Editing Olm

{{Short description|Species of amphibian}}
{{Other uses}}{{Speciesbox
 | name = Olm
 | image = Proteus anguinus Postojnska Jama Slovenija.jpg
 | image_caption = Olms in [[Postojna Cave]], Slovenia
 | status = VU
 | status_system = IUCN3.1
 | status_ref = <ref name="IUCN">{{Cite iucn|author=IUCN SSC Amphibian Specialist Group |year= 2022 |title= ''Proteus anguinus'' |page= e.T18377A89698593 |doi=10.2305/IUCN.UK.2022-2.RLTS.T18377A89698593.en |access-date=6 August 2023}}</ref>
 | genus = Proteus
 | parent_authority = [[Josephus Nicolaus Laurenti|Laurenti]], 1768
 | species = anguinus
 | authority = [[Josephus Nicolaus Laurenti|Laurenti]], 1768
 | subdivision_ranks = Subspecies
 | subdivision = 
{{species list
|Proteus anguinus anguinus|[[Joseph Nicolai Laurenti|Laurenti]], 1768
|Proteus anguinus parkelj|[[Boris Sket|Sket]] & Arntzen, 1994
(See text)}}
 | range_map = Proteus anguinus distribution.png
 | range_map_caption = Native range (pictured: northeastern coast of [[Adriatic Sea]]).{{efn|Assuming contiguous inhabitance. According to newer assessments, the range is fragmented to smaller areas within the marked area.<ref name="IUCN"/>}}
}}

The '''olm''' ({{IPA|de|ɔlm|lang|De-Olm.ogg}}) or '''proteus''' ('''''Proteus anguinus''''') is an aquatic [[salamander]] which is the only [[species]] in the genus '''''Proteus''''' of the family [[Proteidae]]<ref name="AOTW">{{cite web |url= https://amphibiansoftheworld.amnh.org/Amphibia/Caudata/Proteidae/Proteus |title=''Proteus'' Laurenti, 1768 |last= Frost |first= Darrel R. |date=2023 |orig-date= 1998 |website= Amphibian Species of the World |publisher=[[American Museum of Natural History]]
|access-date= 19 March 2023}}</ref> and the only [[Troglobite|exclusively cave-dwelling]] [[chordate]] species found in Europe; the family's other extant genus is ''[[Necturus]]''. In contrast to most [[amphibian]]s, it is entirely [[aquatic animal|aquatic]], eating, sleeping, and breeding underwater. Living in caves found in the [[Dinaric Alps]], it is [[endemic]] to the waters that flow underground through the extensive limestone bedrock of the [[karst]] of [[Central Europe|Central]] and [[Southeastern Europe]] in the basin of the [[Soča]] River ({{langx|it|Isonzo}}) near [[Trieste]], [[Italy]], southern [[Slovenia]], southwestern [[Croatia]], and [[Bosnia and Herzegovina]].<ref name="Sket1997">{{Cite journal |last=Sket |first=Boris |date=1997 |title=Distribution of ''Proteus'' (Amphibia: Urodela: Proteidae) and its possible explanation |journal=Journal of Biogeography |volume=24 |issue=3 |pages=263–280 |doi=10.1046/j.1365-2699.1997.00103.x|bibcode=1997JBiog..24..263S |s2cid=84308933 }}</ref> [[Introduced species|Introduced]] populations are found near [[Vicenza]], Italy, and [[Kranj]], [[Slovenia]].<ref name="AW">{{Cite web |url=http://www.amphibiaweb.org/cgi-bin/amphib_query?where-genus=Proteus&where-species=anguinus |title=Proteus anguinus |last1=Bulog |first1=Boris |last2=van der Meijden |first2=Arie |date=26 December 1999 |website=AmphibiaWeb |access-date=27 January 2014}}</ref> It was first mentioned in 1689 by the local [[naturalist]] [[Johann Weikhard von Valvasor|Valvasor]] in his ''[[The Glory of the Duchy of Carniola|Glory of the Duchy of Carniola]]'', who reported that, after heavy rains, the olms were washed up from the underground waters and were believed by local people to be a cave [[dragon]]'s offspring.

This [[cave salamander]] is most notable for its adaptations to a life of complete darkness in its underground habitat. The olm's [[eye]]s are [[Vestigiality|undeveloped]], leaving it blind, while its other [[sense]]s, particularly those of [[olfaction|smell]] and [[hearing (sense)|hearing]], are acutely developed. Most populations also lack any [[biological pigment|pigmentation]] in their [[skin]]. The olm has three toes on its forelimbs, but only two toes on its hind feet. It exhibits [[neoteny]], retaining [[larva]]l characteristics like external [[gill]]s into adulthood,<ref name="animal">{{Cite book |title=Animal |date=2001 |publisher=DK |isbn=0-7894-7764-5 |editor-last=Burnie D. |location=London |pages=61, 435 |editor-last2=Wilson D.E.}}</ref> like some American amphibians, the [[axolotl]] and the mudpuppies (''Necturus'').

== Etymology ==
The word ''olm'' is a [[German language|German]] [[loanword]] that was incorporated into English in the late 19th century.<ref>{{Cite web |url=http://www.oxforddictionaries.com/definition/english/olm |archive-url=https://web.archive.org/web/20130315134559/http://oxforddictionaries.com/definition/english/olm |url-status=dead |archive-date=March 15, 2013 |title=olm |website=Oxford Dictionaries |access-date=2015-12-09}}</ref> The origin of the German {{lang|de|Olm}} or {{lang|de|Grottenolm}} 'cave olm', is unclear.<ref name="Seebold">{{citation |last=Seebold |first=Elmar |author-link=Elmar Seebold |year=1999 |title=Kluge Etymologisches Wörterbuch der deutschen Sprache |trans-title=Kluge's Etymological Dictionary of the German Language |language=de |edition=23rd |location=Berlin |publisher=[[Walter de Gruyter]] |page=601}}</ref>{{r|ley196802}} It may be a variant of the word {{lang|de|Molch}} 'salamander'.<ref name="Seebold" /><ref>{{Cite web |url=http://www.dwds.de/?view=1&qu=olm |title=Olm |language=de |website=Digitale Wörterbuch der deutschen Sprache |access-date=2015-12-09}}</ref>

=== Common names ===
It is also called the "human fish" by locals because of its fleshy skin color (translated literally from {{langx|sl|človeška ribica}}, {{langx|mk|човечка рипка}}, {{langx|hr|čovječja ribica}}, {{langx|bs|čovječija ribica}}, {{langx|sr|човечја рибица}}), as well as "cave salamander" or "white salamander".<ref name="NHM">{{Cite web |url=http://www.nhm.ac.uk/kids-only/life/life-dark/olm/ |title=Olm |website=nhm.ac.uk |publisher=[[Natural History Museum, London]] |access-date=2013-07-15}}</ref> In Slovenia, it is called ''močeril'' (from *''močerъ'' 'earthworm, damp creepy-crawly'; ''moča'' 'dampness').<ref>{{Cite book |last=Snoj |first=Marko |title=Slovenski etimološki slovar |date=2003 |publisher=Modrijan |location=Ljubljana |page=408}}</ref><ref>{{Cite book |last=Bezlaj |first=France |title=Etimološki slovar slovenskega jezika, vol. 2 |date=1982 |publisher=SAZU |location=Ljubljana |page=190}}</ref>

