(DailyExpertNews) — Postojna Cave, an hour’s drive southwest of Slovenia’s capital Ljubljana, is so large that it has its own railway.
And yet one of the main attractions of the cave is something on the other end of the size spectrum – and completely unique to Postojna.
It has been known to the locals for centuries and has the graffiti, dated 1213 to prove it. After an inaugural visit in 1818 by Franz I of Austria, Europe’s last Holy Roman Emperor, tourists arrived in droves. About 35 million have followed in his wake.
It’s easy to see why. The cave is so large that a small train runs for the first two of the 15-mile network of underground chambers and tunnels.
The train line ends at the huge Assembly Hall where the Milan Symphony Orchestra performed in 1930. From there, a hiking trail cuts through six geological layers, crosses a bridge over a gorge built by Russian prisoners during World War I, and continues past subterranean clifftops and gorges, spaghetti-thin stalactites, and flowstone curtains.
It travels to depths of 115 meters (377 feet), at times taking visitors through fissures as small as one meter wide.
And yet the real adrenaline rush is saved from coming face to face with the wacky creatures found in the Postojna cave system and nowhere else on Earth.
Elms grow up to 25 centimeters in length.
Courtesy of Postojna Cave D. D
Olms, or proteus anguinus in Latin, are blind salamanders, about 25 centimeters long, that never develop beyond their juvenile, watery phase.
The locals called them baby dragons because they were washed away from Postojna during floods and since caves are the abode of dragons, surely these were their babies?
Today, visitors can see them swimming among the rocks in a purpose-built aquarium deep within the cave.
“Nice right?” asks Mateja Rosa, a big olm fan, who works as Postojna’s marketing and PR manager.
Indeed they are. They look almost toy-like and are sometimes referred to as human fish because – despite living underwater – they have pinkish-white, smooth skin instead of scales, and limbs with cartoon-like fingers under their busy red gills.
They may be blind, but the elms seem to hear the approach of visitors, apparently sensitive to vibration. One even clings to the glass tank near where my face peers in.
Is it curious? Is it friendly?
Not so, according to Primož Gnezda, a young, enthusiastic biologist who has been studying these creatures for years.
“The olms in the cave tank hear you, get scared and take their safe positions,” Gnezda says during a tour of the Vivarium, an exhibition space adjacent to the cave that showcases more olms and a slew of other Postojna creatures.
The apparently friendly olm is known for its unusual behavior but was not sociable.
“It always spreads against the glass for safety,” Gnezda says. “That it appeared next to your face was just a coincidence.”
Visitors to Postojna can see elms in an aquarium.
Jure Makovec/AFP/Getty Images
According to Rosa, elms can live to be 100 years old and survive long periods without eating.
“Seven years for sure,” she says. “It’s not a problem for the first two to three years. Then they start to lose weight, stop moving and just wait for prey to pass by. Over seven years and some can die, some can survive, depending on the condition.” metabolism of the individual.”
If they find food, we can forgive their manners.
“We feed them worms,” says Gnezda. “The worms together form a ball in the water and the elms come to suck it all up like a vacuum cleaner. Sometimes they eat so vigorously that you see worms coming out of their gills with the water.”
The Vivarium leads to the lab where scientists are licensed to keep 10 olms for research. A lot of money is spent on these creatures.
“Biologists have examined their DNA,” Gnezda says. “Their genome is like a novella. It’s 16 times longer than the human and more complicated.”
“You also have a lot of empty spaces. We don’t know why they exist. Imagine a 600 page book where all the words are jumbled and we have to reconstruct the story.”
Is there a reason why we are so interested?
“Their regenerative power is amazing. If they lose a limb, they regrow. The idea of the research is to figure out the mechanism behind it.”
“Not to actually grow your arm or your leg back, but maybe to make a new human hand or leg from your own cells in a lab and then graft it onto you. Of course, that’s far, far in the future.”
The elms can live up to 100 years.
Jure Makovec/AFP/Getty Images
Since the olms are cute, require no feeding, and will likely outlive you, Rosa says they were sometimes given as pets to visiting dignitaries in the past.
“Most died,” she adds. “Olms should be kept at about 13 Celsius (55 F). If the temperature rises quickly, say from 10C to 15C, they will die.”
Salamanders begin life in the water as elms, but then drop their gills, develop lungs, walk on land and become sexually mature; but elms remain and multiply in the juvenile stage – a biological idiosyncrasy like their closest relative the axolotl, also known as the Mexican walking fish.
Olms even have a mating dance.
“It goes like this,” says Gnezda. “When the female is ready, she will come to the male. If he smells her, he will begin to swim in front of her; she will follow him and make a few circles together.
“At some point, the male will leave a packet of sperm on the ground. She picks it up and stores it in a bag inside her. When an egg hatches, it fertilizes itself.”
And that’s not all.
“You can’t tell from its DNA whether an olm is male or female. Both the male and female have the same chromosomes. Now we are trying to distinguish between sexes by analyzing their blood and checking the hormone ratios. It looks promising , but this is still an ongoing investigation.”
Biologist Primož Gnezda is one of the scientists studying the olms.
Jure Makovec/AFP/Getty Images
Now to the big announcement.
On January 30, 2016, a female began to feel very territorial and attacked the other elms as they approached her; much to the delight of the researchers, they saw that she was guarding an egg.
Her companions were immediately removed and her tank was isolated. Infrared cameras showed that she continued to lay eggs for another eight weeks.
“She ended up producing 64 eggs,” Gnezda says. “In nature, the mother sticks the eggs on rocks, because there is no real predator in the cave.”
“But a lot can go wrong while the egg is developing and about two-thirds of the fry just die on their own.”
Exactly four months after the first egg was laid, the first baby dragon hatched. It stuck out, fell to the bottom of the aquarium, then swam around early.
Altogether 21 survived. Intriguingly, they are born with eyes that they keep for several years until skin grows over them and they become blind.
And since June 2021, two of those five-year-old olms are now on display.
As Gnezda reveals during a tour of the Vivarium, they are not the only unusual inhabitant of Postojna.
There are cave crickets that will eat their own limbs if they can’t find food; poisonous cave millipedes; slender beetles whose wings are atrophied and fused on their bellies; cave shrimp, the olm’s favorite snack; and the obligatory blood-curdling spider – since there are no flying insects in the cave, spiders use their silks to weave cocoons instead of webs.
Speaking of food, when floods washed the olms into rivers, did they ever end up on anyone’s plate?
Yes, says Rosa. “Until the 1980s, they were sold on the mat in the fish markets in Trieste.”
“They taste like bland calamari. At least that’s what I’ve been told.’