The underground world
Slovenia is a world-renowned country for karstic phenomena and especially caves. Even the scientific term “karst” is used worldwide to describe geological phenomena formed during the dissolution of limestone and dolomite rocks, “The Karst” being the name of the extensive limestone plateau stretching from western Slovenia, to northeast Italy and northwest Croatia. Although the Karst is full of surface phenomena like dolines, poljes, limestone pavements and so on, the greatest natural treasures are found underground. In Slovenia there are around 10,000 known karstic caves, with an average 100 new caves discovered every year. Most of them are found in western and central Slovenia. Some of the most famous and beautiful caves in Slovenia include Škocjanske jame (UNESCO site), Postojnska jama, Križna jama and Planinska jama.
The Slovenian Karst is also known as one of the most species-rich in terms of its underground fauna, hosting about 400-450 species of cave animals. The first cave animals in the world were described using specimens from Slovenian karstic caves. The caves at Postojna are also known as the cradle of speleobiology, a branch of biology concentrating on the study of life lived underground.
Slovenia’s and Europe’s most famous cave animal is the Olm Proteus anguinus, an aquatic salamander living in underground watercourses of the Dinaric mountains. Its distribution range includes southern Slovenia, northeast Italy, Croatia and Bosnia and Herzegovina. Being a troglobite, it is totally adapted to life in the dark, having no eyes and no skin pigmentation. It also retains external gills and other larval characteristics into adulthood (neoteny). In 1986 a dark-coloured subspecies of the Olm was discovered in southern Slovenia. It is known as the Black Olm Proteus anguinus parkelj, living in a very restricted area in Bela Krajina. The main features that separate it from the nominate Olm are its normally developed eyes and dark (almost black) skin pigmentation.
Slovenian caves are also famous for the presence of another interesting cave animal, the first described cave beetle in the world: Leptodirus hochenwartii. This tiny beetle was discovered in 1831 in the Postojna cave. It has a northwestern Dinaric distribution and found in Slovenia, the Trieste Karst and Croatia.
Among the many other Slovenian troglobites, capable of living only in caves, we will mention just a few of the more famous: Velkovrhia enigmatica (an endemic cave Hydrozoan of Slovenia), Titanethes albus (an isopod crustacean or "woodlouse"), Niphargus sp. (an amphipod crustacean), Alona sketi (a cladoceran crustacean), Neobisium spelaeum (a cave pseudoscorpion), Stalita taenaria (a cave spider) and Anophthalmus hitleri (an endemic cave beetle of Slovenia, named after Adolf Hitler!).
Olm Proteus anguinus (Photo: Slavko Polak)
Neobisium spelaeum (Photo: Slavko Polak)
Prospelaeobates vrezeci (Photo: Slavko Polak)
Some animals known as trogloxenes or "cave guests", live only at cave entrances and cannot live exclusively in caves. The most typical examples are the Common Cave Cricket Troglophilus cavicola, Neglected Cave Cricket Troglophilus neglectus and various harvestmen arachnids (Opiliones).
Among animals that use caves only during part of their life, for resting or hibernating are various species of bats. The most common include Greater Horseshoe Bat Rhinolophus ferrumequinum, Lesser Horseshoe Bat Rhinolophus hipposideros, Mediterranean Horseshoe Bat Rhinolopus euryale and Common Bentwing Bat Miniopterus schreibersii.