== Description ==
===External appearance===
[[File:Protée aveugle.jpg|thumb|The olm as depicted by the French biologist [[Gaston Bonnier]] in 1907]]
The olm's body is [[snake]]like, {{convert|20|–|30|cm|in|round=0.5|abbr=on}} long, with some specimens reaching up to {{convert|40|cm|in|0}}, which makes them some of the largest cave-dwelling animals in the world.<ref name="WEB01">Weber A. (2000). ''Fish and amphibia''. In: Culver D.C. ''et al.'' (ed.): ''Ecosystems of the world: Subterranean Ecosystems'', pp. 109–132. Amsterdam: [[Elsevier]]</ref><ref>{{Cite web|url=https://www.theguardian.com/environment/2017/aug/27/slovenia-baby-dragons-postojna-salamaders-olms-proteus-anguinus|title=How Slovenia is helping its 'baby dragons'|first=Robin|last=McKie|date=August 27, 2017|via=The Guardian}}</ref> The average length is between 23 and 25&nbsp;cm.<ref name="blackburn">{{Cite journal |last=Blackburn |first=Daniel G. |date=2019-07-01 |title=The oviparous olm: Analysis and refutation of claims for viviparity in the cave salamander ''Proteus anguinus'' (Amphibia: Proteidae) |url=https://www.sciencedirect.com/science/article/pii/S0044523119300555 |journal=Zoologischer Anzeiger |language=en |volume=281 |pages=16–23 |doi=10.1016/j.jcz.2019.05.004 |bibcode=2019ZooAn.281...16B |s2cid=190885637 |issn=0044-5231|url-access=subscription }}</ref> Females grow larger than males, but otherwise the primary external difference between the sexes is in the [[cloaca]] region (shape and size) when breeding.<ref name="AW" /> The trunk is cylindrical, uniformly thick, and segmented with regularly spaced furrows at the [[myomere]] borders. The [[tail]] is relatively short, laterally flattened, and surrounded by a thin fin. The limbs are small and thin, with a reduced number of digits compared to other amphibians: the front legs have three digits instead of the normal four, and the rear have two digits instead of five. Its body is covered by a thin layer of skin, which contains very little of the [[biological pigment|pigment]] [[riboflavin]],<ref>{{Cite journal |last1=Istenic L. |last2=Ziegler I. |name-list-style=amp |date=1974 |title=Riboflavin as "pigment" in the skin of ''Proteus anguinus'' L. |journal=Naturwissenschaften |volume=61 |issue=12 |pages=686–687 |bibcode=1974NW.....61..686I |doi=10.1007/bf00606524 |pmid=4449576|s2cid=28710659 }}</ref> making it yellowish-white or pink in color.<ref name="animal" />

The white skin color of the olm retains the ability to produce [[melanin]], and will gradually turn dark when exposed to light; in some cases the [[larva]]e are also colored. One population, the [[black olm]], is always pigmented and dark brownish to blackish when adult.<ref name="SA01"/> The olm's pear-shaped head ends with a short, dorsoventrally flattened snout. The mouth opening is small, with tiny [[tooth|teeth]] forming a [[sieve]] to keep larger particles inside the mouth. The nostrils are so small as to be imperceptible, but are placed somewhat [[Anatomical terms of location#Left and right (lateral), and medial|laterally]] near the end of the snout. The regressed [[eye]]s are covered by a layer of skin. The olm breathes with external [[gill]]s that form two branched tufts at the back of the head.<ref name="animal" /> They are red in color because the oxygen-rich [[blood]] shows through the non-pigmented skin.{{r|ley196802}} The olm also has rudimentary [[lung]]s, but their role in respiration is only accessory, except during [[Hypoxia (environmental)|hypoxic]] conditions.<ref name="AW" />

===Sensory organs===
Cave-dwelling animals have been prompted, among other adaptations, to develop and improve non-visual sensory systems in order to orient in and adapt to permanently dark habitats.<ref name="Schlegal 2006">{{cite journal | last1 = Schlegel | first1 = P.A. | last2 = Briegleb | first2 = W. | last3 = Bulog | first3 = B. | last4 = Steinfartz | first4 = S. | date = 2006 | language =  French | title = Revue et nouvelles données sur la sensitivité a la lumiere et orientation non-visuelle chez Proteus anguinus, Calotriton asper et Desmognathus ochrophaeus (Amphibiens urodeles hypogés) | journal = Bulletin de la Société herpétologique de France | volume = 118 | pages = 1–31 | url = https://pub.uni-bielefeld.de/record/1870980}}</ref> The olm's sensory system is also adapted to life in the subterranean aquatic environment. Unable to use vision for orientation, the olm compensates with other senses, which are better developed than in amphibians living on the surface. It retains larval proportions, like a long, slender body and a large, flattened head, and is thus able to carry a larger number of [[sensory receptor]]s.<ref name="SB01" />

====Photoreceptors====
Although blind, the olm swims away from light.{{r|ley196802}} The eyes are regressed, but retain sensitivity. They lie deep below the [[Dermis|dermis of the skin]] and are rarely visible except in some younger adults. Larvae have normal eyes, but development soon stops and they start regressing, finally atrophying after four months of development.<ref name="DUR01">{{cite journal | last = Durand | first = J.P. | date = 1976 | title = Ocular Development and Involution in the European Cave Salamander, ''Proteus Anguinus'' Laurenti | journal = The Biological Bulletin | volume = 151 | number = 3 | pages = 450–466 | doi = 10.2307/1540499| jstor = 1540499 | pmid = 1016662 | url = https://www.biodiversitylibrary.org/part/13965 }}</ref> The [[pineal body]] also has photoreceptive cells which, though regressed, retain visual pigment like the photoreceptive cells of the regressed eye. The pineal gland in ''Proteus'' probably possesses some control over the physiological processes.<ref name="LANG01">Langecker T.G. (2000). ''The effects of continuous darkness on cave ecology and cavernicolous evolution''. In: Culver D.C. ''et al.'' (eds.): ''Ecosystems of the world: Subterranean Ecosystems'', pp. 135–157. Amsterdam: Elsevier</ref> [[Ethology|Behavioral]] experiments revealed that the skin itself is also sensitive to light.<ref name="HAW01">{{Cite journal |last=Hawes |first=R.S. |date=1945 |title=On the eyes and reactions to light of Proteus anguinus |journal=Q. J. Microsc. Sci. |series=New Series |volume=86 |pages=1–53|pmid=21004249 }}</ref> Photosensitivity of the integument is due to the pigment [[melanopsin]] inside specialized cells called [[melanophore]]s. Preliminary immunocytochemical analyses support the existence of photosensitive pigment also in the animal's integument.<ref name="KOS01">Kos M. (2000). {{lang|sl|Imunocitokemijska analiza vidnih pigmentov v čutilnih celicah očesa in pinealnega organa močerila (Proteus anguinus, Amphibia, Urodela)}} (''Immunocitochemical analysis of the visual pigments in the sensory cells of the eye and the pineal organ of the olm (Proteus anguinus, Amphibia, Urodela).'') PhD thesis. Ljubljana: [[University of Ljubljana]]. {{in lang|sl}}</ref><ref>{{Cite journal |last1=Kos |first1=M. |last2=Bulog |first2=B. |display-authors=etal |date=2001 |title=Immunocytochemical demonstration of visual pigments in the degenerate retinal and pineal photoreceptors of the blind cave salamander (''Proteus anguinus'') |journal=Cell Tissue Res |volume=303 |issue=1 |pages=15–25 |doi=10.1007/s004410000298 |pmid=11236001|s2cid=30951738 }}</ref>

====Chemoreceptors====
[[Image:P anguinus-head1.jpg|thumb|right|The front part of the olm's head carries sensitive chemo-, mechano-, and electroreceptors.]]

