Olm - Meet the Baby Dragons

In January 2016, a fairy tale became reality: the news that the eggs of dragon's offspring had been laid spread around the world.

Olms have been intriguing people for centuries, the news about them reaching even the far corners of the region back in the day. This was mainly owing to people's vivid imagination, the mystery surrounding the species and the polymath Johann Weikhard von Valvasor, who wrote about the dragon living in...

A rare gem

Due to the increasing pollution of subterranean waters and the human impact on the underground ecosystem the number of living olm specimens has been on a steady decline and olms were in 2009 also listed as an endangered species by The World Conservation Union. Sir David Attenborough, the legendary British naturalist and author of numerous BBC documentaries, picked olms as one of ten endangered animal species that he would take on his very own "Noah's Ark":

Olms are one of the greatest experts at adapting to their environment.

The anxious wait for the baby olms to be born is thus an extremely important event for Slovenia, the natural sciences and scientists worldwide.

Eagerly awaiting the baby dragons

On Saturday 30 January 2016, one of the Postojna Cave guides noticed that there was an olm egg attached to the glass wall of the aquarium in the Postojna Cave's Concert Hall. Next to the egg, there was a pregnant female olm guarding the egg. People around the world enthusiastically welcomed the first egg and are now eagerly waiting for the olm babies to hatch.

Olm diary

30. January


Cave guide Juan Pablo Maschio noticed the first olm egg and informed the management and the experts in charge of it. All other olms, which could disturb the egg-laying process, or even eat the eggs, have been removed from the aquarium, with only the dragon mum and her egg left in it.

Did you know?

The pregnant female olm is fiercely defending her eggs from the other olms.

03. February


A new egg has been spotted in the aquarium. In the last three days, the female olm relocated its egg-laying territory to the underside of a flat rock – one of the two ideal spots.

Did you know?

The olms mark their territory by means of chemical signals.

11. February

DAY 13

During the night, the olm has given us a few more reason to be happy – today, there were 24 eggs in total, arranged on both sides of the flat rock.

19. February

DAY 21

The female has laid egg number 52. The camera allowed us to watch cave amphipods (i.e. small crustaceans used in our aquarium to feed the olms) getting nearer to individual eggs. While the female was away, we could see three of them trying to bite through the egg envelope. As soon as the female returned, she immediately noticed them and attacked them.

Did you know?

Olms have a very well developed sense of smell and taste and are able to smell the food and also assess its quality by smelling. And more importantly, they are also able to detect even weak electric fields of other animals, which is most helpful in complete darkness.

24. February

DAY 26

We had a visit by an expert on the biology of olms, Dr Lilijana Bizjak Mali, from the Biotechnical Faculty in Ljubljana, and Dr Stanley Sessions, an expert on integrative biology of amphibians from Hartwick College, New York, USA. They examined the eggs and found that some of them were showing signs of development.

Did you know?

In the USA, Dr Sessions, among other things, researches the closest olms’ relative, i.e. a urodele amphibian from the genus Necturus. Necturi live in the surface waters of the eastern coast of North America. Ancestors and relatives of the olm hereabouts were also surface-dwelling animals. They died out during the ice age period.

08. March

DAY 39

Discovery Channel visited Postojna Cave to produce a feature about the one-of-a-kind event that is taking place in Postojna Cave.
The precious eggs have received extensive coverage by a number of media outlets across the globe. But the mystery remains hidden in the darkness, recorded only by means of an infrared camera.

15. March

DAY 46

We regularly check the water levels of the subterranean River Pivka, the olms' natural habitat. The river has risen. High water levels put olms in danger as the water may take olms outside of the cave, where most of them die.

Did you know?

In Slovenia, olms are a protected species under the animal protection act. Since 1982, olms have also been listed as a rare and endangered species.

28. March

DAY 59

The female suddenly left the eggs and moved to the other end of the aquarium, where she laid another egg. The biologists are speculating that this might have been olms' natural behaviour in order to give the eggs located in different spots a stronger chance of survival.

Did you know?

Interesting fact: According to the statistics, a mere two baby olms successfully hatch from 500 eggs in nature.

