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Biospeleology Research Centre

phone: (+359 2) 9885115 (ext. 678)

Biospeleology studies the organisms that live in caves and other subterranean environments. The National Museum of Natural History in Sofia is the only research institution involved in the long-term systematic exploration and cataloguing of the Bulgarian cave fauna.

Brief history of the biospeleological studies in Bulgaria

The first to find cave animals in Bulgaria was the Hungarian entomologist Eduard Merkl. In 1878 he visited some caves near the summits Kurudza and Sveti Nikola (now Stoletov) in Central Stara Planina Mountain. There, Merkl discovered three blind beetles which were described by the Hungarian entomologists Johan Frivaldzsky in 1879 as Trechus (Anophthalmus) balcanicus, Pholeuon merkli, and Ph. merkli var. simile. This discovery remained largely unknown for a long time as it was not mentioned in the descriptions that the beetles were found in caves.

The systematic exploration of Bulgarian caves began in 1922. Many caves in different regions were explored by the then director of the Royal Museum of Natural History Dr Ivan Buresch and his collaborators Neno Atanasov, Pencho Drenski and Nenko Radev. Only between 1923 and 1926 tens of new troglobite species were discovered and described. First review papers on the cave-dwelling fauna of the country were published by Buresch in 1926, 1928 and 1936. The second wave of intensive cave research activities in Bulgaria started in 1958. A new generation of biospeleologists (P. Beron, V. Guéorguiev, Ch. Deltshev, V. Beshkov, T. Michev, M. Kwartirnikov, A. Popov, St. Andreev) initiated field surveys in hundreds of caves. The first detailed review of the Bulgarian cave fauna was published by V. Guéorguiev and P. Beron in 1962. Subsequent additions were published by Beron and Guéorguiev in 1967 and Beron, in 1973 and 1994.

Since 1995, a third generation of Bulgarian biospeleogists — P. Stoev, I. Pandurski, B. Guéorguiev, T. Ivanova, N. Simov, B. Petrov has continued the exploration of Bulgarian caves with new inspiration and knowledge. Tens of new terrestrial and aquatic taxa were collected and described. The first systematic investigation of the Mesocavernous Shallow Stratum (MSS) in Bulgaria and its fauna began in 2005. At present, a complete review of all hitherto known subterranean organisms in Bulgarian caves entitled ‘The cave fauna of Bulgaria’ is in preparation by experts from the Biospeleology Research Centre.

Cave fauna of Bulgaria

Animals that are adapted to living in complete darkness and with limited energy supplies usually acquire a specific appearance that includes depigmentation, micro- or anophthalmy, loss of wings, elaboration of extra-optic sensory structures, elongation of appendages (in cases of troglobionts) or shortening of appendages (in case of geobionts), cuticle thinning, etc. These morphological alterations known as troglomorphy are widespread in subterranean animals.

Quick facts:

Animals are known from more than 780 caves.
800 species of animals have hitherto been recorded from Bulgarian caves.
160 species are considered strict cave-dwellers (troglobites and stygobites).
More than 440 biospleological papers were published.
New taxa of animals are discovered or described every year.
The fauna of 5200 caves remains unstudied.

By the end of 2010, over 800 animal species have been recorded from Bulgarian caves. Among them, more than 160 species are considered troglobites. The species richest in troglobites groups are the ground beetles (genera Pheggomisetes, Duvalius, Rambousekiella), leptodirini (genera Bathyscia, Beronia, Beskovia, Hexaurus, Netolitzkya, Radevia, Rhodopiola, Tranteviella, Bureschiana, Genestiellina, Balcanobius, Beroniella, Vratzaniola), millipedes (genera Typhloiulus, Serboiulus, Apfelbeckiella, Rhodopiella, Balkanopetalum, Troglodicus, Rhodoposoma, Bulgarosoma, Bulgardicus, Anamastigona, Stygiosoma, Polydesmus, Bacillidesmus, Trachysphaera, Lithobius and Eupolybothrus) and isopods (genera Trichoniscus, Bulgaronethes, Beroniscus, Cordioniscus, Hyloniscus, Bulgaroniscus, Balkanoniscus, Vandeloniscellus, Tricyphoniscus, Bureschia, Rhodopioniscus). Less rich in troglobites are the spiders (genera Protoleptoneta, Centromerus, Troglohyphantes, Porrhomma, Nesticus), harvestmen (genera Tranteeva, Paralola, Siro, Paranemastoma) and pseudoscorpions (genera Balkanoroncus, Neobisium, Roncus, Chthonius). No strict cave-dwellers are known among the vertebrate animals.

