Postojna Cave in Slovenia is one of Europe’s longest cave networks and one of the world’s most spectacular subterranean tourist sites. Hundreds of thousands of visitors come here every year to gaze at its wonders: its huge stalactites and stalagmites, its curtains of coloured rock and bridges that have been carved out of the local limestone by the river Pivka over millions of years.
Given such glories, it is not surprising that few tourists take note of the two concrete huts draped with black polythene that have been erected in a shadowy alcove in one obscure part of the 24km-long labyrinth. But the huts contain wonders of their own. In racks of trays of water, scientists have placed specimens of one of the world’s strangest creatures: the blind aquatic salamander Proteus anguinus – or olm, as it is known locally. It constitutes a project that could have profound implications for the future of these remarkable creatures.
“We now have 21 baby olms flourishing in our trays,” said Primoz Gnezda, a biologist working in Postojna Cave. “For the first time we have witnessed the hatching of proteus larvae – and, after one year, they are all healthy. And that gives us hope we can save our olms for the future.”
Olms spend their lives in total darkness in the Postojna cavern complex. They can grow to up to a foot in length, making them the world’s largest cave-dwelling animals and they can live up to a century, though they usually breed only once every six or seven years. The creatures can detect the bioelectric fields of other organisms – helping them hunt in the dark for their main prey, the cave shrimp. And experiments have suggested that they use the Earth’s magnetic field to orient themselves. In addition, they possess photosensitive skin: if you shine a torch on the tail of an olm, it will swim away from you.
That extraordinary set of attributes has brought olms considerable renown among animal lovers, not least David Attenborough who has included them in his list of endangered animals he would most like to save from extinction. They are, he says, “one of the ultimate specialists” in the natural world. They have adapted to living in total darkness by losing their sight and can survive for up to 10 years without food. “The olm lives life in the slow lane which seems to be its secret for living a long life… and perhaps that is a lesson for us all,” says Attenborough.
Given their remote, stygian home, it might be expected that olms would be relatively new to the world of science but their existence has been known about for centuries. That’s because their habitat – the subterranean pools and rivers of the great karst outcrops of Slovenia and the north Adriatic coast – occasionally becomes flooded during rainstorms and when that happens the olms get flushed out into the open. In medieval times, the appearance of these writhing, white, eyeless creatures in the midst of severe storms caused some alarm. Locals believed they were the spawn of a mythical beast, most likely a dragon. So they become known as baby dragons – and the name has stuck, not least on the mugs and fridge magnets on sale in the tourist shops. In fact, with their clammy white skin and tiny legs, olms look more like miniature versions of Gollum than baby Smaug.
Slovenia is extremely proud of its remarkable little blind salamander which featured on the country’s pre-Euro coins. But the creature faces problems. For a start there is the threat of pollution to its waters from surrounding factories and towns – many of which are outside Slovenia. It has also suffered from the attentions of collectors. As a result Proteus anguinus is now rated as vulnerable by the International Union for Nature Conservancy.
That explains the particular joy that met the news that young baby dragons had been bred and were now being carefully nurtured in that dark subterranean hut. It was the first time olms had been persuaded to breed in a scientifically controlled environment within Postojna Cave. “In the cave, in nature, olms hatch all the time,” said Saso Weldt, another cave biologist, “but nobody has ever seen that happen or seen a hatchling younger than about two years – until now.”
The discovery that a mother olm had started to lay eggs was made in January last year by cave guide Juan Pablo Maschio. He reported having seen one attached to the wall of the aquarium in the cave that allows tourists to see living examples of Postojna’s distinctive salamanders. Biologists who rushed to the tank found the mother fighting to fend off other olms. Three years earlier, in 2013, another captive olm had laid eggs but none hatched and many were eaten by the other olms in her tank. This time the Postojna team were able to move the other olms out of the tank and allow their “dragon mum” to go on to lay her eggs. On 30 May, four months after the first egg was laid, the first baby dragon was born. In the end, a total of 21 larvae were hatched. “It was just fantastic. We all had tears in our eyes,” said Katja Dolenc Batagelj, head of the Postojna Cave laboratory.
At present, all 21 baby dragons are thriving and have grown from 2 to 7cm over the past year, and studies of the creatures continue. Last year, Lilijana Mali, of the University of Ljubljana – working with Stanley Sessions of Hartwick College, New York, and others – discovered that olms have evolved a unique genetic feature in which a piece of Y-chromosome (in most creatures present only in males) has become attached to an X-chromosome. Such a translocation can mix up sex determination and cause gender ambiguity, even in humans. This translocation may have arisen to conserve genes that are useful in the olms’ lightless, low-food environments. However, it may also pose reproductive problems for the species.
“The establishment of our breeding colony in Postojna gives us a chance to carry out more research and see what has been the impact on the genes of Proteus anguinus in evolving in this strange environment,” says Mali.
The story underlines the importance of the Postojna team’s success in establishing a breeding colony. “There may be thousands of our baby dragons in the caves but equally there is a constant danger of pollution,” says Batagelj. “Only a slight change to the water here might have a devastating effect so this colony is a lifeline.”