01. April

DAY 63

Some of the eggs are unfertilised. They can be recognised by the lack of development, which is slowly followed by the first signs of decay. The decaying eggs become muddy and this is when they need to be removed.

10. April

DAY 72

The olms were seen making S-shaped movements, which made for a proper little dance performance and a source of entertainment for the cave visitors who were watching it on the screen inside the cave.

27. April

DAY 89

The big relocation. The rock was carefully moved into the container used to move it to the aquarium, which had been set up some distance away from the main cave tour route. Some of the eggs fell off and were moved onto the mesh-like metal construction – some sort of an olm 'nursery'. Thus, their development now continues close to the surface, where there is plenty of oxygen.

Did you know?

Olms have a life expectancy of up to 100 years and can survive without food for up to 10 years.

07. May

DAY 99

The gills of our embryos are slowly branching. The blood circulation and the first heartbeat are noticeable. Life is becoming more and more tangible. The embryos have become considerably calmer.

Did you know?

Olms breathe with external gills, as well as with rudimentary lungs and the skin. They have an inner ear, which serves both the purposes of balance and hearing.

17. May

DAY 109

Our offspring is spontaneously lying on the back. We are about three periods of change away from the eggs hatching. Earlier today, we were happy to see an embryo turning around in the egg envelope rather vigorously for more than an hour. It won’t be long now until we get to see it.

Did you know?

Depending on the water temperature, the olms' embryo development inside an egg may takes up to 140 days, which is extremely long compared to other urodeles (i.e. amphibians that have a tail throughout life).

20. May

DAY 112

We received another visit by Dr Mali and Dr Sessions. Dr Mali took a photograph of an embryo under the microscope.
She made us happy by pointing out that a small dimple for the toes is already visible on the limb rudiment, which is a sign that it is not long until the hatching stage.
The embryo seems to be in the development stage 19 according to Briegleb.

The gills are more branched, the eye pigment is visible, the heart is beating and is supplied with blood. The size of the embryo is between 17 and 18 mm.

Did you know?

Did you know: olm larvae have eyes, which are in adult olms covered by a layer of skin.

30. May

DAY 124

On 30th of January 2016, one of the Postojna Cave guides noticed an egg attached to the glass of the aquarium in the Concert Hall. Located nearby was a pregnant female olm, protecting the egg. The global public enthusiastically welcomed the first egg and waited with baited breath for the hatching of baby dragons to begin. On the 30th of May, 124 days later, the first baby dragon hatched into the darkness of the underground world and the light of the world of excited fans.

01. June

DAY 125

Only one day after the first baby dragon, its younger sibling was caught in the act during hatching. Another moment of new life being born was captured.

14. June

DAY 138

Our firstborn is growing, the eyes and the feet are clearly visible. These days she is keeping busy swimming to the surface and back. Not long after, our brave olm was joined by 12 other newly hatched siblings.

15. June

DAY 139

Another olm hatchling has made its way out of the egg. If this makes you think ‘so what’s new’, think again. This particular hatchling is obviously being very cautious, knowing that it is not good to be reckless and hasty. Therefore, it started breaking through the egg envelope with its tail, and hatched differently than what happens usually, i.e. with its tail first and only then – after it had made sure everything was fine – the head followed as well. 

16. June

Day 140

The fast growing hatchlings will soon need to be moved into aquariums, each of them into its own, which is quite a delicate process. However, all of this makes for some 'pleasant problems ' for our biologists, who are busy preparing the first batch of food supplies for our baby dragons to feed on when they are ready to show the first teeth.

18. June

DAY 142

What do you call someone who survived even though most of the people had believed (s)he would not make it? Someone who, statistically speaking, was least likely to make it because his/her living conditions were simply too harsh. Someone who surprised and impressed all others with his/her birth, perseverance and persistence. The perfect name seems to be... Boris!

Boris hatched from an egg that was closest to the infected – mouldy – eggs, so we had to move him to a special container, which had no special filtration and the water was filtered in a ‘natural’ way. In the meantime, we waited and waited. And on day 142, Boris finally made it and posed in front of the camera somewhat cheekily. Welcome, Boris, you wild little thing, we wish you good luck. 