List of the higher taxa of invertebrates found in Bulgarian caves

GroupNumber of speciesTroglobites
Copepoda5826 (45%)
Isopoda5430 (55%)
Pseudoscorpiones157 (47%)
Opiliones194 (21%)
Araneae805 (6%)
Diplopoda5417 (31%)
Chilopoda285 (18%)
Collembola417 (17%)
Coleoptera11936 (30%)

List of higher taxa of vertebrates found in Bulgarian caves


Protection of the cave-dwelling fauna in Bulgaria

None of the invertebrate species found in the caves of Bulgaria is legally protected by the National Biodiversity Act. However, after the Habitat Directive 92/43/EEC all caves, which are not open to the public are formally declared as sites of conservation importance.

Types of caves in Bulgaria after the Classification of Palaearctic habitats

12.72Complex sea caves
65.22Continental bat caves
65.41Troglobiont invertebrate temperate caves
65.42Troglobiont invertebrate ice caves
65.5Troglophile invertebrate caves
88Mines and underground passages

Types of caves in Bulgaria after the Habitat Classification of NATURA 2000

8310Caves not open to the public
8330Submerged or partially submerged sea caves

Recommendation No 36/1992 on the Conservation of underground habitats adopted by the Standing Committee under the terms of Article 14 of the Convention on the Conservation of European Wildlife and Natural Habitats formulates the basic advices for protection, exploration and management of the underground habitats.

Biospeleology Research Centre’s team

Assoc. Prof. Dr Petar Beron
Assoc. Prof. Dr Pavel Stoev
Assoc. Prof. Dr Stoyan Lazarov
Assoc. Prof. Dr Borislav Guéorguiev
MSc Boyan Petrov
Dr Nikolay Simov

Selected literature

Beron P. 1972. Essai sur la faune cavernicole de Bulgarie. III. Résultats des recherches biospéologiques de 1966 à 1970. — Int. J. Speleol., 4: 285—349. [PDF]

Beron P. 1994. Résultats des recherches biospéléologiques en Bulgarie de 1971 à 1994 et liste des animaux cavernicoles bulgares. — Tranteeva, Sofia, 1: 1—137.

Beron P. 2007. Terrestrial Cave Animals in Bulgaria. — In: V. Fet & A. Popov (eds.) Biogeography and Ecology of Bulgaria, Springer, 493—526. [PDF]

Beron P., Guéorguiev V. 1967. Essai sur la faune cavernicole de Bulgarie. II. Résultats des recherches biospéléologiques de 1961 à 1965. — Bull. Inst. Zool. Mus., 24: 151—212.

Beron P., Petrov B., Stoev P. 2004. The invertebrate cave fauna of the Eastern Rhodopes (Bulgaria and Greece). — In: Beron P. & Popov A. (eds). Biodiversity of Bulgaria. 2. Biodiversity of Eastern Rhodopes (Bulgaria and Greece). Pensoft & Nat. Mus. Natur. Hist., Sofia, 791—822. [PDF]

Beron P., B. Petrov, P. Stoev. 2011. Invertebrate cave fauna of the Western Rhodopes (Bulgaria and Greece). — In: P. Beron (ed.). Biodiversity of Bulgaria, 4. Biodiversity of Western Rhodopes (Bulgaria and Greece). Pensoft & Nat. Mus. Natur. Hist., Sofia, 583—661. [PDF].

Guéorguiev V. 1977. La faune troglobie terrestre de la péninsule Balkanique. Origine, formation et zoogéographie. Ed. Acad. bulg. Sci., Sofia, 182 pp.

Guéorguiev V., Beron P. 1962. Essai sur la faune cavernicole de Bulgarie. — Ann. de Spéléologie; 17 (2—3): 285—441.

Pandrurski I. 2007. Stygofauna of the Fresh Waters in Bulgaria. — In: V. Fet & A. Popov (eds.), Biogeography and Ecology of Bulgaria, Springer, 527—536. [PDF]

Stoev P. 2001. A synopsis of the Bulgarian cave centipedes (Chilopoda). — Arthropoda Selecta, 10 (1): 31—54.

Stoev P. 2004. New distributional records of millipedes from Bulgarian caves (Myriapoda: Diplopoda). — Acta zoologica bulgarica, 56 (2): 145—154. [PDF]


The Caves of Bulgaria [in Bulgarian]