How does an olm get by in a cave with so little to eat?

In a limestone cave in eastern Bosnia and Herzegovina, biologists marked 26 olms and went back to look for them over eight years. Science News reports that most of the animals did not seem to move more than 10 meters (about 33 feet) from their original spots, and one appeared to stay in roughly the same place for seven years. Science News calls these low-energy animals, and in a cave with very little food, saving energy is a sensible business plan.

The olm (Proteus anguinus) is a pale salamander that keeps its gills for life and lives in underground lakes and streams of the Dinaric Alps. Its eyes are tiny and covered by skin. It eats rarely, moves little, and according to a captive colony in France it may live for a century. It is, by any measure, an unhurried animal.

This article follows the olm’s low-energy way of life: how it senses a world without light, what lab studies say about its long fasts, how slowly it grows up, and why a 2026 study suggests that “the olm” may be nine species. We flag every number that rests on a single source.

Meet the olm

The Animal Diversity Web (ADW), a University of Michigan database, says the olm is native to countries along the Adriatic Sea, from northern Slovenia and northern Italy south through Croatia and Bosnia and Herzegovina. Whether it reaches Montenegro and Serbia is uncertain. It lives in underground freshwater, usually deep in cave systems, often more than 300 meters (about 1,000 feet) below the surface, in water of 5 to 15 degrees Celsius. The Slovenian government’s science page calls it the only vertebrate in Europe that lives entirely in caves, and adds that after heavy rain some animals wash out into surface streams.

Living without light: eyes, skin and other senses

The ADW says the olm’s eyes are very small and do not break through the skin, though they keep some light sensitivity. The Slovenian page agrees that the eyes are atrophied, meaning shrunken, and covered with skin, but says the animal can sense light throughout its body. The sources do not explain why the eyes shrank. An obvious guess is that eyes are not much use in the dark, but that is a guess.

What replaces sight? The ADW lists highly sensitive chemoreceptors that detect very low concentrations of organic material in the water, which the olm uses to find prey. It has working ears that pick up sound from water and ground, plus a lateral line, a row of sensors that feels low-frequency water movement. It also has ampullary organs that detect electric fields. Their main function is unknown, and the ADW says they are thought to help locate prey. In all, the ADW says the olm uses a combination of chemoreceptors, electroreceptors and mechanoreceptors to locate and capture prey. Behavioral studies hint that the olm can orient to magnetic fields, according to the same account.

The menu is modest. The ADW lists small invertebrates such as cave crustaceans of the genus Niphargus, tiny snails and insect larvae. Science News describes crustaceans and snails as the olm’s sparse food in the caves.

A slow-motion budget: energy and long fasts

The strongest lab evidence comes from a 2001 study by Frédéric Hervant, Jacques Mathieu and Jacques Durand in the Journal of Experimental Biology. They compared the olm with a surface-dwelling Pyrenean newt during long-term starvation and refeeding. The newt lost its energy reserves steadily from the start. The olm did something different: it burned carbohydrate first, then fat, then a mix of fat and protein, and it kept sparing protein while entering an extended state of temporary torpor, a near-sleep in which the body slows down. The authors describe a remarkable resistance to long-term fasting and a very quick recovery from nutritional stress. The abstract we read does not say how long the fast lasted.

A second paper by the same authors, in Natura Croatica, adds that the olm had lower metabolic and activity rates than most surface amphibians and showed no apparent daily rhythm, unlike the surface species. The authors read this as an adaptation to cave life, where food is scarce and irregular and oxygen may sometimes be low.

What about the famous number? Science News says olms can go 10 years without eating. It offers no separate source, and the only basis it gives is that prey is scarce. We could not trace the figure to a measured experiment, so treat it as a popular claim. The lab work supports very long fasts, not a specific count of years.

A very long life, and very slow breeding

In 2010 a team led by Yann Voituron published an analysis of a captive colony in a cave at Moulis, near Saint-Girons, France. The cave was fitted with riverbed-like basins in 1952, and the paper says more than 400 animals of various ages live there. Breeding and deaths have been recorded weekly since 1958. The oldest animal observed was at least 48 years old, and probably around 58, since some were collected as young animals of unknown age.

From those records the authors predicted a maximum lifespan of about 102 years and an adult average of 68.5 years. Females mature at an average of 15.6 years and reproduce about once every 12.5 years. The ADW gives similar figures: maturity at 14 to 15 years and breeding about every 12 years. A female that waits until about 15 to breed, and then waits another dozen years, is not in a hurry.

Two cautions apply. These are predictions from a captive colony, and the authors note that the colony is fed more regularly than wild olms probably are. The ADW says the wild lifespan is poorly known. The Slovenian page also calls egg-laying a rare occurrence and says 22 growing young olms, affectionately called little dragons, were on show at Postojna Cave. The same page says the olm can regrow an amputated limb, the skill the axolotl is famous for.

What this looks like in practice: a cave census

Here is the Bosnian study as a worked example, as Science News reports it.

The study tracked positions, not energy use. Science News links the slow pace to saving energy, and the idea fits the lab findings above, but it is an interpretation, not a measurement.

Common mistakes and myths about the olm

Myth: blind means it senses nothing. The olm uses smell, vibration, hearing, an electric-field sense of uncertain purpose and light detection through the body. Only imaging vision is mostly gone.

Mix-up: it is a fish. A 2010 paper in Biology Letters uses the nickname “human fish” in its title, but the olm is a salamander. It lays eggs, as the ADW notes, and keeps its gills for life. The mudpuppy is another salamander that does the same.

Myth: it can go ten years without food, full stop. See above: one popular source, no traced measurement.

Mix-up: the olm is one species. The IUCN and GBIF treat it as one, but a 2026 study discussed below argues for nine.

Conservation status

The olm is listed as Vulnerable on the IUCN Red List of Threatened Species. That is the category as distributed by GBIF, the Global Biodiversity Information Facility, and we checked it on November 9, 2026. Vulnerable means the species was evaluated and faces a high risk of extinction in the wild.

The ADW names habitat destruction, water pollution, land changes from development and tourism, and illegal capture for the pet trade. It also says most olms live in national parks and protected land in Italy, Croatia and Slovenia. None of our sources states a confirmed population trend.

The picture may be about to change. The Societas Europaea Herpetologica reports a study, listed as in press, led by Christophe Dufresnes and colleagues in Amphibia-Reptilia. It recognizes nine species of Proteus, three newly described. The authors applied Red List criteria and say all nine are threatened, two with immediate danger of extinction, and that two live in a single groundwater system where one pollution event could wipe them out. We do not know whether or when the IUCN will reassess.

Categories are reviewed and can change, and the copy GBIF distributes can trail the IUCN website by some months, which is why we print the date we checked. GBIF’s copy does not give the year of the assessment, so we do not state one.