Specimen of the Week 303: the olm
By Will J Richard, on 4 August 2017
Hello! Will Richard here, finishing the week with another specimen. For this blog I’ve chosen an extraordinary little animal that you really can’t believe actually exists. But hey… that’s evolution. Readers… I give you the olm.
The olm (Proteus anguinus) is an aquatic salamander native to the caves of Central and Southern Europe. They live entirely in the dark so their eyes are rudimentary and hardly ever used. Instead olms are especially sensitive to smell, touch, movement and even electricity. This helps them to track prey by the tiny currents produced when muscles contract. They feed on a wide variety of detritus, small crustaceans and insects though, despite their sensitivity, food is scarce and difficult to find. To compensate olms can gorge themselves in times of plenty and then store fat and carbohydrates in their liver. When there is little or no food available they reduce their activity levels and live off these stores. Desperate olms have been shown to survive for a decade without eating.
Slow to grow
Most amphibians have a clear developmental cycle with a dramatic metamorphosis between the larval and the adult forms: think tadpoles and frogs. Olms, however, never really grow up. In an excellent example of neoteny, they retain a number of key larval characteristics, such as their gills and tails, throughout “adulthood”. They are also very slow to even develop so far as they do, taking as long as 15 years to reach sexual maturity and possibly living to more than 100.
One olm or two?
Most olms have translucent, pink bodies lacking pigmentation. The black olm (Proteus anguinus parkelj) however, as its name suggests, does not. The subspecies was found for the first time in 1986 and occurs only in a 100 square kilometre region in the southeast corner of Slovenia. Interestingly, this pigmented version prefers warmer, shallower water, has functional eyes and less sensitive other senses. It would appear to represent a half-way house between the ancestral nontroglomorphic (i.e. does not live in a cave) salamander and the more widely found white olm.
Although olms would seem to be protected from growing human populations by living in caves that are relatively untouched, this is not the case. Olms need clean water and are therefore highly susceptible to pollution. Changes in land use, expanding industry and agricultural run-off have a direct impact on the water systems which flow both above and below ground, destroying the viability of their habitat. They are also, by nature of their lifestyle, very difficult to survey… and we don’t even know how many species of olm we’re dealing with…
Will Richard is Visitor Services Assistant at the Grant Museum of Zoology.