A Cave-Dwelling Salamander Didn’t Move for Seven Years

The blind, eel-like amphibians called olms live deep in European caves and can go years without food

Olms, also called "baby dragons" and "human fish," are blind, foot-long salamanders native to European caves. Photo by Javier Ábalos via Flickr under CC BY-SA 2.0

Following stories of dragons, naturalist Janez Vajkard Valvasor traveled to Vrhnika, a town now in Slovenia, in 1689. After heavy rainfall, animals resembling baby dragons were swept out of nearby caves; could this be evidence that a mama dragon was lurking inside, perhaps? Not quite. Those baby dragons were actually olm salamanders, which max out at about 12 inches long and live to be 100 years old.

Olms are a bit magical though. Lacking both pigmentation and eyesight, they are super-sensitive the feeling of light on their skin. Even more fascinating, they can sense both electric and magnetic fields. They are also pretty lazy.
According to new research published in the
Journal of Zoology, one olm spent seven years without leaving its favorite spot.

“They are really good swimmers,” Eötvös Loránd University zoologist Gergely Balázs tells Science News’ Jake Buehler. Olms could “move around and try different spots to see if the neighbor is nicer, or there’s more prey… And they just don’t do it.”

Balázs and his colleagues began studying olms in the caves of eastern Bosnia-Herzegovina more than ten years ago. After several dives, the researchers began to suspect that some olms hadn’t budged. In 2010, the researchers labeled seven olms, and in 2016 tagged an additional 19. Each time they recaptured an olm, they tracked how far it had moved since the last time they saw it.

Out of 37 recaptures over the full study, only three olms moved further than 65 feet, and one olm was found in the same spot for 2,569 days, or just over seven years.

Olms live in cave systems without much food, and they can go for months or years without eating, writes the Independent’s Harry Cockburn. The animals also aren’t particularly sociable—they only mate about once every 12 years—and have no predators. The crustaceans and snails that olms snack on are both scarce and evenly distributed in their caves. It appears that if olms won’t benefit from moving, they just don’t, as Matthew Niemiller, a cave biologist at the University of Alabama in Huntsville who wasn’t involved in the study, tells Science News.

“If you’re a salamander trying to survive in this…food-poor environment and you find a nice area to establish a home or territory, why would you leave?” Niemiller says.

Other than a 2017 study that found DNA evidence of olms in caves where they hadn’t been seen before, research on these amphibious baby dragons has been completed in laboratory settings. In 2016, the first olm eggs were laid in captivity at Postojnska Caves, which gave researchers an opportunity to observe how they mature.

Most amphibians lose their external gills as they grow up, but olms never fully leave their larval state. In the latest study, Balázs and his colleagues estimated whether the animals were mature based on their size. Olms seven inches long were deemed adults. Olm larvae are susceptible to infection, so many die young, but olms that reach adulthood can live for more than a century.

Olms are listed as vulnerable species because they have a small, specific habitat range that’s broken up over many cave systems. They’ve caught the attention of naturalists from Charles Darwin, who called them “wrecks of ancient life,” to David Attenborough, who included them in his list of ten species he would most like to save from extinction.

“The olm lives life in the slow lane,” Attenborough says, per the Guardian’s Robin McKie, “which seems to be its secret for living a long life… and perhaps that is a lesson for us all.”

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