What lies beneath: Inside an Illinois cave

Chris Young

Deep inside the cave, there’s no getting accustomed to the darkness.

It’s just dark. No light. None.

And somehow, life continues to find a way to survive — even thrive — there.

At Illinois Caverns State Natural Area near Waterloo, not far from St. Louis, dozens of organisms call the cave home.

But adapting to what would seem to be an inhospitable environment for competitors isn’t always a safe bet anymore.

That’s because the delicate, low-energy cave environment easily can be upset by human behavior on the surface.

Illinois Caverns is in one of Illinois’ karst regions, where water drains from the surface into sinkholes and into underground streams.

Water finds cracks in the limestone bedrock, and when it mixes with the carbon dioxide from the atmosphere it creates a weak carbonic acid that dissolves a larger and larger path over time.

Water cuts and builds at the same time. Dissolved minerals are deposited and form many of the spectacular cave features.

Land around Waterloo is considered part of Illinois’ sinkhole plain. Cave residents rely on debris from the surface washing into the cave and bringing the sun’s energy along.

A trip through Illinois Caverns likely will turn up occasional piles of leaves or other organic debris from the surface that has washed in through a sinkhole.

“That is normal and healthy for a cave — in moderation it is,” says Steve Taylor, a biologist studying cave invertebrates at the Illinois Natural History Survey. “That is the stuff that was on the surface that captured the sun’s energy, and when it died, it kept some of the energy when it fell into a sinkhole and washed into the cave.”

Microorganisms such as fungi break down the surface debris, and then invertebrates such as isopods and amphipods feed on it. Salamanders may then feed on the isopods.

Sometimes other critters find their way in too — and can’t get out.

Taylor says he once found a snapping turtle inside a cave.

“You might find something that had a tragic day that fell into the cave when a sinkhole pond collapsed,” he says. “It is going to die unless it is washed out at the spring at the other end. It will end up feeding the cave.”

Conservation efforts to protect the fragile cave environment start with good environmental practices on the surface.

“The main point that I would emphasize is that anything that goes into the sinkhole also goes into the cave,” Taylor says. “And that includes sewage, pesticides and anything thrown into the sinkhole.

“Because it’s an open hole, it's like dropping something into a storm sewer,” Taylor says.

Leaking septic tanks, for example, can contribute extra nutrients to the cave system.

“One of the biggest problems is that these animals are adapted to a relatively low energy environment,” Taylor says. “Lots of extra waste or plant material enriches the cave environment.”

That’s bad news for the animals that are restricted to the cave and its usual low-energy environment. Extra fuel means that some organisms adapted to living in or out of the cave now can move in to stay.

Then they compete with those that have no other option but to make a living in caves like Illinois Caverns.

Troglophiles can live in a cave but don’t have to, Taylor says. They lay more eggs and have a faster life cycle because there is more energy available. They then become more dominant, pushing out the troglobites, those restricted to caves that are adapted to breeding at low energy levels. That means they don’t produce as many young as quickly.

The federally endangered Illinois cave amphipod is known from only a handful of caves.

“When you have lots of nutrients like sewage washed into the cave, the Illinois cave amphipod is less competitive relative to the other amphipod that you can find in springs on the surface,” Taylor says.

Taylor says cave organisms are fascinating but rarely capture the public’s imagination. He has recently started to study springtails, another cave invertebrate.

“Springtails have very little charisma,” he says with a laugh. “It’s the problem with working with invertebrates,” he says. “They don’t have the cute factor.

“But they represent the fabric of life, the diversity of life.”

Who’s down there?

An amazing array of creatures lives in Illinois Caverns.

For most of them, think small.

“You might find three or four bats, maybe three salamanders, a couple of frogs,” says biologist Steve Taylor with the Illinois Natural History Survey in Champaign.

“Cave crickets, three or four amphipods, two isopods, four or five aquatic worms,” he says, ticking off a mental checklist. “There would be earthworms, four or five mites, five or 10 springtails and 30 to 40 bacteria, if not many more — maybe hundreds.

 “You could expect the same range for fungi, with anywhere from eight to 10 species to hundreds.”

A recent trip through the caverns turned up a fungus growing on a rock that Taylor says was probably spreading out in search of sustenance.

“It maybe has eaten whatever it is on, and now is spreading out to find some other source,” Taylor says. “Springtails could feed on that fungus. So the fungus is also a food source.”

At least four or five species of flies might be found closer to the entrance. Occasionally a moth species or two will be seen. Mice also nest in the entrance or twilight zone of the cave.

Some plants grow until they exhaust the energy in their seeds. Seedlings occasionally sprout from seeds washed into the cave.

“If you find really old seedlings, you can see little fungi on them or may be a little fly or mite on them,” Taylor says.

“There is a tiny world there for those that want to look close.”

Chris Young can be contacted atchris.young@sj-r.com or (217) 788-1528.