It’s wet, muddy, slimy, and smells like rotten eggs: Sulfur Cave in Steamboat Springs, Colorado, is full of gases so toxic that a person who enters would pass out after just a few breaths. But that didn’t stop David Steinmann of the Denver Museum of Nature & Science. Donning a special respirator, he first explored the cave in 2007. In this extreme environment, devoid of sunlight, Steinmann found clumps of tiny blood-red worms, each one just an inch long and as thin as a pencil lead. Now genetic analysis has confirmed that the worms are a new species that may not be found anywhere else on Earth. These tiny worms could even offer clues to the kinds of life that might be found on other planets.