When David Steinmann first wriggled into Sulphur Cave near Steamboat Springs, Colorado, in 2008 he was surprised to find knots of blood-red worms.

Though finding worms in most caves isn’t unusual, this was no ordinary cavern—it is filled with toxic hydrogen sulfide gas, reports Erika Engelhaupt for National Geographic. Steinmann, Research Associate of the Zoology Department at the Denver Museum of Nature & Science, was among a small team of researchers who are studying the ecosystem of this unusual cave.

And the field excursion was no small task. The researchers used special breathing equipment during the exploration, since the levels of hydrogen sulfide gas inside the cave can reach levels that could kill a person. A rescue team remained stationed outside the entrance as a precaution, writes John Wenzel for The Denver Post.

Researchers studied the worms for over 1,000 hours before certifying them as a new species, Limnodrilus sulphurensis. They documented the find the journal Zootaxa.

The worm's harsh habitat classifies it as an extremophile, an organism capable living in a place where most species would perish, including inside volcanoes and hot ocean vents, under Antarctic ice and at the bottom of the Mariana Trench, the deepest spot in the ocean.

Sulphur Cave is the definition of an extreme environment. It is covered in slime and “snottites,” mats of bacteria that look like mucousy globs hanging from the ceiling that drip sulphuric acid strong enough to burn through clothing, according to Engelhaupt. And the sulfur makes it smell strongly of rotten eggs.

Yet somehow, life persists.

The worms are each about an inch long with transparent body segments roughly the thickness of pencil lead. Because they live in the low-oxygen cave, their hemoglobin binds to oxygen much better than other species, which may give them their red color, Frank Krell writes for the Denver Museum of Natural and Science blog.

Riftia tube worms near deep-sea ocean vents that produce hydrogen sulfide have a similar blood red color Engelhaupt notes. The ocean worms survive by using bacteria-filled structures called trophosomes in which the bacteria process hydrogen sulfide and produce energy the worm can use. But when microbiologist Norman Pace from the University of Colorado, Boulder, examined the Sulphur Cave worms, he didn’t find similar structures.

According to Krell, the hydrogen sulfide levels in the cave are ten times higher than the concentrations found at sea vents. Instead of using trophosomes, the worms eat bacteria on the cave floor. Their special hemoglobin probably helps protect them from the hydrogen sulfide in their environment and there's some evidence the worms can digest the sulfide themselves.

The unique species is could be useful in other disciplines and may even be a model for how life could exist on other planets. The scientists are continuing to study the squiggly masses to see if their blood perhaps contains some form of antibiotics or detoxifying substances, Steinmann tells Wenzel.