The olm, or the white cave salamander (Proteus anguinus) is the only representative of the Proteidae family in Slovenia, and at the same time the only European vertebrate that permanently lives in caves. In surface watercourses that flow from the caves, we usually obtain them only after heavy rainfall, when the swollen waters carry away the olm that have not managed to retreat to safety in time.
In cross-section, the olm has a pale skin-coloured hue and continues into a relatively short tail, laterally flattened. From the beginning of the blunt snout to the end of the tail, the adult animal measures between 20 and 30 cm. Its body is distinctly elongated, the front and rear pair of small limbs is placed far apart. On the front feet it has three, on the hind ones only two digits. Behind the flat pear-shaped head, pink external gills are developed on both sides of the body. This respiratory organ is characteristic of amphibian larvae, but in the olm it is retained throughout life, although simple lungs also develop. The appearance of the animal maturing sexually, while it still looks like a larva, is called neoteny. After mating the female lays eggs about 1 cm in size, which she attaches individually to stones along the banks of underground stream beds. Sometimes, instead of eggs, the female lays some live larvae. This is a long-lived animal, which is believed to live up to 100 years.
It is a predator that, with snake-like writhing of its body, swims quickly and hunts cave-dwelling aquatic invertebrates, as well as crayfish or insect larvae that the surface water current brings into the cave, and none escape it.
Thus, the olm lives exclusively in underground waters and is well adapted to life in complete darkness. It senses its surroundings with the help of smell and via vibrations, which it detects with sensory organs distributed in the skin. Its eyes are reduced and covered with skin, as they are of no use in a lightless environment, but the entire surface of its body is sensitive to light.
It is an endemic of the Dinaric Karst, which means that its distribution area (areal) is limited to underground water bodies of the karst world of the Dinarides. Fran Erjavec, in his booklet Frogs, named it as one of the wonders of the land of Carniola, and this name is certainly deserved by the olm, as the only European cave vertebrate and, moreover, an endemic.
In Slovenia, the olm is protected and classified as a vulnerable species (VU) on the Red List! Moreover, the European Union has identified the olm as one of the Natura 2000 qualifying species, since by protecting its habitat within Natura 2000 special protection areas, together with the olm we also protect other inhabitants of the underground world and preserve its biodiversity for our descendants.