The olm is capable of sensing very low concentrations of organic compounds in the water. They are better at sensing both the quantity and quality of prey by smell than related amphibians.<ref name="HUP01">Hüpop K. (2000). ''How do cave animals cope with the food scarcity in caves?''. In: Culver D.C. ''et al.'' (ed.): ''Ecosystems of the world: Subterranean Ecosystems'', pp. 159–188. Amsterdam: Elsevier</ref> The nasal [[epithelium]], located on the inner surface of the nasal cavity and in the [[Jacobson's organ]], is thicker than in other amphibians.<ref name="DC01">{{cite journal | last1 = Dumas | first1 = P | year = 1998 | title = The olfaction in Proteus anguinus | journal = Behavioural Processes | volume = 43 | issue = 2| pages = 107–113 | doi = 10.1016/s0376-6357(98)00002-3 | pmid = 24895999 | s2cid = 20825148 }}</ref> The [[taste buds]] are in the [[mucus|mucous]] epithelium of the mouth, most of them on the upper side of the [[tongue]] and on the entrance to the gill cavities. Those in the oral cavity are used for tasting food, where those near the gills probably sense chemicals in the surrounding water.<ref>{{Cite journal |last1=Istenič |first1=L. |last2=Bulog |first2=B. |year=1979 |title=The structural differentiations of the buccal and pharyngeal mucous membrane of the Proteus anguinus Laur |journal=Biološki Vestnik |volume=27 |pages=1–12}}</ref>

====Mechano- and electroreceptors====
The sensory [[epithelia]] of the [[inner ear]] are very specifically differentiated, enabling the olm to receive [[sound]] waves in the water, as well as [[vibration]]s from the ground. The complex functional-morphological orientation of the sensory cells enables the animal to register the sound sources.<ref>{{Cite journal |last=Bulog |first=B |date=1989 |title=Differentiation of the inner ear sensory epithelia of Proteus anguinus (Urodela, Amphibia) |journal=Journal of Morphology |volume=202 |issue=3 |pages=325–338 |doi=10.1002/jmor.1052020303 |pmid=29865674|s2cid=46928861 }}</ref><ref name="BUL01">Bulog B. (1990). {{lang|sl|Čutilni organi oktavolateralnega sistema pri proteju Proteus anguinus (Urodela, Amphibia). I. Otični labirint}} (''Sense organs of the octavolateral system in proteus Proteus anguinus (Urodela, Amphibia). I. Otic labyrinth''). Biološki vestnik '''38''': 1–16 {{in lang|sl}}</ref> As this animal stays [[neotenic]] throughout its long life span, it is only occasionally exposed to normal adult hearing in air, which is probably also possible for ''Proteus'' as in most salamanders. Hence, it would be of adaptive value in caves, with no vision available, to profit from underwater hearing by recognizing particular sounds and eventual localization of prey or other sound sources, i.e. acoustical orientation in general.
Behavioural (ethological) tests have shown that its sensitivity for detecting underwater sound waves reaches into the area of frequencies of sound waves between 10 and more than 12,000 Hz, while the greatest sensitivity is reached between  1,500 and 2,000 Hz. The ethological experiments indicate that the best hearing sensitivity of ''Proteus'' is between 10&nbsp;Hz and up to 12,000&nbsp;Hz.<ref name="Bulog and Schlegel 2000">Bulog B. & Schlegel P. (2000). ''Functional morphology of the inner ear and underwater audiograms of Proteus anguinus (Amphibia, Urodela)''. Pflügers Arch '''439'''(3), suppl., pp. R165–R167.</ref> The [[lateral line]] supplements inner ear sensitivity by registering low-frequency nearby water displacements.<ref name="Schlegal 2006" /><ref name="Bulog and Schlegel 2000" />

A new type of [[electroreception]] sensory organ has been analyzed on the head of ''Proteus'', utilizing light and [[Electron microscope|electron microscopy]]. These new organs have been described as [[ampullary organ]]s.<ref>{{Cite journal |last1=Istenič |first1=L. |last2=Bulog |first2=B. |date=1984 |title=''Some evidence for the ampullary organs in the European cave salamander Proteus anguinus'' (Urodela, Amphibia) |journal=Cell Tissue Res |volume=235 |issue=2 |pages=393–402 |doi=10.1007/bf00217865 |pmid=6705040|s2cid=25511603 }}</ref>

Like some other lower [[vertebrate]]s, the olm has the ability to register weak [[electric field]]s.<ref name="SB01">{{Cite journal |last1=Schlegel |first1=P. |last2=Bulog |first2=B. |date=1997 |title=Population-specific behavioral electrosensitivity of the European blind cave salamander, Proteus anguinus |journal=Journal of Physiology (Paris) |volume=91 |issue=2 |pages=75–79 |doi=10.1016/S0928-4257(97)88941-3 |pmid=9326735|s2cid=25550328 }}</ref> Some behavioral experiments suggest that the olm may be able to use Earth's [[magnetic field]] to orient itself. In 2002, ''Proteus'' ''anguinus'' was found to align itself with natural and artificially modified magnetic fields.<ref>Bulog B., Schlegel P. ''et al.'' (2002). ''Non-visual orientation and light-sensitivity in the blind cave salamander, ''Proteus'' anguinus'' (Amphibia, Caudata). In: Latella L., Mezzanotte E., Tarocco M. (eds.). 16th international symposium of biospeleology; 2002 Sep 8–15; Verona: Societé Internationale de Biospéologie, pp. 31–32.</ref>

==Ecology and life history==
[[file:P anguinus1.jpg|thumb|The olm swims by serpentine bending of the body.]]