22. June

DAY 146

Up and down, up and down, the hatchlings are romping around their containers. They love swimming to the surface and back to the bottom of the container. It seems they get more than enough energy from egg yolk. With their heads, which are already trapezoid-like in shape, they increasingly resemble adults. But they are not yet white, they are still nicely pigmented. On the largest of hatchlings, hind legs are already visible as well.

25. June

DAY 149

As with any child, there comes a time for some measurements and numbers. When it comes to olm hatchlings, this needs to be done without touching, so a grid sized 1 x 1 cm has been placed at the bottom of the aquarium. The largest ‘dragons’, which hatched first, are now between 2 and 2.5 centimetres long. In some of the hatchlings, yolk is still visible in the abdominal area and some already have all three digits on their front feet.

29. June

DAY 153

While the hatchlings are still feeding on yolk, we are busy preparing food. Five embryos are still waiting in the egg envelopes. It has been more than a month since the first hatching and we expect the mouths of the oldest hatchlings to start developing soon, which means they will have to start eating. This is one of the most uncertain moments, which is making us increasingly nervous. 

07. July

DAY 161

Our two biologists once again rolled up their sleeves and made their way to one of the few perfectly clean parts of the River Pivka to get some mud, which they then put into a special Petri dish and placed it in the container with one of the olm hatchlings. We wanted to check how the hatchling would react to elements from the natural environment. The baby dragon was happy to plunge into the mud and also made good use of the Petri dish itself, hiding under it. As olms like being right next to stones because this makes them feel safe, we set up some hiding places made of glass for others as well, where they are now resting happily. 

14. July

day 168

Yoyo has hatched! The last baby dragon. We named it Yoyo, as it was – while still inside the egg – literally hanging from the stone on a string, moving back and forth. A day before, the so-called Laggard had finally hatched too. This hatchling had wanted to really make sure it was worth coming out of the egg envelope. We noticed that in terms of their size and development the last two hatchlings were very similar to others who had hatched well before them. It looks like they were overdue, having developed in the egg envelope in the same way they would have outside of it.

20. July

day 174

The baby dragons are hungry. Five days ago, we treated the four oldest and largest ones to a proper feast – some delicious worms. Two of the hatchlings were happy to eat them. Although almost all olm hatchlings still have some yolk reserves left, the fact that they are already eating means they are developing just the way they are supposed to. In the days after, we fed the worms to the other hatchlings as well and we are happy to report that some of them munched their way through the prey like fearsome dragons. 

28. July

day 182

Little toes, limbs and mysterious lines. Some of our baby dragons already have three toes on their forelimbs and their hind limbs are growing and developing quite nicely too. One of the baby dragons lifted its head for the first time earlier today, which is another good developmental sign. They are developing their predatory instinct. They are now able to sense worms (i.e. their lunch) from quite a distance; they slowly approach the worms and eat them quickly. Therefore, you'd better be careful. The baby dragons may be cute, but they can grab hold of you before you know it.

16. August

DAY 201

The baby dragons are losing weight – as far as development goes, this is perfectly normal, as our hatchlings are growing in length; in fact, some of them are now even more than three centimetres long. The legs of the most developed ones are already functional, i.e. the baby olms have ten digits, four legs and are busy exploring their surroundings as we speak. When hunting for worms they are making use of their rear legs – they are using them to move around. The most advanced baby olm explorers resemble the dragon momma more and more every day and are growing very fast. Dear baby dragons, you’re welcome to overtake in the left-hand lane, but do it with caution and with best of luck. 

07. September

Day 223

It’s been 110 days since the very first baby dragon hatched. According to a developmental stage table that was published by researcher Durand in 1963,  this period (110-120 days) completes the olms' larval stage and a juvenile or adolescent period starts. The baby olms are between 3.5 and 4 cm in size, their bodies are getting longer and the ratio between the thickness and the length is 1 to 12. Their legs are functional, the head is trapezoid in shape and flattened.  During the larval stage, the baby olms' growth was fast, while during the juvenile stage it slows down.


10. October

Day 256

Shuffle, shuffle, shuffle! 

