A new species of worms named Limnodrilus sulphurensis have been found inside the Sulphur Cave in Steamboat Springs. Photo courtesy David Steinmann.

Hidden in one of Colorado’s iconic ski towns lies a mysterious caved laced with deadly components.

Called the Sulphur Cave, it's unlike any other cave in the state, according to David Steinmann, Research Associate of the Zoology Department at the Denver Museum of Nature & Science.

The cave is located in Steamboat Springs nestled at the foot of an in-town ski hill. It’s about 25 feet deep and 200 feet long. The ceilings are extremely low with little to no room for standing. Filled with thin tubular crystals, it is as beautiful as it is delicate. Water from the town’s hot springs flows naturally into the cave’s dark and shadowy entrance, forming a small stream along its muddy, soupy floor. As cold air pushes its way through small narrow openings of rock, a strange natural phenomenon awaits.

The cave itself is beautiful, but this natural wonder quickly morphs into a harsh and uninviting environment. Deadly gases and strong, smelly odors deter all those who marvel at what’s inside. Acid so strong it will burn through your clothes drips from the cave’s ceiling. According to Steinmann, lethal levels of toxic gases consisting of hydrogen sulfide and carbon dioxide will cause a person to pass out just after a few breaths, which could be followed by death.

Here’s where things get even odder.

Tens of thousands of “blood-colored” worms have been found thriving inside the cave, grazing on sulfur-oxidizing bacteria. These long slender worms called Limnodrilus sulphurensis live together in dozens of clusters, mostly in the water or along wet surfaces. This new species of worm is only known to exist in Steamboat Springs, according to Steinmann who has been studying the cave for more than 20 years. He uses special equipment and SCBA (Self-Contained Breathing Apparatus) to safely explore the dangerous area.

Steinmann described the worms as bright red with a web of veins on their skin. He also noted that the worms are extremely sensitive to light, retreating and hiding when exposed to it. While the tiny wavering critters are typically found living inside the Sulphur Cave, a few have been spotted in nearby hot springs. Other life-forms found in the cave include spiders, flies, beetles, springtails, and millipedes.

The Sulphur Cave at Howelsen Hill is also pending consideration for a National Natural Landmark through the National Park Service, according to a recent report from the Steamboat Pilot.

According to an archived edition of Steamboat Pilot, an Italian exchange student who first entered the cave with only an oxygen mask came out convulsing and falling in and out of consciousness with “wild eyes.” The incident reportedly occurred in 1962.

According to the Denver Museum of Nature & Science, hemoglobin allows these tiny wavering critters to bind oxygen extremely well, so they are able to survive in harsh and low oxygen environments. Scientists came together from the United States, Germany, and Sweden to collectively describe the new worm species, which can be seen at the Denver Museum of Nature & Science. The new species is part of their permanent collection, along with over one million other Zoology Department specimens.

The cave has been well known for about 100 years. Native American legends believed the cave was a sacred site, offering a gateway to the “underworld.”

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