About the olm

The olm, Proteus or Proteus anguinus is an endemic species of subterranean fresh water habitats of the Dinaric karst. It is the only true subterranean vertebrate. It is distributed in Slovenia, Trieste in Italy, Croatia and Bosnia and Herzegovina. It was first described in 1768, while in Croatia it was first recorded in 1840 at the Goručica spring near Sinj. In the areas of Lika and Velebit the olm was never found. The exact reason why they were not found in that area is unknown, but it is assumed that this could be clarified with hydrogeological research.


Research has proven that there are two olm subspecies - white, troglomorphic * subspecies Proteus anguinus anguinus and dark-colored, nontroglomorphic Proteus anguinus parkelj. Representatives of the dark colored olm were found only in two springs in the Bela Krajina area in southeastern Slovenia, west of Žumberak.

The olm individuals retain larvae morphological characteristics in their adult stage. Their skin is pale, pink-white color, the skull is narrow and elongated, and on its head are small, stunted eyes covered with a layer of skin. One pair of red gills are located on its neck that they  retain throughout their life,  and have short limbs with only two fingers on its hind limbs and three fingers in the front. The total body length is up to 40.6 cm. They have a slow life development, and individual adult stage is achieved after 14-18 years. The olm is an amphibian with the longest life span, reaching up to more than 60 years. It breathes using gills and through skin, and in hypoxic conditions, it breaths using  lungs. It does not need high concentration of oxygen which is linked to their low metabolic rate, which is one of the adaptations to a subterranean lifestyle. It can sense very low concentrations of organic compounds in water. It uses scent to estimate the quantity and quality of prey.

*Troglomorphy is every morphological and physiological change or changes in animal behaviour as a result of adaptation to a subterranean lifestyle.


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