The olm lives in well-oxygenated underground waters with a typical, very stable temperature of {{convert|8-11|C|F|abbr=on}}, infrequently as warm as {{convert|14|C|F|abbr=on}}.<ref name="AW" /> There have also been observations in northeastern Italy where they swim to the surface in springs outside the caves, even in daylight, where they occasionally feed on earthworms.<ref>{{cite journal |last1=Manenti |first1=Raoul |title=Wandering outside of the Styx: Surface activity of an iconic subterranean vertebrate, the olm (Proteus anguinus) |journal=The Scientific Naturalist |date=February 8, 2024 |volume=105 |issue=3 |pages=e4252 |doi=10.1002/ecy.4252 |pmid=38329178 |bibcode=2024Ecol..105E4252M |url=https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.4252 |access-date=25 April 2024|hdl=2434/1036228 |hdl-access=free }}</ref> The black olm may occur in surface waters that are somewhat warmer.<ref name="AW" />

[[Image:P anguinus-head.jpg|thumb|right|Disproportionately elongated head with gills]]

The olm swims by eel-like twisting of its body, assisted only slightly by its poorly developed legs. It is a [[predator]]y animal, feeding on small [[crustacean]]s (for example, ''[[Troglocaris]]'' shrimp, ''[[Niphargus]]'', ''[[Asellus]]'', and ''Synurella'' amphipods, and ''[[Oniscus asellus]]''), [[snail]]s (for example, ''[[Belgrandiella]]''), and occasionally [[insect]]s and insect larvae (for example, [[Trichoptera]], [[Ephemeroptera]], [[Plecoptera]], and [[Diptera]]).<ref name="animal" /><ref name="Jugovic2015">{{Cite journal |last1=Jugovic E. |last2=J.E. Praprotnik |last3=V. Buzan |last4=M. Lužnik |year=2015 |title=Estimating population size of the cave shrimp Troglocaris anophthalmus (Crustacea, Decapoda, Caridea) using mark–release–recapture data |journal=Animal Biodiversity and Conservation |volume=38 |issue=1 |pages=77–86|doi=10.32800/abc.2015.38.0077 |doi-access=free }}</ref><ref>{{cite web | url = https://animaldiversity.org/accounts/Proteus_anguinus/ | title = Proteus anguinus | website = Animal Diversity Web | last = Meaton | first = J. | date = 2011 | access-date = 1 January 2023}}</ref><ref>{{cite web | url = https://amphibiaweb.org/species/4229 | title = Proteus anguinus | website = AmphibiaWeb | date = 2021}}</ref> It does not chew its food, instead swallowing it whole. The olm is resistant to long-term starvation, an adaptation to its underground habitat. It can consume large amounts of food at once, and store nutrients as large deposits of [[lipid]]s and [[glycogen]] in the [[liver]]. When food is scarce, it reduces its activity and [[metabolism|metabolic rate]], and can also reabsorb its own tissues in severe cases. Controlled experiments have shown that an olm can survive up to 10 years without food.<ref name="BUL02">{{Cite journal |last=Bulog |first=B. |date=1994 |title=Dve desetletji funkcionalno-morfoloških raziskav pri močerilu (Proteus anguinus, Amphibia, Caudata) |trans-title=Two decades of functional-morphological research on the olm (''Proteus anguinus, Amphibia, Caudata'') |url=http://www.dlib.si/details/URN:NBN:SI:DOC-VJMGI7ZT |journal=Acta Carsologica |language=sl |volume=23 |pages=248–263}}</ref>

Olms are [[Social animal|gregarious]], and usually aggregate either under stones or in fissures.<ref name="GUI01">{{Cite journal |last=Guillaume |first=O |date=2000 |title=Role of chemical communication and behavioural interactions among conspecifics in the choice of shelters by the cave-dwelling salamander Proteus anguinus (Caudata, Proteidae) |journal=Can. J. Zool. |volume=78 |issue=2 |pages=167–173 |doi=10.1139/z99-198|bibcode=2000CaJZ...78..167G }}</ref> Sexually active males are an exception, establishing and defending territories where they attract females. The scarcity of food makes fighting energetically costly, so encounters between males usually only involve [[Display (zoology)|display]]. This is a behavioral adaptation to life underground.<ref name="ALJ01" />

===Breeding and longevity===
Reproduction has only been observed in captivity so far.<ref name="ALJ01" /><ref>{{cite journal | last=Aljančič | first=Gregor | title=History of research on ''Proteus anguinus'' Laurenti 1768 in Slovenia | journal=Folia Biologica et Geologica | volume=60 | issue=1 | date=2019-07-25 | doi=10.3986/fbg0050 | page=39| doi-access=free }}</ref> Sexually mature males have swollen cloacas, brighter skin color, two lines at the side of the tail, and slightly curled fins. No such changes have been observed in the females. The male can start courtship even without the presence of a female. He chases other males away from the chosen area, and may then secrete a female-attracting [[pheromone]]. When the female approaches, he starts to circle around her and fan her with his tail. Then he starts to touch the female's body with his snout, and the female touches his cloaca with her snout. At that point, he starts to move forward with a twitching motion, and the female follows. He then deposits the [[spermatophore]], and the animals keep moving forward until the female hits it with her cloaca, after which she stops and stands still. The spermatophore sticks to her and the [[sperm]] cells swim inside her cloaca, where they attempt to fertilize her eggs. The courtship ritual can be repeated several times over a couple of hours.<ref name="ALJ01" />

The female lays up to 70 eggs, each about {{convert|12|mm|in|1}} in diameter, and places them between rocks, where they remain under her protection.<ref name="AA01">{{cite journal|last1=Aljančič |first1=G.|last2= Aljančič |first2=M. |year=1998|url=https://www.tular.si/images/pdf/GM_Aljancic_1998_Razmnozevanje_cloveske_ribice.pdf |title=Žival meseca oktobra: Človeška ribica (Proteus anguinus) |trans-title=The animal of the month of October: olm|journal=Proteus|volume=61|issue=2|pages=83–87|lang=sl}}</ref> The average is 35 eggs and the adult female typically breeds every 12.5 years.<ref name="Voituron2010">{{Cite journal |last1=Voituron |first1=Y. |last2=De Fraipont |first2=M. |last3=Issartel |first3=J. |last4=Guillaume |first4=O. |last5=Clobert |first5=J. |year=2010 |title=Extreme lifespan of the human fish (Proteus anguinus): a challenge for ageing mechanisms |journal=Biology Letters |volume=7 |issue=1 |pages=105–107 |doi=10.1098/rsbl.2010.0539 |pmc=3030882 |pmid=20659920}}</ref> The tadpoles are {{convert|2|cm|in|1}} long when they hatch and live on [[yolk]] stored in the cells of the digestive tract for a month.<ref name="AA01" />

At a temperature of {{convert|10|C|F|abbr=on}}, the olm's [[embryo]]nic development (time in the eggs before hatching) is 140 days, but it is somewhat slower in colder water and faster in warmer, being as little as 86 days at {{convert|15|C|F|abbr=on}}. After hatching, it takes another 14 years to reach sexual maturity if living in water that is {{convert|10|C|F|abbr=on}}.<ref name="AW" /><ref name="DUR02">{{Cite journal |last1=Durand |first1=J.P. |last2=Delay |first2=B. |date=1981 |title=Influence of temperature on the development of ''Proteus anguinus'' (Caudata: Proteidae) and relation with its habitat in the subterranean world |journal=Journal of Thermal Biology |volume=6 |issue=1 |pages=53–57 |doi=10.1016/0306-4565(81)90044-9|bibcode=1981JTBio...6...53D }}</ref> The larvae gain adult appearance after nearly four months, with the duration of development strongly correlating with water temperature.<ref name="DUR02" /> Unconfirmed historical observations of [[viviparity]] exist, but it has been shown that the females possess a [[gland]] that produces the egg casing, similar to those of [[fish]] and egg-laying amphibians.<ref name="ALJ01">Aljančič M., Bulog B. et al. (1993). ''Proteus&nbsp;– mysterious ruler of Karst darkness''. Ljubljana: Vitrium d.o.o. {{in lang|sl}}</ref> [[Paul Kammerer]] reported that female olm gave birth to live young in water at or below {{convert|55|F|C|abbr=on|order=flip}} and laid eggs at higher,{{r|ley196802}} but rigorous observations have not confirmed that. Historical reports of viviparity have long been attributed to scientific fraud, but may have alternatively resulted from the olms tendency to regurgitate food due to stress. These food items, including juvenile salamanders, may have been misinterpreted as their offspring.<ref>{{Cite journal |last=Recknagel |first=Hans |last2=Premate |first2=Ester |last3=Zakšek |first3=Valerija |last4=Aljančič |first4=Gregor |last5=Kostanjšek |first5=Rok |last6=Trontelj |first6=Peter |date=2022-04-07 |title=Oviparity, viviparity or plasticity in reproductive mode of the olm Proteus anguinus: an epic misunderstanding caused by prey regurgitation? |url=https://brill.com/view/journals/ctoz/91/3/article-p153_001.xml |journal=Contributions to Zoology |volume=91 |issue=3 |pages=153–165 |doi=10.1163/18759866-bja10029 |issn=1875-9866}}</ref> Regardless, the olm appears to be exclusively [[ovipary|oviparous]].<ref>{{Cite book |title=Reproductive biology and phylogeny of Urodela |date=2003 |publisher=Science Publishers |isbn=1578082854 |editor-last=Sever, David M. |page=449}}</ref>

