Olms are aquatic salamanders found exclusively in European caves. Unlike most amphibians, olms live their entire lives underwater.
Olms are endemic to the waters flowing through limestone bedrock in the Dinaric Alps: a mountain range in southern and southeast Europe, stretching from northwest Italy along the Western Balkan Peninsula down to Albania.
Olms were first mentioned in 1689 by naturalist Johann Weikhard von Valvasor, who reported that, after heavy rains, olms washed up from underground waters. They were believed by locals to be the offspring of cave dragons.
Olms live in well-oxygenated, cold (8–11 °C), stable-temperature water.
Olms are well adapted to their watery domain. Blind, with undeveloped eyes, olms have keen hearing and sense of smell. Olms are known as “white salamanders” because their skin lacks pigment.
There is also a black olm, which is a subspecies with a shorter head and more developed eyes. Black olms are endemic to underground waters near Črnomelj, Slovenia.
A female olm lays up to 70 eggs, carefully placing them in rock crevices and protecting them until they after they hatch. Females breed every 12.5 years.
Olms exhibit neoteny: retaining features characteristic of early development in other salamanders. Neoteny is the retention of traits in adulthood of those only previously seen during development.
Olms live a sloth-like lifestyle. “They are hanging around, doing almost nothing,” reports Hungarian zoologist Gergely Balázs.
Olms patiently wait for prey – small crustaceans – to flow by. “They can survive without food for years,” says Balázs.
Olms may live for up to a century.
G. Balázs et al, “Extreme site fidelity of the olm (Proteus anguinus) revealed by a long-term capture-mark-recapture study,” Journal of Zoology (28 January 2020).
Michael Marshall, “A lazy cave salamander didn’t move from the same spot for 7 years,” New Scientist (2 February 2020).
Proteus anguinus (olm) photo courtesy of Boštjan Burger.