Proteus Vivarium

Two hundred species of fauna (including cave beetles, bats, hedgehogs, and the 'human fish') found in the cave are studied at the Proteus Vivarium, which is part of a speleobiological research station located in the cave. It is open to visitors and has a video introduction to underground zoology. A 45-minute tour then leads you into a small, darkened cave to peep at some of the shy creatures you've just learned about.

Proteus anguinus is one of the most mysterious creatures in the world. A kind of salamander, but related to no other amphibian, it is the largest known permanent cave-dwelling vertebrate. The blind little fellow lives hidden in the pitch black for up to a century and can go for years without food.

The chronicler Valvasor wrote about the fear and astonishment of local people when an immature 'dragon' was found in a karst spring near Vrhnika in the late 17th century, but he judged it to be 'an underground worm'. Several other reports about this four-legged 'human fish' (človeška ribica as it's called in Slovene) were made before a doctor in Vienna realised its uniqueness in 1768. In announcing its existence to the scientific world, he called it 'Proteus anguinus', after the protector of Poseidon's sea creatures in Greek mythology and the Latin word for 'snake'.

Proteus anguinus is 25cm to 30cm long and a bundle of contradictions. It has a long tail fin that it uses for swimming, but can also propel itself with its four legs (the front pair have three small 'fingers' and the back have two 'toes'). Although blind, with atrophied, almost invisible eyes, Proteus anguinus has an excellent sense of smell and is sensitive to weak electric fields in the water. It uses these to move around in the dark, locate prey and communicate. It breathes through frilly, bright-red gills at the base of its head when submerged, but also has rudimentary lungs for breathing when outside the water. The human-like skin has no pigmentation whatsoever, but looks pink in the light due to blood circulation.

The question that scientists have asked themselves for three centuries is: how do the beasties reproduce? Its reproduction has never been witnessed in a natural state, and they haven't been very cooperative in captivity. It is almost certain that they hatch their young from eggs and don't reach sexual maturity until the (almost human) age of 16 or 18.