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Truly, olms have all the making of a vicious predator. In their cave habitats, they are at the top of the food chain. They are the largest cave-dwelling vertebrates in Europe, have exceptional hearing, devour their prey whole, enjoy eternal youth, live far longer than expected, and were once thought to be dragons.
But this curious salamander, found only in Slovenia, Croatia, and Bosnia and Herzegovina, is a small, pale creature, not very attractive and not very interesting. Its slow pace of living has given it the advantage of long life, but it suffers from neoteny – an inability to grow up. Even as an adult, olms display many of the same characteristics as a juvenile.
Locally, they’re known as ‘human fish’ because of their pale skin, although in the past they were thought to be baby dragons. They are, in fact, a troglodyte, and Europe’s only cave-adapted vertebrate. You may be disappointed to learn that at 25 centimetres, it’s also Europe’s largest cave animal. You won’t be needing any fancy weaponry around these guys. They look a bit like an eel, with teeny tiny legs poking out like toothpicks from their thick round bodies.
Olms are the most famous inhabitants of Postojna, a huge cave complex in Slovenia which is a popular tourist destination. You’re unlikely to find one if you visit – they prefer to stay in the dark, staying quite still, and not expending too much energy. They are almost entirely blind, and rely on electro-sensitivity and a well-developed sense of smell to detect their prey. They feed mostly on cave detritus, as well as small crabs and snails. When pickings are good they can gorge on a huge amount of food. Life in a cave is not without its hardships, and the olm has adapted to be able to slow its metabolic rate when food is scarce, even reabsorbing its own tissues. Scientists believe that it is possible for the olm to survive for up to ten years without food.
However, coming from such a small region means that the olm is considered a vulnerable species. It has adapted so acutely to life in the karst caves of the Dinaric Alps that any changes, no matter how slight, can affect it. The key dangers to olms are habitat loss and pollution. In Slovenia, it is considered a national treasure and legislation exists to protect olm habitats, but their numbers continue to decline.
Olm, the little dragon, lion of the deep, long may you continue to creep through the crystal clear waters of karst caves.