It’s been called everything from ‘dragon’s offspring’ to ‘the human fish’. The olm (aka Proteus anguinus) is the world’s largest cave-dwelling animal, and Europe’s only cave adapted vertebrate. It has a pale salamander-like body around 25cm long, and lives entirely within underground aquatic systems beneath the Dinaric Alps, spanning countries such as Slovenia, Croatia, and Bosnia and Herzegovina. Its subterranean existence means it is entirely sightless, instead utilising a powerful sensory system of smell, taste, hearing and electrosensitivity to find small crabs, worms, or snails to eat. Nevertheless, even if a meal is hard to come by, they can live for up to ten years without eating.
New images from the Pivka River flowing within the Postojna Cave, Slovenia, where an estimated 4,000 olms live and are studied, now provide a glimpse into the animal’s unique reproductive process. ‘Because they live most of their lives hidden away in subterranean aquatic habitats, we know very little about the reproductive biology of olms,’ says Liljana Bizjak-Mali, from the Biotechnical Faculty of the University of Ljubljana.
Photographs, such as the one displayed here, show an olm egg, the completion of a breeding cycle which can take as long as six or seven years to reach fruition. ‘Olms lay eggs, and these white, jelly-coated pearls are then fertilised one by one as the female attaches them to the underwater rocks deep in the caves,’ explains Bizjak-Mali. ‘Some had believed that Proteus sometimes deliver their young alive, like mammals, but we now know this is not true.’
“They are among the world’s most unusual species, ancient creatures from another world”
Olms are extremely popular in Slovenia, where in the past they have even made their way onto a national coin. However, even though it is forbidden to catch one without consent by Slovene authorities, there have been reports of olms being illegally collected and sold as pets.
‘They are among the world’s most unusual species, ancient creatures from another world,’ says Helen Meredith, from the IUCN SSC Amphibian Specialist Group. ‘Olms can survive hundreds of metres below the Earth’s surface in huge cave systems, yet their conservation is intrinsically linked to the management of land and rivers above ground.’
Tragically, even this isolated creature is suffering from population decline, as its fragmented distribution, loss of quality habitat, and increasing water pollution has earned it ‘vulnerable’ status by the IUCN Red List of Threatened Species. ‘Conserving forests and other native vegetation above cave systems, minimising the pollution of waterways, and not dumping refuse in cave entrances would all help protect this fascinating salamander,’ explains Meredith.
This was published in the March 2016 edition of Geographical magazine.