(CNN) – Postojna Cave, located an hour’s drive southwest of Ljubljana, the Slovenian capital, is so large that it has its own railway.

However, one of the main attractions of the cave is something at the other end of the range – and completely unique to Postojna.

Baby dragons!

The locals have known it for centuries and it has graffiti from 1213 as evidence. Tourists began to arrive in large numbers after the inaugural visit in 1818 of Francis I of Austria, the last European Holy Roman Emperor. He was followed by about 35 million.

It is easy to understand why. The cave is so large that a small train runs to the first two of its 24-kilometer-long network of underground chambers and tunnels.

The train line ends at the massive Congress Hall, where the Milan Symphony Orchestra performed in 1930. From there, a footpath passes through six geological strata, crossing a bridge over an abyss built by Russian prisoners of war during World War I and continuing past underground cliffs and gorges, spaghetti thin stalactites and curtains.

Traveling to a depth of 115 meters (377 feet), it sometimes takes visitors through crevices only one meter wide.

Yet the real adrenaline is spared for confronting the bizarre creatures found in the Postojna Cave system and nowhere else on Earth.

Blind salamanders

Olme or proteus anguinus in Latin are blind salamanders, about 25 inches long, that never develop beyond their youthful, aquatic phase.

The locals called them dragons because the floods washed them out of Postojna and because the caves are the abode of dragons, they were definitely their babies, right?

Today, visitors can meet them as they swim among the rocks in a purpose-built aquarium deep in the cave.

“Lovely, isn’t it?” wonders Mateja Rosa, a big fan of olma who works as a post-marketing and PR manager.

They really are. They look almost like toys, sometimes called human fish because, despite living underwater, they have pinkish-white smooth skin instead of scales and cartoon-like limbs with red gills.

They may be blind, but the olmas seem to hear the approach of visitors, obviously sensitive to vibrations. One even attaches to a glass tank near where my face looks.

Is he curious? Is he friendly?

This is not the case, says Primož Gnezda, a young, enthusiastic biologist who has been studying these creatures for years.

“The orbs in the cave reservoir hear you, get scared and take their safe positions,” says Gnezda during a visit to the Vivarium, an exhibition space next to the cave where several fish and many other Postojna creatures can be seen.

The seemingly friendly olm is known for his unusual behavior, but he was not sociable.

“For safety’s sake, it always spreads against the glass,” says Gnezda. “That it appeared next to your face was just a coincidence.”

Behavior behind the table

Visitors to Postojna can see fish in the aquarium.

Jure Makovec / AFP / Getty Images

According to Rosa, fish can live up to 100 years and can survive long periods without eating.

“Seven years for sure,” he says. “The first two to three years with no problems. Then they start losing weight, stop moving and just wait for the prey to pass. Longer than seven years and some can die, some can survive, depending on the individual’s metabolism.” “

When they find food, we can forgive them.

“We feed them with worms,” Gnezda says. “Worms together form a small ball in the water and the olives come and pick it up 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 a laboratory where scientists are licensed to feed 10 fish for research. A lot of money is spent on these creatures.

“Biologists are researching their DNA,” Gnezda says. “Their genome is like a novella. It’s 16 times longer than a human’s and more complex.”

“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 mixed up and we have to reconstruct the story.”

Is there a reason we are so interested?

“Their regenerative power is amazing. If they lose a limb, they regrow it. The idea of ​​the research is to discover the mechanism behind that.”

“Not to actually grow your arm or leg back, but maybe to make a new human arm or leg out of your own cells in the lab and then transplant it into you. That’s far, far into the future, of course.”

Mating dance

Fish can live up to 100 years.

Jure Makovec / AFP / Getty Images

Given that olmas are cute, don’t need feeding, and are likely to survive, Rosa says they used to be given to visiting dignitaries as pets.

“Most died,” he adds. “Olme should be kept at about 13 Celsius (55 F). If the temperature rises quickly, say from 10 C to 15 C, it kills them.”

Salamanders begin their life in the water like olives, then drop their gills, develop their lungs, walk on land, and reach sexual maturity; but fish remain and reproduce at a young age – a biological oddity, such as their close relative axolotl, also called the Mexican walking fish.

Olme 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 smells her, he will start swimming in front of her, she will follow him and make a few laps together.

“At some point, the male will leave a packet of semen on the ground. She will pick it up and store it in her pocket. When the egg comes out, it will fertilize itself.”

And that’s not all.

“You can’t tell from a DNA whether a fish is male or female. Both males and females have the same chromosomes. We’re now trying to differentiate between the sexes by analyzing their blood and checking hormone levels. It seems promising, but research is still ongoing.”

Hatching dragons

Biologist Primož Gnezda is one of the scientists studying fish.

Jure Makovec / AFP / Getty Images

Now to the big post.

On January 30, 2016, one female began to feel very territorial and attacked other sheep if they approached her; to the delight of the researchers they saw that she was guarding the egg.

Her companions were immediately removed and her tank insulated. Infrared cameras showed she had been laying eggs for another eight weeks.

“In the end, she produced 64 eggs,” Gnezda says. “In nature, the mother lays eggs on the rocks, because there is no real predator out there in the cave.”

“But a lot can go wrong while the egg is developing and about two-thirds of the young die alone.”

Exactly four months after the hatching of the first egg, the first dragon hatched. It erupted, fell to the bottom of the aquarium and then swam prematurely.

There are 21 survivors. Interestingly, they are born with eyes that feed them for years until their skin grows and blinds them.

And as of June 2021, two of these five-year-old olives are now on display.

As Gnezda reveals during a visit to the Vivarium, they are not the only unusual residents of Postojna.

There are cave crickets that eat their own limbs if they can’t find food; poisonous cave centipedes; slender beetles whose wings have atrophied and grown on the abdomen; cave shrimp, a favorite fish snack; and the obligatory spider that cools the blood – because there are no flying insects in the cave, spiders use their silk to weave cocoons rather than webs.

Speaking of food, when fish floods washed into the rivers, did they ever end up on someone’s plate?

Yes, says Rosa. “Until the 1980s, they could be sold on a plate in Trieste’s fish markets.”

in?

“They taste like soft squid. Or so they told me.”