Sulphur Cave in Colorado Home To Blood-Red Worm Blobs : Short Wave In the toxic waters of Sulphur Cave in Steamboat Springs, Colo. lives blood-red worm blobs that have attracted scientific interest from around the world. We don special breathing gear and go into the cave with David Steinmann, the spelunking scientist who first documented the worms, along with a trio of science students from Georgia Tech, to collect worms and marvel at the unique crystals and cave formations (ever heard of snottites??) that earned Sulphur Cave a designation as a National Natural Landmark in 2021. Then we learn about how extremophiles like these worms are helping scientists search for new antibiotics, medicines, or in the case of the Georgia Tech team, models for worm blob robots that can explore uneven, dangerous terrain, like caves on other planets.

Worm Blobs From The Bowels Of The Earth

Worm Blobs From The Bowels Of The Earth

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Darshan Chudasama, a graduate student in the Bhamla Lab at Georgia Tech, emerges from Sulphur Cave in Steamboat Springs, Colo. with a vial containing toxic spring water and the worms who live in it. City of Steamboat Springs hide caption

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City of Steamboat Springs

Darshan Chudasama, a graduate student in the Bhamla Lab at Georgia Tech, emerges from Sulphur Cave in Steamboat Springs, Colo. with a vial containing toxic spring water and the worms who live in it.

City of Steamboat Springs

The three science students from Georgia Tech arrive in brand-new Dickies coveralls, ready to enter the bowels of the Earth.

"Sulphur Cave is a really dangerous place," says David Steinmann, a veteran caver and research associate with the Denver Museum of Nature and Science, gathering all the explorers at the mouth of the cave. "If you take the precautions we are and have the gear and the gloves, then you will be safe. I hope."

Sulphur Cave doesn't look particularly dangerous from the surface. It's a hole in the ground at the side of a ski run on Howelson Hill in Steamboat Springs, Colorado, surrounded by a wooden fence. A stream bubbles up from a spring nearby, reeking of sulfur, and slopes into the hole, adding a persistent waft of rotten eggs to the air.

But underground, the cave is unique. One of only a handful of sulfur caves in the world, it was designated a National Natural Landmark by the National Parks Service in 2021. One big reason is that it's home to a creature that has drawn the interest of scientists around the globe: a small, blood-red worm that lives in the toxic waters in wriggling wormy blobs.

"The Sulphur Cave worms are most interesting because they can live where nothing else in the world would normally be able to live," says Steinmann, a wetlands biologist who was one of the first to document the worms in 2007.

The worms belong to the category of organisms known as extremophiles–critters capable of living in extreme environments. They're like catnip to scientists, because many have evolved novel compounds and biological processes that researchers can use to develop new antibiotics, medicines, or in the case of the Georgia team, models for robots that could explore dangerous, uneven places.

Thousands of worm blobs, made up of dozens of individual Limnodrilus sulphurensis worms each, live off sulfur-eating bacteria in Sulphur Cave's toxic spring waters. Norman R. Thompson hide caption

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Norman R. Thompson

Thousands of worm blobs, made up of dozens of individual Limnodrilus sulphurensis worms each, live off sulfur-eating bacteria in Sulphur Cave's toxic spring waters.

Norman R. Thompson

First Priority: Breathing

Before they can go in to find the worms, the spelunking scientists have to suit up in self-contained breathing apparatuses, which consist of an oxygen tank and a face mask, because the air in the cave contains lethal levels of hydrogen sulfide and carbon dioxide.

"I've worked in submarines before, so for me this is no big deal," says Harry Tuazon, noting that they used SCBAs when fires broke out in the sub–mostly due to uncleaned dryer lint traps–before attaching the respirator hose to his face mask with a click and loud expulsion of air.

Tuazon is a Navy officer-turned-PhD student at Georgia Tech studying bioengineering at the Bhamla Lab, and he's the first to go into the cave with Steinmann.

