There is something comforting about burrowing deep into the Earth. It’s like renouncing the modern world’s stimulations to return to a dark, simple past. As I go deeper into Planina Cave, Slovenia’s largest water cave — a four-mile-long stunner whose lakes and dripstones are home to 60 aquatic and 40 land species — the feeling of returning to a primordial way of being intensifies.
The scientists who have taken me to the Planina Cave have dressed me in a red caving suit and a hard hat with a flashing light on top. They wear the same. I feel like a Mediterranean blonde coal miner with a French manicure. We cross a tight path that Italian soldiers, ready for death, built during World War I to ambush the Austrian enemy. Our mission today is less dire, though still noble.
We are searching for olms, the blunt-snouted, long-bodied, short-limbed, creepy-cutesy, eel-like creatures God forgot to draw eyes on. These ancient versions of a salamander, usually about 8 to 12 inches long, diverged from other amphibians almost 110 million years ago, around the same time modern birds emerged. Slovenian olms live exclusively in subterranean caves in the Dinaric Alps, a mountain range of extreme biodiversity and a natural bridge between the Balkans and the Alps.
Technically, olms do have eyes. They are just underdeveloped and covered by a layer of skin, an adaptation to the animal’s pitch-dark surroundings. Olms cultivate other senses to compensate for their blindness. They have chemoreceptors that help them catch their prey (mainly snails, insect larvae, and crustaceans), electroreceptors that allow them to detect electrical fields, and a powerful sense of smell and hearing.
Olms can gulp down their food and store nutrients in their livers, no heartburn whatsoever. They can go without food for up to 12 years, reducing their metabolic rate and entering a sort of self-cannibalization state, reabsorbing their own tissue. They can live more than 100 years, reproduce up to age 80, and fully regenerate damaged limbs and organs. They live a bit like Peter Pan: They won’t let go of the frilly gills and tail fins they had when they emerged from their eggs. Olms might be a little lazy as well. They can go years without moving. In January 2020, scientists announced that a wild olm had remained stationary for seven years before “reanimating.”
Olms have bewitched the Slovenian soul for centuries. They once appeared on a Slovenian coin. The Slovenian word for olm, človeška ribica, means “human fish.” But when Slovenian peasants encountered olms in the late 17th century, after heavy rains flushed them into surface pools, they thought that the pinkish pale creatures with the translucent skin were “baby dragons,” a high compliment. To understand the national fascination with dragons, look at Ljubljana, the Slovenian capital: Dragons, dragons everywhere, including the four copper dragon statues on the city’s iconic Zmajski Most, or Dragon Bridge.
Now, olms are bewitching biologists as well. “The olm is one of the longest-lived vertebrates, considering its low body mass — and this in combination with only negligible signs of aging,” says University of Ljubljana biologist Rok Kostanjšek. And if scientists can pinpoint the genes that allowed these amphibians to adapt so well to their cave environments, the benefits for humans could be tremendous.
Extreme adaptations in animals usually leave a mark on their genome, explains James Monaghan, a biologist at Northeastern University who is investigating the regenerative properties of the olm’s amphibian cousin, the axolotl salamander of Mexico City’s Lake Xochimilco. “Those same genes and those same pathways that lead to eyesight or to metabolism or pigmentation are the same in humans as they are in olms,” Monaghan says.
So cracking the olm’s genetic code — as the researchers I’m olm-hunting with today are endeavoring to do — could unlock secret recipes for fighting eye disease and obesity, enduring starvation, reproducing at an older age, or even extending the human lifespan.
I’m olm-hunting with Peter Trontelj and Hans Recknagel, evolutionary biologists at the University of Ljubljana, and Špela Borko, a subterranean biologist and researcher at the university. All of them came to the olm through some combination of scientific drive and adventurous spirit.
A seasoned cave researcher, Trontelj, 55, first took up caving in high school. During the Ten-Day-War, or Slovenian War of Independence, in summer 1991, he served as a cave rescuer taking care of bomb shelters. Though he got his bachelor’s degree in birds and wrote a dissertation on leeches, he couldn’t escape the olm’s allures. “Instead of teddy bears, we grow up with olms,” he says.
Recknagel, 37, from Ibbenbüren, Germany, was fixated on reptiles, frogs, salamanders, and dinosaurs from a very young age. He even kept a frog as an imaginary friend and attributed “divine powers” to it. Olms, with their subterranean adaptations and extraterrestrial unfamiliarity, fit the same mold, he said. “I would literally beg my parents to bring me here to see the olm,” he says.
In 2017, Recknagel met Trontelj and Kostanjšek at a herpetology conference, where they presented their work on the olm. He immediately wrote to them and a collaboration began. It starts with mapping the olm genome, which they’re doing with partners from Denmark and China and funding from the Marie Sklodowska-Curie Foundation and the Slovenian Research Agency.
To decipher the olm genome, which is about 16 times larger than a human’s, researchers will need DNA from hundreds of samples. They have already discovered nine potentially different species of olm, each of which evolved similar characteristics independently in the watery abyss. Eight are variations on the bleached, sightless white olm of Slovenian lore. There’s also a black olm, which has slightly bigger eyes, is less evolved than its kin, and was discovered less than 40 years ago, according to Trontelj.
Long and slippery, the black amphibian dives out of the net and expertly lands on the ground. A giant by olm standards, the creature is a foot long and weighs about 2 ounces.
