Paint Rock, Alabama — Nothing really distinguishes Nat Mountain from its hilly neighbors amid the southern foothills of the Appalachian Mountains. It's not particularly tall at 1,600 feet. It offers no sweeping summertime views, except snatches of distant mountains and the curvaceous Paint Rock River. It's home to the Fern Cave National Wildlife Refuge, but, on the surface, there's really nothing to do here.

It's what's below ground that tantalizes.

Fern Cave is considered the "crown jewel" of Alabama caves. Its 15 miles of explored passageways are the longest in the state. An estimated 1.5 million federally endangered gray bats — the largest colony in the world — winter here. A wealth of at-risk species, including the endangered Alabama cave shrimp, call Fern home. Scientists believe the cave is the most biodiverse cavern in the limestone karst region of Alabama, Tennessee and Georgia. Shelta Cave, in nearby Huntsville, currently holds the record for the most cave dependent-species in similar limestone habitat: 24.

Yet nobody has ever fully catalogued the ecological wonders at Nat Mountain. Until now.

Ben Miller, Pedro Ardapple and Ben Tobin tally species in the Lower North Cave Ben Miller of the U.S. Geological Survey (from left), Pedro Ardapple of USFWS and Ben Tobin of the Kentucky Geological Survey tally species in the Lower North Cave. (Photo: Christine Walkey/Southeastern Cave Conservancy)

Tommy Inebnit, a biologist with the U.S. Fish and Wildlife Service (USFWS), led a team of scientists and spelunkers into Fern Cave one recent Saturday morning for an all-day "bio-blitz." The goal was to tally as many fish, salamanders, beetles, snails and springtails as possible. Inebnit's team will return in September to explore Fern Cave's deepest passage before releasing a comprehensive biological inventory.

"We've owned this cave for decades and we don't know what's in there," said Inebnit, who drove from Conway, Arkansas, for the highly anticipated investigation. "The mission of these refuges is to conserve and protect the flora and fauna. We hope the bio-inventory will help the refuge in managing this very cool resource."

Off-limits to the public, but not critters

northern slimy salamander, Fern Cave National Wildlife Refuge The northern slimy salamander is not listed. (Photo: Michael Senn/USFWS)

Turn off the highway, cross the railroad tracks and follow the dirt road along the river past Holiness Baptist gospel church and a series of gates to reach the refuge. The drive is slowed by axle-bending potholes and white-tailed deer that explode from the brush lining the bottom lands. The road passes through properties owned by hunt clubs and the Southeastern Cave Conservancy, a Tennessee nonprofit dedicated to the preservation and exploration of grottoes in six states.

The cave is off-limits to the public due to its critical role as a wintertime hibernaculum for gray and Indiana bats, which are both endangered and under siege. USFWS, which established the refuge in 1981, only issues special permits to cave experts keen on inventorying and protecting the wealth of species. The 199-acre above-ground refuge, though, is open to all. Not that there's much to do here; hikers and bird-watchers must trail-blaze steep terrain covered in hickories, oaks and beeches.

"Sometimes, in caving, it's more about the journey than the destination," said Christine Walkey, the cave conservancy's outreach director, referring to what's below and not the tortuous above-ground route to reach Fern Cave. "There are cool things to see underground. The longer you look in a cave, the more you see."

Walkey and a dozen other cave-lovers gathered at the road's end to ready the 300-foot ropes, coveralls, helmets and headlamps for the descent into Fern. They scoured a topographic map of the cave's tentacled corridors. They split into teams. Many of the partners, including the Nature Conservancy, the U.S. Geological Survey and the University of Alabama in Huntsville, had been here before; all were familiar with this corner of Alabama where a bedrock of Swiss cheese limestone has created an amazing network of tunnels. Some 2,000 caves riddle the region.

"It's always a good day when you get to spend time in Jackson County," Walkey said.

Before they went down, they had to go up. Up Nat Mountain to a variety of sinkholes, waterfalls and plain old holes in the ground. Dave Richardson and crew stopped at the Surprise Pit — so named because, in 1961, it was the first entrance discovered to Fern Cave and for several years was considered the deepest vertical pit in the nation. It drops 437 feet straight down and is reached by entering a sinkhole and dipping behind a 50-foot wall of crenellated rock and falling water. A carpet of bright green ferns frames the pit's entrance. Hence the name of the refuge.

