Cave crawlers.

Dobrogea, Romania - A team of construction workers drilling 18m (60ft) below Earth's surface suddenly came to a halt when they noticed a large opening in the rock. Christian Lascu, a geologist on the site, went down to investigate. He tore away at the earth, making a tunnel large enough to crawl through. When he did, Lascu couldn't believe his eyes. The construction crew had accidentally bored a hole into a mysterious cave.

Apparently the cave, now called Movile, had no natural opening to Earth's surface. So no one knew it was there - or what lived inside. Now, 10 years later, scientists are finding out.

A team of Romanian and American scientists have already uncovered a huge array of unusual troglobites, or cave animals. So far, they've found 48 species. According to biologist Thomas Kane of the University of Cincinnati, who is part of the Movile team, "33 of these creatures have never been seen by humans."

WILD WORLD

It's common to find "weird" creatures living inside caves, says Kane. That's because most caves form underground, when rainwater seeps into and erodes passageways through limestone rock. So cave creatures have to be adapted to living in total darkness with limited food sources. But Movile Cave has an eerier history - and a more bizarre array of life.

"Movile formed when heated water far beneath Earth's surface seeped up into the limestone rock above," says Kane. The water contained hydrogen sulfide gas. When this gas and water combine, they form sulfuric acid.

The acidic water slowly carved out wider passageways in the rock. But until the recent explorers created an above-ground entrance, Kane says, "this cave had been completely sealed for more than 5.5 million years."

That's why the Romanian troglobites are so unusual, Kane explains. "The 33 new species we found in Movile Cave don't exist anywhere else in the world." The cave scientists believe that some of these critters' ancestors lived in a tropical environment millions of years ago. As the regional climate changed, Kane theorizes, the only animals from this group that survived were the ones that had adapted to living in warm underground caves.

"Like most troglobites, all the Romanian cave animals are blind," he says. In total darkness, troglobites don't need to see. Some creatures, like the Movile Cave spider, have no eyes at all.

To make up for their lack of sight, "most cave critters have a sharp sense of smell, taste, and touch," Kane explains. "They use their overgrown antennae or legs to 'see' by feeling their way around."

Because cave-dwelling predators can't see their prey, cave critters do not need coloring for camouflage - or to protect their bodies from the Sun's burning rays. That's why many troglobites, like the Movile crustaceans, are pale or white. "Some of these animals are so translucent (see-through) that you can see their blood flowing," says Kane.

DINNER TIME

Though similar to other troglobites in many ways, the Romanian critters do have an unusual diet. "Most troglobites in other caves eat twigs, leaves, and other plant debris washed in by rainwater," says Kane. But since Movile Cave has no natural ground entrance, such plant material can't get in.

Many of the Romanian critters feast, instead, on the grayish-white mats that cover the cave's walls. Kane says the mats look like wet Kleenex. "When we looked at them under a microscope, we discovered that they are made up of fungi," he says. "Then we found a peculiar type of bacteria growing in the fungi." According to Kane, these bacteria use water, carbon dioxide, and hydrogen sulfide (in the cave's water) to produce food for other cave creatures (just like plants use carbon dioxide, water, and the Sun's energy to produce food for humans). "As far as we know, this doesn't happen in any other cave in the world," Kane says.

But Kane found that not all the Romanian cave critters eat bacteria. For instance, the new blind leech the scientists discovered slurps down whole worms, which is unusual because most leeches are blood-suckers. And instead of spinning a web, one type of long-legged Movile spider uses its sense of smell and hearing to chase down small prey like millipedes.

Kane and his team of cave experts are still searching for other weird creatures lurking in the dark corners of Movile. Luckily, you don't have to be on the team to see them. To get a close-up view of Movile Cave life, check out the critters on these pages.