We began this post as “The 10 Weirdest Salamanders and Newts,” but never got past what may be the weirdest salamander of them all: the Olm (Proteus anguinus), a blind amphibian native to the subterranean waters of caves of southern Europe. This animal is so strange and interesting, it deserves a post of its own. (The 10 Weirdest Salamander post will follow soon.)
The Olm lives in subterranean aquatic habitats within the Dinaric Alps in the countries of Bosnia and Herzegovina, Italy, Slovenia, and Croatia. It is the the only European species of the family Proteidae, an ancient family of salamanders, and is Europe’s only cave-adapted vertebrate (animal with a backbone).
The Olm lives in complete darkness and is a great example of the evolutionary principle of “use it or lose it,” or more accurately, the principle of why waste energy on something if you never use it. When they are young, Olm have normal eye development. But as the animal matures, the eyes disappear under its skin because it doesn’t need them. Although the animal is blind, their eyes (even under skin) are sensitive to light.
The Olm’s other senses, particularly those of smell and hearing, are highly developed. It can sense sound waves in the water and vibrations on land. It may also use Earth’s magnetic field to orient itself, detecting electric fields in a way similar to sharks.
In another case of use it or lose it, the Olm has no pigmentation in its skin. Its yellowish-white or pink skin is never exposed to the sun, or light of any kind. But its skin is still able to produce melanin. When exposed the light, the animal will turn darker.
Unlike most amphibians that live a double life—in water and on land—the Olm is entirely aquatic. It swims by twisting its snake-like body like an eel, helped by its poorly developed legs.
The Olm doesn’t go through metamorphosis like most other amphibians. Instead it keeps the features of its larval stage, like external gills, which form two branched tufts at the back of its head. Because of its aquatic lifestyle, it also retains its tail fin and lacks eyelids. The Olm has only three fingers on its forelimbs and two toes on its hindlimbs.
The Olm feeds on small crabs, snails and sometimes insects. Food can sometimes be scarce in a cave, but that’s not a problem for the Olm. It can eat large amounts of food at once, and store the nutrients. When food is scarce, it becomes less active and its metabolism slows down. Controlled experiments have shown that an Olm can survive up to 10 years without food!
The Olm has a surprisingly long life for an amphibian. It has a maximum lifespan of over 100 years; the lifespan of an average adult is around 68.5 years.
According to the EDGE website, there are many threats to the Olm, several of which are similar to threats to other amphibians: water pollution, overdevelopment, illegal collection for the pet trade, hydroelectric damming schemes, and casual and uncontrolled dumping of domestic and industrial garbage, among many other threats.
In Slovenia, the Olm is considered to be a national treasure. In 1982, the Olm was placed on a list of rare and endangered species, which also prohibits the trade of the species. It is also somewhat protected in Croatia, and in Bosnia and Herzegovina
The Olm is listed on the IUCN Red List as vulnerable because of its fragmented and limited distribution and ever-decreasing population.
To learn more about the Olm, please visit the Evolutionarily Distinct and Globally Endangered (EDGE) website.