A particularly lazy cave salamander would have stayed in the same spot for 7 years

The eel proteus ( Proteus anguinus ), olm, or “cave salamander”, is a salamander known to be able to live in a very restricted area for years, without ever moving. Recently, researchers discovered an extreme case: a specimen remained in the same place for 7 years without ever venturing outside of its small “comfort” zone.

"They hang around, they do almost nothing," says Gergely Balázs, of Eötvös Loránd University in Budapest, Hungary. Olms are salamanders that live in European caves, known for their particularly slow lifestyle. They have adapted to living in total darkness: their skin is pale and their eyes do not develop, which makes them blind. Their life expectancy can reach decades, even centuries.

Their particular way of life makes them difficult to study in nature, explains Balázs, so that most of the observations are made on captive specimens.

One of the first long-term studies on wild olms

In an attempt to elucidate certain behavioral aspects of the animal, Balázs and his team carried out one of the first long-term studies on wild olms.

The researchers followed the olms living in the Vruljak 1 cave in Bosnia and Herzegovina. Between 2010 and 2018, the team entered the cave several times and marked the salamanders by injecting a unique, black pigment in their caudal fins. When they returned (regular and often spaced several months apart), they tried to find out where the marked olms were. A total of 19 specimens were tracked.

Most of them have moved less than 10 meters, although they have been recaptured years after being tagged. Most salamanders only moved an average of 5 meters per year! The most active olm had moved 38 meters in 230 days. On the other hand, another was found in exactly the same place after 2,569 days, more than seven years. The results of the study are available in the journal Journal of Zoology.

However, olms may be more active than the data suggests, says Gábor Herczeg, a colleague at Balázs. " We don't know the daily activity of these animals, " he says, noting that visits to the cave were often spaced several months apart. Olms can move in a tight space, he adds.

However, an inactive lifestyle would make sense to them. In fact, they are predators who use a “waiting strategy”, explains Balázs. Their prey is small crustaceans, which are not common. To save energy, the olm can sit still and slow down its metabolism until one of them approaches. "They can survive without food for years," he says.

Although the very slow lifestyle of olms is suitable for their underground habitat, it also makes them vulnerable to dramatic changes in their environment. If the conditions in their cave become inhospitable, for example due to the increase in floods due to climate change, they may find it difficult to move to a new habitat.


Extreme site fidelity of the olm (Proteus anguinus) revealed by a long‐term capture–mark–recapture study

G. Balázs  B. Lewarne  G. Herczeg

First published:28 January 2020


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