Development of the olm and other [[troglobite]] amphibians is characterized by [[heterochrony]]&nbsp;– the animal does not undergo [[metamorphosis]] and instead retains larval features. The form of heterochrony in the olm is [[neoteny]]&nbsp;– delayed [[Somatic (biology)|somatic]] maturity with precocious reproductive maturity, i.e. reproductive maturity is reached while retaining the larval external [[morphology (biology)|morphology]]. In other amphibians, the metamorphosis is regulated by the [[hormone]] [[thyroxine]], secreted by the [[thyroid]] gland. The thyroid is normally developed and functioning in the olm, so the lack of metamorphosis is due to the unresponsiveness of key [[Tissue (biology)|tissues]] to thyroxine.<ref name="LANG01" />

Longevity is estimated at up to 58 years.<ref>Noellert A., Noellert C. (1992). ''Die Aphibien Europas''. Franckh-Kosmos Verlags GmbH & co., Stuttgart.{{in lang|de}}</ref> A study published in ''[[Biology Letters]]'' estimated that they have a maximum lifespan of over 100 years and that the lifespan of an average adult is around 68.5 years. When compared to the longevity and body mass of other amphibians, olms are [[outlier]]s, living longer than would be predicted from their size.<ref name=Voituron2010/>

==Taxonomic history==
Olms from different cave systems differ substantially in body measurements, color, and some microscopic characteristics. Earlier researchers used these differences to support the division into five species, while modern herpetologists understand that external morphology is not reliable for amphibian systematics and can be extremely variable, depending on nourishment, illness, and other factors; even varying among individuals in a single [[population]]. ''Proteus anguinus'' is now considered a single species. The length of the head is the most obvious difference between the various populations&nbsp;– individuals from Stična, Slovenia, have shorter heads on average than those from [[Tržič]], Slovenia, and the [[Istria]]n peninsula, for example.<ref>{{Cite journal |last1=Arntzen |first1=J.W. |last2=Sket |first2=Boris |date=1997 |title=Morphometric analysis of black and white European cave salamanders, Proteus anguinus |journal=Journal of Zoology |volume=241 |issue=4 |pages=699–707 |doi=10.1111/j.1469-7998.1997.tb05742.x}}</ref>

===Black olm===
[[Image:P anguinus parkelj-head.jpg|thumb|right|The black olm, a subspecies, has a shorter head with more-developed eyes compared to the nominate subspecies.]]
[[Image:Researchventhole.jpg|thumb|right|The research vent-hole in Jelševnik near Črnomelj, where quality checks of water and sediments are performed regularly, and where activities of black olms are registered with an [[Infrared|IR]] camera]]
The '''black olm''' ('''''Proteus anguinus parkelj''''' <small>Sket & Arntzen, 1994</small>) is the only recognized [[subspecies]] of the olm other than the [[nominate subspecies]]<!--A species either has no subspecies or at least two. The other (nominate) subspecies is mentioned both above and below!-->. It is [[endemism|endemic]] to the underground waters near [[Črnomelj]], Slovenia, an area smaller than {{convert|100|km2|sqmi|0}}. It was first found in 1986 by members of the [[Slovenian Karst Research Institute]], who were exploring the water from [[Dobličica|Dobličica karst spring]] in the [[White Carniola]] region.<ref name="ZSLO01">Sket B. ''et al.'' (ed.) (2003). {{lang|sl|Živalstvo Slovenije}} (''The animals of Slovenia''). Ljubljana: [[Tehniška založba Slovenije]]. {{ISBN|86-365-0410-4}} {{in lang|sl}}</ref>

It has several features separating it from the [[nominotypical subspecies]] (''Proteus a. anguinus''):<ref name="SA01">{{Cite journal |last1=Sket |first1=B. |last2=Arntzen |first2=J.W. |date=1994 |title=A black, non-troglomorphic amphibian from the karst of Slovenia: Proteus anguinus parkelj n. ssp (Urodela: Proteidae) |journal=Bijdragen tot de Dierkunde |volume=64 |pages=33–53 |doi=10.1163/26660644-06401002|doi-access=free }}</ref>
{| class="wikitable"
|-
!Feature!!''Proteus anguinus anguinus''!!''Proteus anguinus parkelj''!!Notes
|-
!  style="text-align:left; vertical-align:top;"| Skin
| valign="top"|Not pigmented. || Normally pigmented, dark brown, or black in color. || valign="top"| The most obvious difference.
|-
!  style="text-align:left; vertical-align:top;"| Head shape
| valign="top"| Long, slender. || Shorter, equally thick. Stronger jaw muscles visible as two bulbs on the top of the head.
|-
!  style="text-align:left; vertical-align:top;"| Body length
| valign="top"| Shorter, 29–32 [[vertebra]]e. || valign="top"| Longer, 34–35 vertebrae. || Amphibians do not have a fixed number of vertebrae.
|-
!  style="text-align:left; vertical-align:top;"| Appendages
| valign="top"| Longer. || valign="top"| Shorter. ||
|-
!  style="text-align:left; vertical-align:top;"| Tail
| valign="top"| Longer in proportion to the rest of the body. || valign="top"| Shorter in proportion.
|-
!  style="text-align:left; vertical-align:top;"| Eyes
| valign="top"| Regressed. || valign="top" | Almost normally developed, although still small compared to other amphibians. Covered by a thin layer of transparent skin, no eyelids. || valign="top"| Regressed eye of White Proteus shows first of all immunolabelling for the red-sensitive cone opsin. The eye of Black ''Proteus'' has principal rods, red-sensitive cones and blue- or [[UV]]- sensitive cones.
|-
! style="text-align:left;"| Other senses
| valign="top"| Specific and highly sensitive. || valign="top"| Some sensory organs, particularly electroreceptors, less sensitive.|| valign="top"| Not very obvious.
|}

