. Their skin turns red from a condition called hypercapnia. This happens when too much carbon dioxide is in the blood—and it could be deadly. “You start to feel sluggish,” says Boden. “If someone asked me to pass a container, I had to think about it for a few seconds.” Boden could work safely in the cave for only about four hours. Then he had to return to the surface. 

Boden and other scientists are using the samples they’ve collected to learn about the cave’s unique food web and environment. The samples might help answer larger questions too. “The cave helps us understand life and how it came about,” says Boden. It could even shed light on whether life could exist in other extreme environments, like on Mars.