The Olm is the member of the group Tailed amphibian (Caudata). It is the endemic inhabitant of the underground waters of Dinaric areas of Slovenia, the Trieste area of Italy, Croatia, Bosnia and Herzegovina, and it is the only real underground vertebrate in Europe. Contrary to the most of other amphibian species the Olm never finishes the full metamorphosis (neoteny), but preserves some characteristics of the leach stage during the whole life (i.e. outer gills). It has snake-like body with four completely developed legs (only three fingers on the front and two on the hind legs). Adults can grow up to 25 cm, very rarely up to 35 cm. It spend entire life underground, so it does not have skin pigmentation and it is blind (except very young animals which have eye spots). Because of the white skin it got its Croatian name “human fish”. The only exception is the Black olm from Bela krajina in Slovenia.

The Olm can live very long, even 100 years, and becomes mature when it reaches ca. 14 years. Female usually lay eggs under stones in the water. Several times giving birth to live juveniles was recorded.

The first written note about the Olm dates from 1689. Valvasor wrote in his book “Slava vojvodine Kranjske”about it as the baby dragon. It was scientifically described, also based on the specimens from Sovenia, only in 1768 by the Laurenti. Seventy-two years had passed from this scientific description of Olm, until it was found in Croatian karst. The first specimen of the Olm in Croatia was found in 1840 at the Gorucica spring near Sinj.

After this first finding, the data about the Olm started to came from other localities all around the karst regions of Croatia. Today there are near 60 known finding places in Croatia.

Eduard Kletecki