(CNN) – Postojna Cave, located an hour’s drive southwest of Ljubljana, the capital of Slovenia, is so vast that it has its own railway.
Still, one of the cave’s main attractions is something on the other end of the size spectrum – and completely unique to Postojna.
It has been known to locals for centuries and has graffiti, dated 1213, to prove it. Tourists began to arrive in large numbers after an 1818 inaugural visit by Francis I of Austria, the last Holy Roman Emperor of Europe. About 35 million followed in its wake.
It’s easy to see why. The cave is so large that a small train travels the first two of its 24 kilometers of network of underground chambers and tunnels.
The railway line ends in the imposing Congress Hall where the Milan Symphony Orchestra performed in 1930. From there a pedestrian path crosses six geological layers, crosses a bridge over a chasm built by Russian prisoners during the First World War and continues beyond the underground cliffs and gorges, stalactites thin as spaghetti and curtains of flows.
Traveling to a depth of 115 meters (377 feet), it sometimes leads visitors through cracks only one meter wide.
Yet the real adrenaline rush is spared to come 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 Postojna Cave D. D
Elms, or proteus anguinus in Latin, are blind salamanders, about 25 centimeters long, which never develop beyond their juvenile, watery phase.
Locals nicknamed them baby dragons because they were taken away from Postojna during the floods, and as the caves are home to the dragons, surely these were their babies, right?
Nowadays, visitors can meet them as they swim among the rocks in a purpose built aquarium deep inside the cave.
“Cute aren’t they?” asks Mateja Rosa, a big fan of Olm, who works as marketing and PR manager of Postojna.
I really am. In appearance almost toy, they are also sometimes referred to as human fish because, despite living underwater, they have smooth pinkish-white skin instead of scales and cartoon-fingered limbs under their busy red gills.
They may be blind, but the offspring seem to hear the approach of visitors, apparently sensitive to vibrations. One even sticks to the glass tub near where it scans my face.
It’s curious? Is it being friendly?
Not so, according to Primož Gnezda, an enthusiastic young biologist who has been studying these creatures for years.
“The elms in the cave tank hear you, get scared and take their safe positions,” says Gnezda during a tour of the Vivarium, an exhibition space near the cave that displays more elms and a slew of other Postojna creatures.
The seemingly friendly olm is known for his unusual behavior, but he was not sociable.
“It always spreads against the glass for safety,” says Gnezda. “That he 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, offspring can live up to 100 years and survive for a long time without eating.
“Seven years for sure,” he says. “For the first two or three years, no problem. Then they start to lose weight, stop moving and just wait for the prey to pass. More than seven years and some can die, some can survive, depending on the individual’s metabolism. . “
When they find food, we can forgive their good manners.
“We feed them the worms,” says Gnezda. “The worms form a small ball together in the water and the offspring come to suck it whole like a vacuum cleaner. Sometimes they eat so violently that you can see the worms coming out of their gills along with the water.”
The Vivarium leads to the laboratory where scientists are licensed to hold 10 olm for research. A lot of money is spent on these creatures.
“The biologists studied their DNA,” says Gnezda. “Their genome is like a novel. It’s 16 times longer than 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 confused and we have to reconstruct the story.”
Is there a reason we’re so interested?
“Their regenerative power is amazing. If they lose a limb, they grow it back. The idea of research is to discover the mechanism behind it.”
“Not to regrow your arm or leg, but perhaps to produce a new human hand or leg from your own cells within a laboratory and then graft it onto you. This is, of course, very, very much in the future.”
Offspring can live up to 100 years.
Jure Makovec / AFP / Getty Images
Since offspring are cute, don’t need to be fed, and will likely outlive you, Rosa says they were sometimes given as pets to visiting dignitaries in the past.
“Most of them are dead,” he adds. “The elms need to be kept at a temperature of around 13 degrees Celsius (55 F). If the temperature rises rapidly, say 10 to 15 C, it kills them.”
Salamanders begin their life in the water like prolimi, but then drop their gills, develop lungs, walk on land and mature sexually; yet the offspring remain and multiply in the juvenile stage – a biological oddity like their close relative the axolotl, also nicknamed the Mexican walking fish.
Elms even have a mating dance.
“That’s how it goes,” says Gnezda. “When the female is ready, she will come to the male. When he sniffs her, he will start swimming in front of her; she will follow him and do a few laps together.
“At some point the male will leave a package of sperm on the floor. He will take it and put it in a pocket inside her. When an egg comes out, it will be fertilized by itself.”
And that’s not all.
“You can’t tell if an olm is male or female from their DNA. Both male and female have the same chromosomes. We are now trying to differentiate between the sexes by analyzing their blood and checking hormonal relationships. It looks promising but that’s still it. a research in progress “.
Biologist Primož Gnezda is among the scientists who study offspring.
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 if they approached her; to the delight of the researchers, they saw that he was protecting an egg.
His comrades were immediately removed and his tank was isolated. Infrared cameras revealed that she continued to spawn for another eight weeks.
“In the end it produced 64 eggs,” Gnezda says. “In nature the mother attacks the eggs on the rocks, because there is no real predator out there in the cave.”
“But many things can go wrong while the egg is developing and about two-thirds of the hatchlings die on their own.”
Exactly four months after the first egg was laid, the first baby dragon was born. He pushed himself out, fell to the bottom of the aquarium, and then swam precociously around.
In all 21 survived. Curiously, they are born with eyes that they keep for several years until the skin grows on them and makes them blind.
And as of June 2021, two of those five-year-old offspring are now on display.
As Gnezda reveals during a visit to the Vivarium, they are not the only unusual occupants of Postojna.
There are cave crickets that eat their limbs if they can’t find food; venomous cave centipedes; thin-necked beetles whose wings have atrophied and merged on the abdomen; cave shrimp, the offspring’s favorite snack; and the obligatory chilling spider: Since there are no flying insects inside the cave, the spiders use their silk to weave cocoons rather than webs.
Speaking of food, when the proteus were swept into rivers by floods, did they ever end up on someone’s plate?
Yes, says Rosa. “Until the 1980s they were sold grilled in Trieste fishmongers”.
“They taste like bland squid. Or so I’m told.”