Their realm stretches from Italy through Slovenia and Croatia to Bosnia-Herzegovina and Montenegro. They are among the largest cave dwellers in Europe – and among the most mysterious. Perfectly adapted to absolute darkness, they have radically slowed down their metabolism, can survive long periods of food scarcity, are astonishingly resistant to cancer and display impressive regenerative abilities.
They are classified as endangered on the IUCN Red List. Paradoxically, their vulnerability lies in what makes them so fascinating: extreme longevity with very late breeding success.
Almost everything we know about the reproduction of olms comes from artificially created populations. Eggs and larvae have hardly ever been observed in the wild. Even in human care, their reproductive cycle is extremely slow: complete development from egg to adult is only observed about once every 12 years – and even then, females lay only about twenty eggs on average.
For a species that is already rare and only found in a few specialised habitats, this is a precarious situation. Any disturbance can cost entire generations.
Ultrasound in the cave laboratory
To decipher this enigmatic reproductive biology, the Leibniz Institute for Zoo and Wildlife Research relies on high-frequency ultrasound examinations. The method was successfully tested on cave salamanders in 2017 and makes it possible to determine their health status (e.g. parasite infestation, skin infections), precisely record their ovarian cycle and plan breeding measures that respect the animals' natural rhythm.
The breakthrough came in August 2018, when the IZW took over scientific supervision of the cave salamanders in Hermann's Cave in the Harz Mountains. The animals were brought to the artificially created cave system there in 1932 and 1956 – a unique refuge that has served as home to the salamanders for eight decades.
The dramatic challenge: cannibalism
As fascinating as olms are, breeding their offspring is a delicate matter. In recent years, eggs have repeatedly been discovered only to disappear again before they could develop into larvae. The suspicion: cannibalism – the animals are decimating their own next generation. No larvae have ever been observed, even though researchers discovered fertilised eggs in the bodies of female olms in early 2025. A great success, but one that nevertheless failed to produce offspring.
The solution: a second rearing system specifically for fertilised eggs and sensitive larvae. The requirements are extreme: constant temperatures below twelve degrees Celsius, protection from bright light, living miniaturised food and the highest water quality over many months. This requires sophisticated monitoring over years – with special night vision camera surveillance to track development processes without disturbing them.
Why olms are so valuable to science: How do they manage to live for over a hundred years without developing typical age-related diseases? Why are they so resistant to cancer? How does their regeneration work? These questions make olms key to medicine, ageing research and environmental science.
Why we support this project
The cave salamander project is significant for the Animal, Nature and Species Conservation Foundation for several reasons:
Protecting living fossils: By preserving the olm, we are not only protecting a unique species of amphibian, but also highly sensitive cave systems and a piece of Earth's history.
Scientific breakthrough: Their longevity, resistance to cancer and regenerative abilities provide valuable insights for medicine and environmental science.
Extreme vulnerability: Late reproduction, few eggs, infrequent reproduction – if one generation is lost, the consequences are dramatic.
Strong partnerships: Together with Dr Anne Ipsen, the Leibniz-IZW and local authorities, we combine basic research with practical species conservation.
What is happening now
Together with cave explorer Dr Anne Ipsen, local authorities and the foundation, a comprehensive programme is being developed to ensure the long-term survival of the olm. The programme focuses on a specialised system for keeping and breeding eggs and larvae, years of monitoring using ultrasound and X-rays, and comparing populations in human care with natural populations.
It is about development periods, embryonic development and sustainable breeding programmes that respect this extremely slow way of life.
Time for miracles
The goal is clear: these mysterious cave dwellers should still be gliding through their underground labyrinths in a hundred years' time – as living witnesses to a time when the Earth looked very different. While we live in a fast-paced world on the surface, the olms remind us that some wonders take time – a lot of time. And that is exactly what we want to give them.
Source: Prof. Dr. Thomas Hildebrandt, Dr. Susanne Holtze, Leibniz-Institut für Zoo- and Wildlife Research Berlin, www.izw-berlin.de