=== ''Proteus bavaricus'' ===
A potential species, ''Proteus bavaricus'', is speculated to be closely related to ''P. anguinus''.<ref>{{Cite journal |last1=Macaluso |first1=Loredana |last2=Villa |first2=Andrea |last3=Mörs |first3=Thomas |date=2022 |editor-last=Mannion |editor-first=Philip |title=A new proteid salamander (Urodela, Proteidae) from the middle Miocene of Hambach (Germany) and implications for the evolution of the family |url=https://onlinelibrary.wiley.com/doi/10.1111/pala.12585 |journal=Palaeontology |language=en |volume=65 |issue=1 |page=12585 |doi=10.1111/pala.12585 |bibcode=2022Palgy..6512585M |issn=0031-0239|hdl=2318/1825718 |hdl-access=free }}</ref> [[Species description|The species was described]] from a single bone by George Brunner, and the [[holotype]] is housed in his private collection.<ref>{{Cite book |url=https://books.google.com/books?id=FNNFAAAAYAAJ&q=%22Proteus+bavaricus%22 |title=Handbuch der Paläoherpetologie: Encyclopedia of paleoherpetology |date=1981 |publisher=G. Fischer |isbn=978-3-437-30339-5 |language=en}}</ref><ref name=":0">{{Cite book |last=Holman |first=J. Alan |url=https://books.google.com/books?id=mXzODd-3pD4C&dq=%22Proteus+bavaricus%22&pg=PA23 |title=Pleistocene Amphibians and Reptiles in Britain and Europe |date=1998-06-18 |publisher=Oxford University Press |isbn=978-0-19-535466-9 |language=en}}</ref> It was found in [[Bavaria]]'s [[Devil's Cave (Pottenstein)|Devil's Cave]], in the [[Pleistocene]] layer.<ref name=":0" /> In his 1998 book, J. Alan Hollman described the species as a "problematic" taxon, saying that Brunner's drawing of the bone does not adequately show the differences between ''P. bavaricus'' and ''P. anguinus''.<ref name=":0" />

==Research history==
The first written mention of the olm is in [[Johann Weikhard von Valvasor]]'s ''[[The Glory of the Duchy of Carniola]]'' (1689) as a baby [[dragon]]. Heavy rains of Slovenia would wash the olms up from their subterranean habitat, giving rise to the folklore belief that great dragons lived beneath the Earth's crust, and the olms were the undeveloped offspring of these mythical beasts. In his book Valvasor compiled the local Slovenian folk stories and pieced together the rich mythology of the creature and documented observations of the olm as "Barely a span long, akin to a lizard, in short, a worm and vermin of which there are many hereabouts".
<ref name="ley196802">{{Cite magazine
 |last=Ley
 |first=Willy
 |date=February 1968
 |title=Epitaph for a Lonely Olm
 |department=For Your Information
 |url=https://archive.org/stream/Galaxy_v26n03_1968-02_modified#page/n37/mode/2up
 |magazine=Galaxy Science Fiction
 |pages=95–104
}}</ref><ref name="Nick Baker: Naturalist">{{Cite web |url=http://www.nickbaker.tv/feature-creature/ |title=The Dragon of Vrhnika&nbsp;– The Olm |last=Baker |first=Nick |author-link=Nick Baker (naturalist) |website=Nickbaker.tv |url-status=dead |archive-url=https://web.archive.org/web/20091212155936/http://www.nickbaker.tv/feature-creature/ |archive-date=2009-12-12 |access-date=2009-12-05}}</ref>

[[File:Proteus - Laurenti.jpg|thumb|Sketch of the olm in ''Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena'' (1768) by [[Josephus Nicolaus Laurenti]]]]
The first researcher to retrieve a live olm was a physician and researcher from [[Idrija]], [[Giovanni Antonio Scopoli]], who sent dead specimens and drawings to colleagues and collectors. [[Josephus Nicolaus Laurenti]], though, was the first to briefly describe the olm in 1768 and give it the scientific name ''Proteus anguinus''. It was not until the end of the century that [[Carl Franz Anton Ritter von Schreibers]] from the [[Naturhistorisches Museum]] of [[Vienna]] started to look into this animal's anatomy. The specimens were sent to him by [[Sigmund Zois]]. Schreibers presented his findings in 1801 to The [[Royal Society]] in [[London]], and later also in [[Paris]]. Soon, the olm started to gain wide recognition and attract significant attention, resulting in thousands of animals being sent to researchers and collectors worldwide. A Dr Edwards was quoted in a book of 1839 as believing that "...the Proteus Anguinis is the first stage of an animal prevented from growing to perfection by inhabiting the subterraneous waters of Carniola."<ref>{{Cite book |last=Millingen |first=J. G. |url=https://books.google.com/books?id=Ld0phxi03A4C&q=dr+edwards+Proteus+Anguinis&pg=PT28 |title=Curiosities of Medical Experience |date=1839 |publisher=Richard Bentley |isbn=9781465521750 |edition=2nd |location=London |access-date=8 March 2018}}</ref>

In 1880 Marie von Chauvin began the first long-term study of olms in captivity. She learned that they detected prey's motion, panicked when a heavy object was dropped near their habitat, and developed color if exposed to weak light for a few hours a day, but could not cause them to change to a land-dwelling adult form, as she and others had done with [[axolotl]].{{r|ley196802}}

The basis of functional morphological investigations in Slovenia was set up by {{ill|Lilijana Istenič|de}} in the 1980s. More than twenty years later, the Research Group for functional morphological Studies of the Vertebrates in the Department of Biology (Biotechnical Faculty, [[University of Ljubljana]]), is one of the leading groups studying the olm under the guidance of [[Boris Bulog]].<ref>Bulog B. et al. (2003). ''Black Proteus: mysterious dweller of the Karst in Bela krajina''. Ljubljana: TV Slovenia, Video tape.</ref> There are also several cave laboratories in Europe in which olms have been introduced and are being studied. These are [[Moulis, Ariège]] ([[France]]), [[Choranche  cave]] ([[France]]), [[Caves of Han-sur-Lesse|Han-sur-Lesse]] ([[Belgium]]), and [[Aggtelek (town)|Aggtelek]] ([[Hungary]]). They were also [[Introduced species|introduced]] into the [[Hermannshöhle]] ([[Germany]]) and [[Oliero]] ([[Italy]]) caves, where they still live today.<ref>{{Cite book |last=Grosse |first=Wolf-Rüdiger |title=Die Lurche und Kriechtiere Sachsen-Anhalts |date=2004 |publisher=Laurenti-Verlag |isbn=3-933066-17-4 |editor-last=Frank Meyer |location=Bielefeld |pages=191–193 |chapter=Grottenolm – Proteus anguinus Laurenti, 1768 |display-editors=etal}}</ref><ref>{{Cite book |last1=Bonato |first1=Lucio |title=Atlante degli anfibi e dei rettili del Veneto |last2=Fracasso |first2=Giancarlo |last3=Pollo |first3=Roberto |last4=Richard |first4=Jacopo |last5=Semenzato |first5=Massimo |date=2007 |publisher=Nuova Dimensione Edizioni |isbn=9788889100400 |pages=71&ndash;73 |chapter=Proteo}}</ref> Additionally, there is evidence that a small number of olms were introduced to the United Kingdom in the 1940s, although it's highly likely that the animals perished shortly after being released.<ref>{{cite journal |last1=Lewarne |first1=Brian |last2=Allain |first2=Steven J. R. |date=2020 |title=The unnatural history of cave olms ''Proteus anguinus'' in England |journal=Herpetological Bulletin |volume= 154 |issue=154, Winter 2020 |pages=18–19 |doi=10.33256/hb154.1819|doi-access=free }}</ref>