With their SBCAs making breathing noises reminiscent of Darth Vader, the two descend carefully down the steep stream bed to a vertical crack at the bottom, and then squeeze into the cave.

"Now we're down in here a little bit, right in the zone where the air's getting really toxic," says Steinmann, his muffled voice coming through the SCBA's speaker.

The ceiling of Sulphur Cave is covered by delicate crystals and snottites--tiny stalactites that look like they're dripping mucous, but are in fact colonies of bacteria dripping sulfuric acid, which they excrete as they digest hydrogen sulfide in the spring water. Norman R. Thompson hide caption

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Norman R. Thompson

The ceiling of Sulphur Cave is covered by delicate crystals and snottites--tiny stalactites that look like they're dripping mucous, but are in fact colonies of bacteria dripping sulfuric acid, which they excrete as they digest hydrogen sulfide in the spring water.

Norman R. Thompson

Inside, the cave is beauty writ small. The main room is roughly 75 feet long and five feet tall. The ceiling is covered in delicate crystal formations that glisten in the light of the headlamps.

"You wouldn't know it, obviously, but looking around at the ceilings and the wall, they're actually covered with thousands of species of different bacteria," Steinmann says.

On most surfaces, the bacteria forms a yellow-white layer that comes off like a paste when touched. But some of the bacteria colonies form dark, winding, rope-like formations called biovermiculations, which Steinmann thinks look like brain coral.

Other colonies form straw-like structures hanging from the ceiling that cavers have dubbed snottites, because they look like stalactites made of mucous. It might be a cute name, but the snottites drip sulfuric acid, which the bacteria have metabolized from the hydrogen sulfide that seeps through the rock. The acid's pH is low enough to burn skin and clothes if left in prolonged contact.

Scientists in 2007 surveying the cave. A sickly-white paste comprised of hydrogen sulfide and hundreds of species of bacteria covers most of the cave's surfaces. Norman R. Thompson hide caption

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Norman R. Thompson

Scientists in 2007 surveying the cave. A sickly-white paste comprised of hydrogen sulfide and hundreds of species of bacteria covers most of the cave's surfaces.

Norman R. Thompson

"Like Something On Another Planet"

On the ground, the stream widens over the cave floor and disappears into darkness. The streambed and rocks are also coated in a yellow-white mat of bacteria, giving the whole cave a ghostly, otherworldly feel.

And that's where Steinmann finds them.

"If you look, you can see clumps of worms everywhere," he says, pointing at the floor. "There are thousands and thousands."

The worm blobs look like dark-red sea anemones wriggling in the stream bed. The individual worms are around one-inch long, thin as pencil lead, and live off the bacteria in the cave, which in turn lives off the sulfur.

"When I first entered the cave, it seemed like a very pristine and undisturbed environment, almost like something on another planet," says Steinmann. "It reminds us of where we might one day find life in caves underground on other planets in our solar system."

Steinman was the first person on this planet to report seeing the worms.

David Steinmann collects worms. "The Sulphur Cave worms are most interesting because they can live where nothing else in the world would normally be able to live," he says. Norman R. Thompson hide caption

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Norman R. Thompson

David Steinmann collects worms. "The Sulphur Cave worms are most interesting because they can live where nothing else in the world would normally be able to live," he says.

Norman R. Thompson

In 2007, he was invited to join a group of scientists to survey and document Sulphur Cave. They blew oxygen into the cave with fans so they could go in without SCBAs, and Steinmann went in first, so he could collect samples of the cave life before the other researchers disturbed it. He has a reputation for discovering new species in caves.

"Over the last 20 years, I've found about a hundred new species," he says. "Maybe a couple dozen have been named so far, and there are many more out there. I sort of like to joke with my friends that if I want to find a new species in a cave, all I have to do is go to a cave I've never been to before, and almost guaranteed, if there's a little moisture, I'll find something."

That's because caves are like little islands of evolution–or what Steinmann calls microhabitats. Because they're cut off from most other habitats, and tend to stay at a steady temperature year round, the critters in them tend to evolve to fit each specific cave.

