When humans in the 15th century encountered olms—rare amphibians that have been roaming Earth's caves for 200 million years—they thought they were baby dragons. Today we know little more about the blind creatures than our ancestors did. Olms inhabit the cave rivers of the Balkans, grow up to a foot long, can live for a century, and only need to eat once a decade, report the BBC and Slate. They also lay eggs about as often, which is why the 50 to 60 olm eggs stuck to the underside of a rock in Slovenia's Postojna Cave are so remarkable. The cave hosts a wild olm population alongside an aquarium visited by a million tourists each year. On Jan. 30, a female olm chose an area in the aquarium to lay her eggs, three of which are showing promising signs of growth, biologist Saso Weldt says. It will likely take at least four months for the eggs to hatch.
That is an uncertain estimate, he explained, based on a colony of olms that was established in the 1950s in an underground lab in the French Pyrenees. There, they live in slightly warmer water, at 11C.
"In our cave, it is slightly cooler, 9C, so everything will be prolonged."
It is a unique opportunity to observe the enigmatic olm - also known as the proteus - reproducing in the same caves where it has lived for millions of years.
"It is very significant because there is not a lot of data about anything, [relating to] the reproduction of this group of animals," commented Dusan Jelic, a Zoological Society of London Edge Fellow who studies wild olms by diving underwater through cave systems in Croatia.
If the baby olms hatch and develop healthily, Dr Jelic said, it would be "something amazing".
"In the wild, we never find eggs or larvae. They are probably hidden within some very specific localities within the cave systems."
There is just such a labyrinthine cave system in Postojna, with its own population of wild olms - but remarkably, this particular clutch of eggs has been laid in an aquarium in the cave's heavily trafficked visitor area.
"This is very cool - it is quite extraordinary," said Primoz Gnezda, another biologist working at Postojna Cave. "But also, we are quite scared that something will go wrong, because the eggs are very sensitive."
An infrared camera feeds live video to a nearby screen so that the cave staff, as well as tourists, can see what happens.
There is almost no movement, but occasionally the female olm stirs to check the eggs, to lay another, or to fend off amphipods - small, hungry crustaceans which she cannot see, but detects using electro-sensitive organs in her snout.
The animal also has a powerful sense of smell, which helps monitor the eggs.
"The eggs have a smell, so she can recognise which are alive and which are dead," explained Mr Weldt. "And because food is so scarce in the cave system, she eats the ones that are not fertilised."
The proteus is something of an icon in Slovenia, even appearing on coins before the arrival of the euro. Hundreds of years ago, when floods occasionally washed the creatures from the region's caves, they were regarded suspiciously as baby dragons.
In the last few weeks, the Postojna "dragon mum" has become quite a celebrity and carries a weight of expectation on her slimy shoulders.
That is an uncertain estimate, he explained, based on a colony of olms that was established in the 1950s in an underground lab in the French Pyrenees. There, they live in slightly warmer water, at 11C.
"In our cave, it is slightly cooler, 9C, so everything will be prolonged."
It is a unique opportunity to observe the enigmatic olm - also known as the proteus - reproducing in the same caves where it has lived for millions of years.
"It is very significant because there is not a lot of data about anything, [relating to] the reproduction of this group of animals," commented Dusan Jelic, a Zoological Society of London Edge Fellow who studies wild olms by diving underwater through cave systems in Croatia.
If the baby olms hatch and develop healthily, Dr Jelic said, it would be "something amazing".
"In the wild, we never find eggs or larvae. They are probably hidden within some very specific localities within the cave systems."
There is just such a labyrinthine cave system in Postojna, with its own population of wild olms - but remarkably, this particular clutch of eggs has been laid in an aquarium in the cave's heavily trafficked visitor area.
"This is very cool - it is quite extraordinary," said Primoz Gnezda, another biologist working at Postojna Cave. "But also, we are quite scared that something will go wrong, because the eggs are very sensitive."
An infrared camera feeds live video to a nearby screen so that the cave staff, as well as tourists, can see what happens.
There is almost no movement, but occasionally the female olm stirs to check the eggs, to lay another, or to fend off amphipods - small, hungry crustaceans which she cannot see, but detects using electro-sensitive organs in her snout.
The animal also has a powerful sense of smell, which helps monitor the eggs.
"The eggs have a smell, so she can recognise which are alive and which are dead," explained Mr Weldt. "And because food is so scarce in the cave system, she eats the ones that are not fertilised."
The proteus is something of an icon in Slovenia, even appearing on coins before the arrival of the euro. Hundreds of years ago, when floods occasionally washed the creatures from the region's caves, they were regarded suspiciously as baby dragons.
In the last few weeks, the Postojna "dragon mum" has become quite a celebrity and carries a weight of expectation on her slimy shoulders.