The olm was used by [[Charles Darwin]] in his seminal work ''[[On the Origin of Species]]'' as an example for the reduction of structures through disuse:<ref name="DARWIN01">Darwin C. (1859). ''On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life''. London: John Murray.</ref>

{{blockquote|Far from feeling surprise that some of the cave-animals should be very anomalous...as is the case with blind Proteus with reference to the reptiles of Europe, I am only surprised that more wrecks of ancient life have not been preserved, owing to the less severe competition to which the scanty inhabitants of these dark abodes will have been exposed.}}An olm (Proteus) genome project is currently underway by the [[University of Ljubljana]] and [[BGI Group|BGI]]. With an estimated genome size roughly 15-times the size of human genome, this will likely be the largest [[List of sequenced animal genomes|animal genome]] sequenced so far<ref>{{Cite web |url=https://www.proteusgenome.com/ |title=Home |website=Proteus genome project |language=en-US |access-date=2020-01-29}}</ref> at nearly 50 [[gigabase]]s.<ref>{{Cite journal|url=https://nyaspubs.onlinelibrary.wiley.com/doi/epdf/10.1111/nyas.14686|title=Toward the massive genome of Proteus anguinus—illuminating longevity, regeneration, convergent evolution, and metabolic disorders|date=2022 |via=nyaspubs.onlinelibrary.wiley.com|doi=10.1111/nyas.14686 |last1=Kostanjšek |first1=Rok |last2=Diderichsen |first2=Børge |last3=Recknagel |first3=Hans |last4=Gunde-Cimerman |first4=Nina |last5=Gostinčar |first5=Cene |last6=Fan |first6=Guangyi |last7=Kordiš |first7=Dušan |last8=Trontelj |first8=Peter |last9=Jiang |first9=Hui |last10=Bolund |first10=Lars |last11=Luo |first11=Yonglun |journal=Annals of the New York Academy of Sciences |volume=1507 |issue=1 |pages=5–11 |pmid=34480358 |bibcode=2022NYASA1507....5K }}</ref>

==Conservation==
The olm is extremely vulnerable to changes in its environment, due to its adaptation to the specific conditions in caves. Water resources in the karst are extremely sensitive to all kinds of pollution.<ref>{{Cite journal |last1=Bulog |first1=B. |last2=Mihajl |first2=K. |display-authors=etal |date=2002 |title=Trace element concentrations in the tissues of Proteus anguinus (Amphibia, Caudata) and the surrounding environment |journal=Water, Air, & Soil Pollution |volume=136 |issue=1–4 |pages=147–163 |doi=10.1023/A:1015248110142|s2cid=55129952 }}</ref> The contamination of the karst underground waters is due to the large number of waste disposal sites leached by rainwater, as well as to the accidental overflow of various liquids. The reflection of such pollution in the karst underground waters depends on the type and quantity of pollutants, and on the rock structure through which the waters penetrate. Self-purification processes in the underground waters are not completely understood, but they are quite different from those in surface waters.<ref name="CastanoSanchez2020">{{cite journal | last1=Castaño-Sánchez | first1=Andrea | last2=Hose | first2=Grant C. | last3=Reboleira | first3=Ana Sofia P.S. | title=Ecotoxicological effects of anthropogenic stressors in subterranean organisms: A review | journal=Chemosphere | volume=244 | year=2020 | doi=10.1016/j.chemosphere.2019.125422 | page=125422| pmid=31805461 | bibcode=2020Chmsp.24425422C }}</ref>

Among the most serious chemical [[pollutants]] are chlorinated hydrocarbon [[pesticide]]s, [[fertilizer]]s, [[polychlorinated biphenyls]] (PCBs), which are or were used in a variety of industrial processes and in the manufacture of many kinds of materials; and metals such as mercury, lead, cadmium, and arsenic. All of these substances persist in the environment, being slowly, if at all, degraded by natural processes. In addition, all are toxic to life if they accumulate in any appreciable quantity.<ref name="CastanoSanchez2020"/> The olm is nevertheless noted for its capability of surviving higher concentrations of accumulated PCBs than related aquatic organisms.<ref>{{cite journal | last1=Pezdirc | first1=Marko | last2=Heath | first2=Ester | last3=Bizjak Mali | first3=Lilijana | last4=Bulog | first4=Boris | title=PCB accumulation and tissue distribution in cave salamander (''Proteus anguinus anguinus'', Amphibia, Urodela) in the polluted karstic hinterland of the Krupa River, Slovenia | journal=Chemosphere | volume=84 | issue=7 | year=2011 | doi=10.1016/j.chemosphere.2011.05.026 | pages=987–993| pmid=21658741 | bibcode=2011Chmsp..84..987P }}</ref>

The olm was included in annexes II and IV of the 1992 EU [[Habitats Directive]] (92/43/EEC). The list of species in annex II, combined with the habitats listed in annex I, is used by individual countries to designate [[protected area]]s known as 'Special Areas of Conservation'. These areas, combined with others created by the older [[Birds Directive]] were to form the [[Natura 2000]] network. Annex IV additionally lists "animal and plant species of community interest in need of strict protection", although this has little legal ramifications.<ref name="EEC01">[http://ec.europa.eu/environment/nature/legislation/habitatsdirective/index_en.htm Habitats directive] (1992)  ''ec.europa.eu''</ref> Areas inhabited by the olm were eventually included in the Slovenian, Italian and Croatian parts of the Natura 2000 network.<ref>{{cite web |url=https://eunis.eea.europa.eu/species/775 |title=Olm - Proteus anguinus Laurenti, 1768 |publisher=[[European Environment Agency]] |accessdate=2023-08-19}}</ref>

The olm was first protected in Slovenia in 1922 along with all cave fauna, but the protection was not effective and a substantial black market came into existence. In 1982 it was placed on a list of rare and endangered species. This list also had the effect of prohibiting trade of the species. After joining the [[European Union]] in 2004, Slovenia had to establish mechanisms for protection of the species included in the EU Habitats Directive. The olm is included in a [[Regional Red List|''Slovenian Red list'']] of endangered species, thus its capturing or killing is allowed only under specific circumstances determined by the local authorities (e.g. scientific study).<ref name="UL01">''Slovenian official gazette'' (2002). [http://www.uradni-list.si/_pdf/2002/Ur/u2002082.pdf no. 82, Tuesday 24 September 2002]. {{in lang|sl}}</ref>

In Croatia, the olm is protected by the legislation designed to protect amphibians&nbsp;– collecting is possible only for research purposes by permission of the National Administration for Nature and Environment Protection.<ref name="NN01">{{Cite web |url=http://www.nn.hr/clanci/sluzbeno/1999/1435.htm |title=Pravilnik o zaštiti vodozemaca |last=Državna uprava za zaštitu prirode i okoliša |date=1999 |website=[[Narodne novine]] |language=hr |access-date=2009-12-05}}</ref> As of 2020 the Croatian population has been assessed as '[[critically endangered]]' in Croatia.<ref name=ZagrebZoo>{{cite web| url=https://www.croatiaweek.com/zagreb-zoo-only-one-in-the-world-with-two-rare-species/ | title=Zagreb Zoo only one in the world with two rare species | date=10 January 2020 |language=hr | work=CroatiaWeek.com}}</ref>