Truth be told, the University of Ljubljana trio is not very confident about our endeavor today. Heavy rainfall preceded my visit to the Slovenian capital, which means that the groundwater level is simply too high for us to trudge through the water in the hopes of catching an olm. The scientists are carrying neoprene suits and scuba fins for dives into the underground rivers, as well as fishing nets, scales, containers to put the olms in, and a DNA-sampling kit. Fortune favors the brave, so we march on.
Olm-hunting requires scientists to develop cave-diving skills. Some Slovenian caves reach a staggering depth of 1.2 miles, and their many physical obstacles require skills called, in climbing parlance, “technical climbing.” In 2019, Borko, now 32, and four other female scientists spent five days exploring a cave more than a half-mile below the surface.
In Planina Cave today, we take a half-mile stroll to the confluence of two underground rivers, which involves a good amount of climbing up and down slippery rocks and delving into tight spaces. In its humid serenity, the cave does not rattle me at all. But I see signs that the landscape is under threat — and with it, the olm, too. Trontelj points at what seems like a conglomerate of bubbles at the water’s edge. It is polluted water, a mixture of badly treated wastewater, agriculture fertilizers, and pig-farm manure. They permeate the surface soil and contaminate the groundwater, eventually reaching the underground caves.
Then, there is climate change. Historic floods that used to happen only once a century will be appearing more frequently and hitting Slovenia harder, Trontelj says. Groundwater levels rise steeply in such events, flushing olms out of the water and onto the surface, where lethal sunburns and predators like birds and fish await them. There’s more, he adds, that climate change may do: “Long-lasting dry periods shrink the olm’s natural habitat or make it vanish altogether. Pollutants concentrate from sub-lethal to lethal levels … Natural cycles that are needed to initiate the reproductive period get disrupted. Pathogens and parasites become more abundant. General stress increases.”
Trontelj puts on his diving suit and plunges into the Pivka River, a 16-mile-long river ending in Planina Cave, to look for olms hiding in the underwater crevices. Alas, the olms won’t cooperate. The team decides to try its luck at night.
That evening, Recknagel takes me to the springs of Bela Krajina, or White Carniola, 55 miles southeast of Ljubljana, near the border with Croatia. Bela Krajina is fertile olm-hunting waters; the black olm was discovered there in the 1980s. Apparently, olms are easier to catch at night, as they no longer go incognito inside the cushion of the water but step out of it to feed themselves. The two-hour ride in the dark doesn’t afford me great views of the fairytale-like land, covered by ferns and white birches. But this second olm-hunting round will pay off.
We approach a protected spring, which has been enclosed in a hut built by the University of Ljubljana to observe and study the animals without disturbing them. Recknagel has the key and opens it. As soon as we enter the spring, I hear Recknagel exclaim, “There it is! Do you see it?”
I don’t, but I trust something good is happening when he says, “I’m going to catch it.” He carefully climbs down a knoll to the small spring, with a fishing net in hand. It doesn’t take long for him to give out an “Oh, yes!” as the maneuvers of his net trap an olm — perhaps the biggest he has ever caught. Long and slippery, the black amphibian dives out of it and expertly lands on the ground the first time Recknagel attempts to weigh it. A giant by olm standards, the creature is a foot long and weighs 50 grams, or about 2 ounces. Recknagel is excited to have caught a black olm that’s so large. “We caught one of the biggest and rarest olms,” Recknagel says.
Scientists name the olms they catch in the field. Each name consists of the first three letters of the name of the place where the olm was retrieved and a number that notes whether the salamander was the first, second, third, and so on to be located there. So this particular creature is named JEL01, the first of its kind to appear in Jelševnik, a settlement in White Carniola.
Recknagel dons special gloves to protect the olm from human-transmitted infections and takes a swab from its skin. He takes pictures of the olm to study its coloration and extracts a tissue sample. The procedure seems slightly inconvenient for the animal, which is hardly moving: it appears to have adopted an “I-am-already-dead-leave-me-alone” survival strategy to outsmart the intruders. “Two centimeters at most,” Recknagel says about the tissue sample, which will be crucial for the in-lab DNA and RNA study.
Later, Recknagel catches a white olm in a nearby spring and follows the same scientific protocol. Then the olms are released into the spring so they can resume their cryptic, long lives in peace. Almost as soon as they’ve been let go, they disappear into the crevices.
The olm can seem like a creature from a magical world, but the commonalities between its genetic code and ours drive researchers to place their tissue samples under powerful microscopes. “What led to the loss of eyesight in the olm was most likely a few changes in the genome,” says Northeastern’s Monaghan. “By identifying one or a handful of genes that contributed to the loss of eyesight, you can inform human medicine, too. It’s a super-clever approach.” By mapping the olm’s genetic code, scientists aim to unlock all of the genetic changes that give the olm the ability to withstand starvation, navigate the abyss, regenerate its limbs, and reproduce at an old age. Scientists could potentially create a curated database of candidate human genes associated with all the above.
That said, it’s not the olm or nothing. Nature has other very-long-lived species ripe for study: giant tortoises, red sea urchins, bowhead whales, freshwater pearl mussels, tubeworms. It also has the African turquoise killifish, which lives a meager four to nine months. “It’s equally important. We need to study short-lived species also to gain insights into longevity,” Monaghan adds. The olm is just a piece of the puzzle.
Perhaps the Slovenian research and the cumulative body of work on “baby dragons” will bequeath longevity and insights into well-being to future human generations. Unlike the olm, I wouldn’t want to remain blind and immobile for seven years. But who will ever truly know the olm’s inner life?