A cave salamander was spotted, as was a Southern leopard frog. Neither is at-risk; both are cute.

orange cave salamander, Fern Cave National Wildlife Refuge Cave salamanders also call this special place home. (Photo: Michael Senn/USFWS)

Richardson, a terrestrial ecologist with the service's Inventory and Monitoring Branch out of Mississippi, changed the batteries of an acoustic detector that picks up bat activity. Nobody descended Surprise Pit. Instead, Richardson's crew climbed higher up the mountain to the Johnston entrance to await Matt Niemiller's crew.

1,000 cave crickets wallowing in guano

cave crickets, Fern Cave Cave crickets are just one of the creatures that feed on bat guano in this environment. (Photo: Michael Senn/USFWS)

Niemiller, a professor of ecology at the university in Huntsville, and his team forged nose-high water at the Sump entrance to count more than 100 cave crayfish, four different species of cave isopods, four cave beetles and a wealth of other invertebrates. Their most prized discovery: the Alabama cave shrimp, an endangered, translucent and eyeless decapod crustacean.

The cavers proceeded backwards into the Johnston hole, sliding past the "cave closed" sign and into the dark. They contorted their bodies around boulders and sought purchases in nooks and crannies. In a small room, with headlamps now lit, they turned to see … a thousand creepy, crawly, antenna-wiggling cave crickets wallowing in guano. There were cave salamanders and leopard frogs too.

Further down the explorers crab-walked over rocks, down chutes and through narrow tunnels until they came to a relatively large room with luminous water droplets covering the ceiling. A southeastern cave pseudoscorpion, maybe 10 millimeters long, was dug from a wood rat's nest. Fern is home to two types of the endemic bug. Cave flatworms, spiders and springtails were also catalogued.

"The earth is so jumbled here with rocks of all sizes and shapes going every which way," Niemiller mused. "It's a seemingly inhospitable atmosphere. Yet there is life and nutrients. The guano feeds all sorts of animals."

He stopped.

"Hey guys," he said, "we got grays in here."

Upside down, attached to a waist-high overhang, sat a three-inch-long gray bat. One-hundred more, all balled together into a basketball-sized knot, clustered 20 feet away. Niemiller and crew, per endangered bat-protection protocol, moved away from the cluster. While Fern Cave is famous for its wintertime colonies of hibernating bats, a healthy sampling in the summertime is encouraging. White-nose syndrome, the fungal disease that has killed an estimated 7 million bats since detection in New York in 2006, threatens Alabama bats too. The service closed Fern Cave to the public in 2009 to minimize chances the disease would hit gray and Indiana bat colonies. But the deadly pathogen was discovered in Fern four years later on non-listed tri-colored bats. So far, the endangered bats haven't succumbed to the disease.

"I guarantee there are more bats back there," Niemiller said while motioning towards the deeper, darker sections of the Johnson entrance. "Fern Cave has just an amazing diversity of life. It's well known, of course, for bats, but it's got cave shrimp, flat-backed millipedes and over 20 obligates [cave dependent-species] which is very significant. When it's all said and done, Fern Cave will be, if not at the top of the list, one of the most diverse caves in Alabama."

Niemiller and crew retraced their steps out of the cave and headed back down hill at day's end. Kevin England, a high school teacher tasked with documenting Fern Cave's abundant flora, awaited. He identified a pelt lichen, twinleaf herb and American smoketree. (No threatened American hart's-tongue fern, though.)

The cavers stripped off muddy coveralls, shirts, pants and shoes and placed them in plastic bags to be bleached (to keep white nose fungus from spreading) and cleaned at home. Inebnit's four-man team was last to arrive. They'd rappelled 208 feet straight down into Little Morgue Pit to find a welter of species such as northern slimy salamanders, glow worms, cave isopods, springtails and mites.

By day's end, two new species had been added to the list, tying Shelta as the most biodiverse cave in the southeastern karst region. Inebnit has high hopes for the September trip to Bottom Cave.

"All we need," he said, "is one more species."

The teams climbed into their trucks, jounced back over the potholed road and headed straight to Joe's Pizza.

This story was originally written for the U.S. Fish & Wildlife Service and is republished with permission here.

Dan Chapman is a public affairs specialist with the Southeast Region of the U.S. Fish & Wildlife Service.

When it comes to biodiversity, Alabama's Fern Cave is an under-the-radar hot spot
Fern Cave hosts a wealth of species, including the largest colony in the world of endangered gray bats and many other species.