Olm Fact File
The olm is a salamander which spends most of its entire life in the dark of a cave. They have lost all color in their body and are covered by smooth white skin across the entire body except for the gills. These are feathery and placed on either side of the head They have thin walls meaning the red blood can be seen inside.
There are two pairs of legs with the front feet featuring three toes while the rear pair only has two. Their eyes are rudimentary and covered with skin but are still sensitive to light.
At the end of the body is a flat tail with a thin fin.
Their body measures between 20 and 30cm (8-12in) long. An average weight is up to 150g (5.3oz).
Olms are carnviores. Their diet is made up of small invertebrates and detritus. They can survive for up to 10 years without food.
Wild 8-9 years
— AD —
The species can naturally be found in Bosnia and Herzegovina, Croatia, Italy and Slovenia.
One of the populations in Italy was introduced during the 1800s. An introduced population also occurs in France where they were introduced to a cave of the subterranean laboratory of the CNRS France.
Large amounts of anecdotal evidence exist of a population in Montenegro but they are yet to be officially recorded here.
Their entire life is spent in the water within a limestone cave. The water temperature in their habitat is typically between 5 and 15°C.
In most cases the female will deposit up to 70 eggs on the underside of a rock. In some cases though the eggs are not laid and instead develop inside the body. The mother will then give birth to two fully formed young.
It is thought that temperature determines the breeding strategy to be used with colder temperatures prompting the use of the live birth strategy.
Sexual maturity is not reached until 12 years old. They also tend to only breed once every 10 or so years.
When threatened they will hide in crevices and sediment at the bottom of their cave.
They are unable to see and as such they use scent, touch and sound to find food.
Olms are considered incredibly lazy and rarely move far from a single spot. One olm in a study was recorded in the same spot for seven years before it moved.
When swimming they will move their body like a snake.
Unlike most amphibians even as adults they will breathe through gills. This is despite having fully functioning lungs.
Predators and Threats
Natural predators include fish and other amphibians.
The main threat posed by humans is through changes in habitat quality. Changes at the surface can affect the water quality in their caves.
They are reliant on access to clean water making pollution another major threat.
A small number of individuals are collected for the pet trade.
The olm is also known as a ‘baby dragon’ or ‘human fish.’
They were discovered during 1689 when heavy rains in Slovenia swept them out of their caves and to populated areas.
By Arne Hodalič – Author's own work. Uploaded with permission., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1923560
By Gzen92 – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=66783955
By Javier Ábalos Alvarez from Madrid, España – Olm (Proteus anguinus) in Moulis, Ariege (Laboratoire souterraine, CNRS), CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=58802184
Burnie, D., 2011. Animal. 3rd ed. London: DK
Martin, R., Bryan, K., Cooper, D. and Bond, S., n.d. The Animal Book. Lonely Planet.
Jan Willem Arntzen, Mathieu Denoël, Claude Miaud, Franco Andreone, Milan Vogrin, Paul Edgar, Jelka Crnobrnja Isailovic, Rastko Ajtic, Claudia Corti. 2009. Proteus anguinus. The IUCN Red List of Threatened Species 2009: e.T18377A8173419. https://dx.doi.org/10.2305/IUCN.UK.2009.RLTS.T18377A8173419.en. Downloaded on 22 December 2020.
EDGE of Existence. 2020. Olm | EDGE Of Existence. [online] Available at: <http://www.edgeofexistence.org/species/olm/> [Accessed 22 December 2020].
American Association for the Advancement of Science. 2020. Weird & Wonderful Creatures: The Olm. [online] Available at: <https://www.aaas.org/news/weird-wonderful-creatures-olm> [Accessed 22 December 2020].
Machemer, T., 2020. A Cave-Dwelling Salamander Didn't Move For Seven Years. [online] Smithsonian Magazine. Available at: <https://www.smithsonianmag.com/smart-news/cave-dwelling-salamander-didnt-move-7-years-180974233/> [Accessed 22 December 2020].
Softschools.com. 2020. Olm Facts. [online] Available at: <https://www.softschools.com/facts/animals/olm_facts/2712/> [Accessed 22 December 2020].