{{As of|1999}}, the environmental laws in [[Bosnia and Herzegovina]] and [[Montenegro]] had not yet been clarified for this species.{{update-inline|date=March 2025}}

In the 1980s the [[IUCN]] claimed that some illegal collection of this species for the pet trade took place, but that the extent of this was unknown: this text has been copied into subsequent assessments, but by now the anecdotic claims are not considered to be indicative of a major threat. Since the 1980s until the most recent assessment in 2022 the organisation has rated the conservation status for the [[IUCN Red List]] as '[[vulnerable species|vulnerable]]', this because of its natural distribution being fragmented over a number of cave systems as opposed to being continuous, and what they consider a decline in extent and quality of its habitat, which they assume means that the population has been decreasing for the last 40 years.<ref name="IUCN"/>

[[Zagreb Zoo]] in Croatia houses the olm.<ref name=ZagrebZoo/><ref>{{cite web | url=https://www.jutarnji.hr/vijesti/hrvatska/zagrebacki-zooloski-vrt-jedini-je-na-svijetu-u-kojem-mozete-vidjeti-ove-dvije-zivotinje-posjetitelje-treba-poticati-na-ocuvanje-njihovih-vrsta/9838093/ | title=ZAGREBAČKI ZOOLOŠKI VRT JEDINI JE NA SVIJETU U KOJEM MOŽETE VIDJETI OVE DVIJE ŽIVOTINJE 'Posjetitelje treba poticati na očuvanje njihovih vrsta' | date=10 January 2020 | author=Hina | work=[[Jutarnji list]] | language=hr}}</ref><ref>{{Cite web|title=ČOVJEČJA RIBICA (Proteus anguinus)|url=https://zoo.hr/248002-2/|access-date=16 July 2020|website=Zoo.hr|language=hr}}</ref> Historically, olms were kept in several zoos in Germany, as well as in Belgium, the Netherlands, Slovenia and the United Kingdom. At present they can only be experienced at Zagreb Zoo, [[Hermann's Cave|''Hermannshöhle'']] in Germany and [[Vivarium Proteus]] (Proteus Vivarium) within ''Postojnska jama'' (Postojna Cave) in Slovenia.<ref>{{cite web |url=https://www.zootierliste.de/?klasse=4&ordnung=402&familie=40205&art=3060201 |title=Grottenolm ''Proteus anguinus'' LAURENTI, 1768 |author=<!--Not stated--> |website=Zootierliste |publisher=Zoologischen Gesellschaft für Arten- und Populationsschutz e.V. |language=de |access-date=3 August 2023}}</ref> There are also captive breeding programs in places like France.<ref>{{Cite web |last=Yong |first=Ed |date=2010-07-20 |title=The olm: the blind cave salamander that lives to 100 |url=https://www.nationalgeographic.com/science/article/the-olm-the-blind-cave-salamander-that-lives-to-100 |archive-url=https://web.archive.org/web/20230607080723/https://www.nationalgeographic.com/science/article/the-olm-the-blind-cave-salamander-that-lives-to-100 |archive-date=2023-06-07 |access-date=2023-09-30 |website=National Geographic |language=en}}</ref>

==Cultural significance==
The olm is a symbol of Slovenian natural heritage. The enthusiasm of scientists and the broader public about this inhabitant of Slovenian caves is still strong 300 years after its discovery. [[Postojna Cave]] is one of the birthplaces of [[biospeleology]] due to the olm and other rare cave inhabitants, such as the [[Leptodirus hochenwartii|blind cave beetle]]. The image of the olm contributes significantly to the fame of Postojna Cave, which Slovenia successfully utilizes for the promotion of [[ecotourism]] in [[Postojna]] and other parts of Slovenian karst. Tours of Postojna Cave also include a tour around the speleobiological station&nbsp;– the Proteus [[vivarium]], showing different aspects of the cave environment.<ref name="vivarium">[http://www.postojnska-jama.si/?cat=81&lang=en&PHPSESSID=b59779a3f5babf443ef966f0264dc436 Destinacija Postojna] {{Webarchive|url=https://web.archive.org/web/20070927104433/http://www.postojnska-jama.si/?cat=81&lang=en&PHPSESSID=b59779a3f5babf443ef966f0264dc436 |date=2007-09-27 }}. Retrieved 7 June 2007.</ref>

The olm was also depicted on one of the [[Slovenian tolar]] coins.<ref>{{Cite book |last1=Plut-Pregelj |first1=Leopoldina |title=The A to Z of Slovenia |last2=Rogel |first2=Carole |date=2010 |publisher=Scarecrow Press |isbn=9781461731757 |pages=97–98 |chapter=Currency}}</ref> It was also the namesake of ''Proteus'', the oldest Slovenian popular science magazine, first published in 1933.<ref>{{Cite web |url=http://www.mkk.si/book/proteus/ |title=Proteus |publisher=City Library Kranj |access-date=2014-01-22}}</ref>
{{Clear}}

== Notes ==
{{notelist}}

==References==
{{Reflist|25em}}

==External links==
{{Wikispecies|Proteus anguinus}}
{{Commons category|Proteus anguinus}}
*[http://www.edgeofexistence.org/amphibians/species_info.php?id=563&search=focal EDGE of Existence Olm information]
*[http://www.showcaves.com/english/explain/Biology/ProteusAnguinus.html Flora and Fauna of Caves: Proteus anguinus]
*[http://www.proteus.si/?q=node/1 Proteus magazine] {{in lang|sl}}
*[https://web.archive.org/web/20070524123804/http://camp.rrc-kp.si/praksa/proteus/index_en.htm Slovenian practice example: Human Fish (''Proteus anguinus'')]
*[https://web.archive.org/web/20070517141401/http://www.arkive.org/species/GES/amphibians/Proteus_anguinus/ The olm on ARKive]&nbsp;– pictures, films
*[https://web.archive.org/web/20070815215948/http://www2.pms-lj.si/najpred/proteus.html The olm] on the pages of the Slovenian Natural history museum {{in lang|sl}}
*[https://web.archive.org/web/20070929084057/http://www.globalamphibians.org/servlet/GAA?searchName=Proteus+anguinus The Global Amphibian Assessment&nbsp;– Proteus anguinus]

{{Taxonbar|from1=Q15856|from2=Q15017992}}
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[[Category:Amphibians of Europe]]
[[Category:Amphibians described in 1768]]
[[Category:Cave salamanders]]
[[Category:Electroreceptive animals]]
[[Category:Fauna of Bosnia and Herzegovina]]
[[Category:Fauna of Croatia]]
[[Category:Fauna of Slovenia]]
[[Category:Oligotrophs]]
[[Category:Postojna Cave]]
[[Category:Proteidae]]
[[Category:Taxa named by Josephus Nicolaus Laurenti]]
[[Category:Habitats Directive species]]