This is the sound of our baby dragons carefully and slowly moving towards prey. Their hunting instinct is very much alive and kicking. Their eyes are clearly visible, the pigment is still present, but the yolk is all gone, as they now make sure they are not hungry themselves. The biggest baby dragons are between 4.5 and 5 cm long. As far as their looks are concerned, they are now already very much alike adult olms. 

22. November

Day 298

During the past few months, it may have seemed that everything revolves around our baby dragons, but we haven’t forgotten about our adult "dragons". But as far as they are concerned, everything runs smoothly and they are also much less demanding than the little "monsters". Their aquariums need to be cleaned and they have to be fed on a regular basis, and we need to have a bit of a talk with them from time to time when nobody is listening :). To make sure our adult olms get to enjoy a delicious feast, i.e. some amphipods, our two resident biologists need to get down to work, put on some boots, get into the water and catch some amphipods in the stream. Since no dangerous foreign bodies are allowed in the aquariums, the two biologists need to carefully pick the amphipods using a straw. It’s a hard job, but a fun one too. And in the late autumn, also a slightly cold one. 

01. December

Day 307

While our adult olms are feasting on fresh amphipods, the baby dragons enjoy spending time in their hidden kingdom. We are still seeing to their food, and making sure they have their favourite "furniture" at hand – rocks, which they can hide behind. All of the baby dragons are now 5 cm or more in length. May they be growing just as fast as they have so far.

31. December

day 337

A big dinner, some dancing, some fun and games until midnight and then the fireworks. This may sound like your New Year's Eve, but the baby dragons had an evening just like this. After seven months since the (first) hatching, our baby dragons are now up to six cm long, which means that – on average – they are three times bigger than when they hatched. They started the new year with luck on their side, and we hope it stays there. Happy New Year from the dragon's underground nest.

13. January

day 350

Two olm babies made sure there was a bit of a panic. We noticed the two oldest olm hatchlings had white spots on their heads. Without having a closer look at it, we were not sure what it was, so naturally we got worried something was wrong. Therefore, the whole team got together and made their way into the cave with a lump in their throat instead of going home to do some Friday afternoon 'couch potatoing’. Dr Mali and Dr Sessions made it from Ljubljana during a blizzard as well. "They are growing up," was our team's official diagnosis. The white dots obviously signify a loss of pigment, which we had said would happen. In about a year, "white spots" will cover their entire bodies and the hatchlings will change "colour" and thus become even more similar to their parents; in fact, during adolescence, pigmentation gradually decreases, until it has completely disappeared. Beautiful, but somewhat painful at the same time. They will grow into proper big dragons almost too quickly.

10. February

day 378

Over a year ago, on 30 January 2016, the daily work of the three-member Postojna Cave laboratory team changed completely and ever since then their workdays kick off in a totally different way. For more than a year now, the team leader and head of the underground laboratory, Katja Dolenc Batagelj, has been starting off her working day by observing the baby dragons in the laboratory, while our two resident biologists make sure the young olms get all the living food they need. Even now, more than a year later, the team members visit the laboratory every single day, keeping an eye on the development of 21 olm juveniles, providing them with the food (every three days), changing the water and making sure the olms have the optimum living conditions. According to experts, the Postojna Cave laboratory is a remarkable success that is setting new paradigms; in fact, owing to a high number of olm survivors it is currently considered the most successful cave laboratory in the world. Here's to a lot of success and luck in taking care of the baby dragons in the future! J

Hello, world!

day 367

The baby dragons are celebrating! It's been exactly one year since the first olm egg was found on the glass of the large exhibition aquarium. Our 21 baby dragons are now six centimetres in length. When they hatched, their front legs were fairly well developed with digit gaps, while their rear legs were underdeveloped with digit rudiments. Now, all of their four legs are developed with a total of ten digits. Their head, which was short at the time of hatching, now already resembles a duck's beak, their pigmentation is gradually disappearing, their eyes are still visible. When olms hatched, their mouths had no opening, but had teeth rudiments and yolk reserves. Now, the yolk is all gone, their predatory instinct is well developed and the baby dragons finish off their prey in no time without hesitating, which you see on the following link:  https://www.youtube.com/watch?v=GP0xltqovrA