"Many of the cave creatures have evolved to have no pigments–they're albino," says Steinmann. "They get really long legs and lots of sensory hairs on their body to feel around in the dark, and their eyes become reduced and reduced sometimes to nothing."

Biovermiculations are an underground formation with the consistency of wet clay that is created by a mix of microbes and sediment. Scientists are only beginning to understand how and why they form. Norman R. Thompson hide caption

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Norman R. Thompson

Biovermiculations are an underground formation with the consistency of wet clay that is created by a mix of microbes and sediment. Scientists are only beginning to understand how and why they form.

Norman R. Thompson

Tiny Worms, Extreme Potential

After analyzing the worms, Steinmann and several other researchers were able to announce that they were a new species to science that lived only here and in a nearby stream. They named them Limnodrilus sulphurensis. And word spread in extremophile circles.

"I've just been finding more and more researchers over the years have been contacting me to see if I could collect worms for them, so they could study them in new ways, like antibiotics, the robotic worms, the physiology, the blood, the detoxifying substances," Steinmann says.

Scientists tend to be interested in extremophiles for two reasons: first, because they have evolved to live in environments that are deadly to most life on Earth–whether too cold, too hot, too acidic, too radioactive, too sulfurous–they can serve as models for how life might evolve on other planets where the chemical makeup of the atmospheres and liquids are different from Earth.

Second, the biology they've evolved to live in these environments often relies on unknown compounds and chemical processes that have proved to be useful to scientists studying everything from biofuel to lactose-free milk to ways to clean up toxic spills.

For their part, the sulfur worms offer several tantalizing puzzles.

The Georgia Tech students will take worms back to the lab to study how they move as an entangled group to help them develop models for creating a worm swarm robot that can explore uneven terrain. City of Steamboat Springs hide caption

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City of Steamboat Springs

The Georgia Tech students will take worms back to the lab to study how they move as an entangled group to help them develop models for creating a worm swarm robot that can explore uneven terrain.

City of Steamboat Springs

Steinmann said one researcher told him the sulfide-filled spring water is 10 times more toxic than volcanic vents in the bottom of the ocean, and so scientists are studying how the worms can detoxify the sulfide. Steinmann says they have thus far detected two substances, using gas chromatography: one they're familiar with, and one that's a mystery.

The spring water here also contains oxygen levels so low that few organisms could survive, so the worms have adapted powerful circulatory systems. "They have blood that binds oxygen amazingly well," says Steinmann. He likes to joke that athletes wish they had worm blood, pointing to another potential medical application.

Researchers in France have requested the worms to look for new antibiotic compounds that may help the worms live alongside hundreds of species of bacteria in the cave–compounds that might prove fruitful against the antibiotic-resistant bacteria strains that are becoming a growing problem.

Worm-Bots And More

And then there's Tuazon and his team from Georgia Tech. They're particularly interested in how the worm blobs move around as a cohesive group despite having no leadership.

"I'm looking into the biology, physics, all the way to the robotics," says Tuazon. "For these worms, we're trying to come up with rules to say, how can they locomote together in an entangled group? We're trying to apply them into the field of, let's say, underwater exploration, cave explorations, maybe space. So we'd like to take that aspect, create rules and model after it, and apply it to swarm robotics."

The Bhamla Lab where Tuazon studies has already made one such robot modeled after blackworms.

Robots that can explore other planets? Novel antibiotics? Compounds that could oxygenate our blood? It's a lot to hope for from some wriggling worm blobs that only live in this small cave in Colorado, but for Steinmann, it all adds to the wonder of the worms.

"We first found the worms in 2008," he says. "Here we are in 2022, 14 years later, and we're still discovering new attributes and features of these unusual worms. And I think there's really a lot more to be looked at."

This episode was produced by Thomas Lu, edited by Gabriel Spitzer, and fact-checked by Rachel Carlson. The audio engineer were Gilly Moon and Josh Newell.