Lechuguilla Cave is a limestone cave in the back country of Carlsbad Caverns National Park in the Guadalupe Mountains of south-eastern New Mexico. With 244.80 km (152.11 mi) of surveyed passage it is the ninth-longest explored cave in the world, and its measured depth of 484.2 m (1,588.6 ft) makes it the seventh-deepest cave in the United States. It was dissolved from below by sulfuric acid, not by rainwater from above, which left it lined with gypsum, sulfur and formations rarely seen elsewhere, and only approved scientists, surveyors and park staff may enter. The living things that define Lechuguilla are as unusual as its rock: a desert agave gave it its name, bats left the guano that first drew miners to its entrance, and in its sealed deep passages live sulfur-oxidising microbes and an ancient bacterium already resistant to modern antibiotics. This guide takes them one by one.
Agave lechuguilla in Lechuguilla Canyon: The Plant Behind the Name
The cave takes its name from the canyon through which it is entered, and the canyon takes its name from Agave lechuguilla, a plant found only in the Chihuahuan Desert. That desert covers about 501,896 km² (193,783 sq mi) of northern Mexico and the south-western United States, which makes it the largest hot desert in North America, and lechuguilla is one of its indicator species, growing on the calcareous soils that limestone country like the Guadalupe Mountains provides. In Chihuahua the name means “small lettuce”, a gentle label for a plant whose long, rigid leaves end in points hard enough to pierce leather and are known as shin-daggers.
The plant spreads mostly through underground offshoots, building large colonies across the slopes. It flowers only once, at any age from 3 to 21 years, sending up a leafless stalk that can reach 3.7 m (12 ft), and dies after blooming between May and July. The botanist Charles Wright first collected it in 1849 and John Torrey described it in 1859. Collared peccaries, or javelinas, eat it heavily in some areas, and insects, bats and birds feed on its flowers. Above the cave, this desert surface is protected as wilderness: about two-thirds of the park was set aside when the Carlsbad Caverns Wilderness was created on 10 November 1978, and Lechuguilla lies beneath it.
Bat Guano at Misery Hole: The Cave Before May 1986
For most of the 20th century Lechuguilla was a minor historic site. Its entrance was a 27 m (90 ft) pit called Misery Hole, which led to about 122 m (400 ft) of dry, dead-end passages. What made it worth visiting at all was bat guano. Small amounts were mined from the entrance passages for about a year under a mining claim filed in 1914, a sign that bats had once roosted there in numbers.
Bats are the best-known wildlife of the park as a whole. Seventeen species live there, and the most numerous is the Mexican free-tailed bat, which roosts in nearby Carlsbad Cavern from April or May until late October or early November. Its population was once estimated in the millions and has fallen sharply, with organochlorine pesticides such as DDT and dieldrin a likely cause, though a 2009 Boston University study questioned whether millions ever lived there. A thermal-imaging count in 2005 put the peak at about 793,000 bats. The natural entrance of Carlsbad Cavern is also an Important Bird Area for its colony of cave swallows, possibly the largest in the world, and at Rattlesnake Springs, a detached part of the park, more than 300 bird species have been recorded.
It was air, not animals, that revealed what lay below Misery Hole. In the 1950s cavers heard wind roaring up through the rubble on the cave floor and concluded there had to be more passage beyond. In 1984 a group from the Colorado Grotto led by Dave Allured won permission from the National Park Service to dig, and on 25 May 1986 they broke through into large walking passages. Since then explorers have mapped the cave to its present length.
Sulfur-Oxidising Microbes and the Chandelier Ballroom
Below the guano-stained entrance, Lechuguilla is a world without daylight, and its most important inhabitants are microscopic. The rock around them began as a reef. About 250 million years ago this part of the Guadalupe Mountains was the coastline of an inland sea, and the remains of sponges, bryozoans and other organisms built the Permian reef that now forms the mountains. Lechuguilla is the first cave known to extend deep enough into the range for scientists to study five separate geological formations from the inside.
