A group of scientists discovered a new species of worms living in the poisonous Sulphur Cave in Colorado, USA. The team named the worms limnodrilus sulphurensis, blood-red worms that thrive inside a cave filled with toxic gases that can easily kill a person.

The findings, now available in the journal Zootaxa, state that the species is as thin as pencil lead, growing up to 2.5 centimeters long. The blood-red worms are actually partially transparent but they get the intense color from their blood and live clumped together on the cave floor, feeding on the bacteria that grow in damp areas.

Finding the worms was not an easy task. The researchers had to squeeze themselves in the narrow entrance of the 54-meter deep cave.

“It’s sort of foreboding,” David Steinmann, a cave biologist at the Denver Museum of Nature and Science, told National Geographic. “You have to climb and crawl down a wet muddy slop that’s stinky and smells like rotten eggs.”

Although the Sulphur Cave contains toxic gases and stunk of sulphur, it was a magnificent sight to behold. Crystals made of gypsum glitter grow on walls and the cave floor has a small stream where microbial colonies live. Apparently, caves like this one are rare. Some can be found in Italy and Mexico. The high levels of sulphur are believed to originate from the organic matter that got trapped in the cave’s travertine, white or light-colored limestone formed by deposits from hot springs and caves.

The cave’s smell, which resembles that of a rotten egg, is due to microbes converting sulphur into hydrogen sulphide gas. Although the cave’s hydrogen sulfide and carbon dioxide levels are up to four times the levels capable of killing a person, other species besides the bacteria and the worms live in it which include flies, beetles, spiders and other insects.