Now, large crowds from all over the world have been queueing up to witness the extremely rare hatching of the mysterious olms — ancient underwater predators that can live up to 100 years and only breed once in a decade.
Their treat came Tuesday when the translucent larva broke through the delicate egg envelope after four months of nervously monitored gestation
The birth, caught on live camera, is nothing short of “a miracle”, cave spokesmen said.
“A mere two baby olms successfully hatch from 500 eggs in nature,” they said in a jubilant statement.
Found primarily in Balkan cave rivers, the protected eel-like species has been living in the world-famous Postojna cave, 50 kilometres (30 miles) southwest of the capital Ljubljana, for what researchers say is millions of years.
This week, the tourist attraction became one of the first ever human-controlled environments to successfully breed a baby olm.
“Although both science and researchers’ previous experience gave us almost zero chance that the drama unfolding in the cave aquarium before our very eyes would have a happy ending… we had faith it would happen,” the cave statement said.
The good news doesn’t end there: the new arrival could soon be joined by several siblings, with more eggs set to hatch at any moment.
– No food for 10 years –
Inside a giant hall, the mother and her precious spawn are kept in complete darkness in a covered tank under the continuous watch of a night-vision camera.
On a nearby television screen, visitors can see the miniature eggs spread over a rock. From time to time, one of the embryos stirs ever so lightly.
“It’s one of those moments where you are happy to be alive now and experience such a unique event,” said Saso Weldt, a biologist working at Postojna, one of Europe’s largest caves that draws 700,000 visitors a year.
Weldt and his team hope the new arrivals will help to shed fresh light on the enigmatic olm, which has become a national symbol and even featured on Slovenia’s currency before the euro was introduced.
While locals now fondly talk of their “baby dragons”, people for centuries were too afraid to even go near the cave.
During winter, heavy rains would wash out the wriggly creatures from the grotto as it lay surrounded by a sea of thick fog, according to 17th century folk tales.
Slovenians believed them to be the offspring of fire-breathing “dragons living inside the dangerous cave”, explained Weldt.
Reaching a maximum length of 35 centimetres (13.5 inches), the blind animal with its four tiny limbs is a far cry from the scary monsters conjured up in national folklore.
Sometimes also referred to as “human fish”, the slim vertebrate sports has pink three feathery gills on each side of its elongated snout. The body’s sheer pink skin makes it easy to spot the internal organs.
But its cave-dwelling existence has also equipped the olm with some extremely powerful skills.
In place of sight, it has developed acute sensory receptors for smell and movement, helping it to hunt for prey like crabs and snails in the dark, or snap at intruders.
Even more impressively, the small predator can go without food for up to a decade.
– ‘Flagship species’ –
Breeding olms is a difficult and often fatal affair. A previous try in 2013 failed to produce any fertilised eggs at Postojna.
But the latest attempt looks more promising.
Of the 64 eggs laid in January, two dozen remained alive, with their gills functional and their hearts clearly beating.
For those who make it, the path to adulthood will be long: “They will take around 10 to 15 years to reach their full size,” noted Weldt.
And even then, their long-term survival is not guaranteed.
Although not officially endangered, the species is nevertheless considered vulnerable as it finds itself at risk of environmental changes like pollution seeping into the so-called karsts, or caves created from water eating through soluble rocks like limestone.
“Olms are a flagship species need of protection. If there’s too much pollution, they will disappear,” warned Weldt.