Its passages were not carved by ordinary rainwater. Hydrogen sulfide rose from oil deposits deep below, met oxygen in the groundwater and formed sulfuric acid, which dissolved the limestone from the bottom up. Gypsum is a by-product of that reaction, and the cave is full of it, along with lemon-yellow sulfur. The results include gypsum chandeliers and gypsum hairs and beards up to 6.1 m (20 ft) long, soda straws of 4.6 m (15 ft), hydromagnesite balloons, cave pearls, subaqueous helictites, rusticles and U- and J-shaped loops. In size, depth and variety of formations it surpasses nearby Carlsbad Cavern, although no room yet found in Lechuguilla is larger than Carlsbad’s Big Room. Our guide to cave formations explains how stalactites and helictites grow.
Living on these minerals are rare chemolithoautotrophic bacteria, organisms that draw energy from chemical reactions rather than from organic food. They feed on sulfur, iron and manganese minerals, and they may help enlarge the cave and shape some of its odd speleothems. The BBC series Planet Earth, whose “Caves” episode aired on 22 April 2007 and featured the Chandelier Ballroom, claimed that these bacteria take no energy from the sun. That is not quite right: the sulfur-oxidising bacteria use atmospheric oxygen, produced ultimately by sunlight-driven photosynthesis, as their electron acceptor, while their energy source is hydrogen sulfide dissolved in groundwater. The microbiologist Hazel Barton, who studies how cave microbes survive on very little food, descended into Lechuguilla in October 2016 to film a sequence for the National Geographic series One Strange Rock.
Paenibacillus in Lechuguilla: Antibiotic Resistance Four Million Years Old
Lechuguilla’s deep passages are so isolated from the surface that their microbes offer a rare look at bacteria that have never met the antibiotics people have used since the 20th century. Yet a strain of Paenibacillus, a genus of spore-forming bacteria separated from Bacillus in 1993, isolated from soil samples in the cave and estimated to be about four million years old, was found to be naturally resistant to many modern antibiotics, including daptomycin. Other bacterial strains from the cave carry novel pathways for antibiotic resistance.
These finds are cited as evidence that antibiotic resistance is ancient and widespread in bacteria, not simply a product of modern medicine. Other studies also suggest that microbes from the cave may have medicinal value of their own. All of this depends on the cave staying clean, which is why every trip follows strict rules and access is limited to approved scientific researchers, survey and exploration teams, and National Park Service management trips.
Oz, Munchkinland and the Kansas Twister: Survey and Protection Since 2012
Exploration still adds new habitat to the map. In May 2012 a team led by Derek Bristol of Colorado climbed more than 120 m (410 ft) into a dome and found a new section of pits, passages and large rooms, which they named Oz. Its largest room, Munchkinland, is about 180 m (600 ft) long and up to 46 m (150 ft) wide and high, and a pit named the Kansas Twister drops more than 160 m (510 ft) from floor to ceiling, the deepest pit yet discovered in the park. The team spent eight days mapping Oz, the largest single addition to the survey since 1989, bringing the total to 216.6 km (134.6 mi). Lechuguilla held the title of deepest known cave in the United States until Tears of the Turtle Cave in Montana was explored in 2014.
Carlsbad Caverns National Park, established in 1930, became a UNESCO World Heritage Site in 1995. Filming inside Lechuguilla has always been tightly controlled: the Denver Museum of Nature and Science made one of the first documentaries there, Lechuguilla Cave: The Hidden Giant, in 1987, the National Geographic Society filmed much of its 1992 programme Mysteries Underground in the cave, and the Planet Earth team took two years to obtain permission. The biggest threat comes from outside the boundary. Lechuguilla’s passages may extend beyond the park into neighbouring Bureau of Land Management land, where oil and gas drilling has been proposed, and any leak of gas or fluid into the cave could kill cave life or cause explosions. The same oil reserves whose hydrogen sulfide once dissolved the cave could now endanger the microbes it shelters. For the show-cave side of the park, with its bat flights and the Big Room, see our Carlsbad Caverns geography guide, and for how Lechuguilla’s 244.8 km compares with the giants of Kentucky and Mexico, read our list of the longest caves in the world.