The olm or proteus (Proteus anguinus ) is an aquatic salamander in the family Proteidae, the only exclusively cave-dwelling chordate species found in Europe. In contrast to most amphibians, it is entirely 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 and Southeastern Europe in the basin of the Soča River (Italian: Isonzo) near Trieste, Italy, southwestern Croatia, and Bosnia and Herzegovina. Introduced populations are found near Vicenza, Italy, and Kranj, Slovenia.
It is also called the "human fish" by locals because of its fleshy skin color (translated literally from Slovene: človeška ribica, Macedonian: човечка рипка, Croatian: čovječja ribica, Bosnian: čovječja ribica Serbian: човечја рибица), as well as "cave salamander" or "white salamander". In Slovenia, it is called močeril (from *močerъ 'earthworm, damp creepy-crawly'; moča 'dampness'). It was first mentioned in 1689 by the local naturalist Valvasor in his 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 eyes are undeveloped, leaving it blind, while its other senses, particularly those of smell and hearing, are acutely developed. It also lacks any pigmentation in its skin. It has three toes on its forelimbs, but only two toes on its hind feet. It exhibits neoteny, retaining larval characteristics like external gills into adulthood, like some American amphibians, the axolotl and the mudpuppies (Necturus ). The olm is the only species in the genus Proteus and the only European species of the family Proteidae, whose other extant genus is Necturus.
The word olm is a German loanword that was incorporated into English in the late 19th century. The origin of the German original, Olm or Grottenolm 'cave olm', is unclear. It may be a variant of the word Molch 'salamander'.
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CarnivoreA carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of a...
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InsectivoresAn insectivore is a carnivorous plant or animal that eats insects. An alternative term is entomophage, which also refers to the human practice of e...
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NatatorialNatatorial animals are those adapted for swimming. Some fish use their pectoral fins as the primary means of locomotion, sometimes termed labriform...
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TerritorialA territory is a sociographical area that which an animal consistently defends against the conspecific competition (or, occasionally, against anima...
Oviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
Among animals, viviparity is the development of the embryo inside the body of the parent. The term 'viviparity' and its adjective form 'viviparous'...
Precocial species are those in which the young are relatively mature and mobile from the moment of birth or hatching. Precocial species are normall...
A fossorial animal is one adapted to digging which lives primarily but not solely, underground. Some examples are badgers, naked mole-rats, clams, ...
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PolygynyPolygyny is a mating system in which one male lives and mates with multiple females but each female only mates with a single male.
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PolygamyPolygamy is the practice of breeding with multiple partners. When a male breeds with more than one female at the same time – it is called polygyny....
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Not a migrantAnimals that do not make seasonal movements and stay in their native home ranges all year round are called not migrants or residents.
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starts withThe olm's body is snakelike, 20–30 cm (8–12 in) long, with some specimens reaching up to 40 centimetres (16 in). The average length is between 23-25 cm. Females grow larger than males, but otherwise the primary external difference between the sexes is in the cloaca region (shape and size) when breeding. 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 pigment riboflavin, making it yellowish-white or pink in color.
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 larvae are also colored. Its pear-shaped head ends with a short, dorsoventrally flattened snout. The mouth opening is small, with tiny teeth forming a sieve to keep larger particles inside the mouth. The nostrils are so small as to be imperceptible, but are placed somewhat laterally near the end of the snout. The regressed eyes are covered by a layer of skin. The olm breathes with external gills that form two branched tufts at the back of the head. They are red in color because the oxygen-rich blood shows through the non-pigmented skin. The olm also has rudimentary lungs, but their role in respiration is only accessory, except during hypoxic conditions.
The olm lives in well-oxygenated underground waters with a typical, very stable temperature of 8–11 °C (46–52 °F), infrequently as warm as 14 °C (57 °F). The black olm may occur in surface waters that are somewhat warmer.
At a temperature of 10 °C (50 °F), the olm's embryonic 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 15 °C (59 °F). After hatching, it takes another 14 years to reach sexual maturity if living in water that is 10 °C (50 °F). The larvae gain adult appearance after nearly four months, with the duration of development strongly correlating with water temperature. 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. Paul Kammerer reported that female olm gave birth to live young in water at or below 13 °C (55 °F) and laid eggs at higher, but rigorous observations have not confirmed that. The olm appears to be exclusively oviparous.
The female lays up to 70 eggs, each about 12 millimetres (0.5 in) in diameter, and places them between rocks, where they remain under her protection. The average is 35 eggs and the adult female typically breeds every 12.5 years. The tadpoles are 2 centimetres (0.8 in) long when they hatch and live on yolk stored in the cells of the digestive tract for a month.
Development of the olm and other troglobite amphibians is characterized by heterochrony – the animal does not undergo metamorphosis and instead retains larval features. The form of heterochrony in the olm is neoteny – delayed somatic maturity with precocious reproductive maturity, i.e. reproductive maturity is reached while retaining the larval external 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 tissues to thyroxine.
The olm swims by eel-like twisting of its body, assisted only slightly by its poorly developed legs. It is a predatory animal, feeding on small crustaceans (for example, Troglocaris shrimp), snails and occasionally insects. 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 lipids and glycogen in the liver. When food is scarce, it reduces its activity and 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.
Olms are gregarious, and usually aggregate either under stones or in fissures. 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. This is a behavioral adaptation to life underground.
Reproduction has only been observed in captivity so far. 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.
Longevity is estimated at up to 58 years. 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 outliers, living longer than would be predicted from their size.
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. 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.
Among the most serious chemical pollutants are chlorinated hydrocarbon pesticides, fertilizers, 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.
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 areas 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. Postojna Cave and other caves inhabited by the olm were eventually included in the Slovenian part of the Natura 2000 network. Capturing or killing olm is allowed only under specific circumstances determined by the local authorities (i.e. scientific study).
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 Slovenian Red list of endangered species.
In Croatia, the olm is protected by the legislation designed to protect amphibians – collecting is possible only for research purposes by permission of the National Administration for Nature and Environment Protection. As of 2020 the Croatian population has been assessed as 'critically endangered' in Croatia. As of 1999, the environmental laws in Bosnia and Herzegovina and Montenegro had not yet been clarified for this species.
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 all subsequent assessments. Since the 1980s until the most recent assessment in 2008 the organisation has rated the conservation status for the IUCN Red List as '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.
Zagreb Zoo is a zoo in Croatia that houses the olm. Olms were until recently formerly kept in numerous zoos in Germany, as well as in the UK, Belgium and Slovenia. At present they can only be experienced at Zagreb Zoo, Hermannshöhle in Germany and Vivarium Proteus (Proteus Vivarium) within Postojnska jama (Postojna Cave) in Slovenia. There are also captive breeding programs in France and Germany.
Social animals are those animals that interact highly with other animals, usually of their own species (conspecifics), to the point of having a rec...