NATURA SLOVENIAE 19(2): 55-61 Prejeto / Received: 16.10.2017 
SHORT COMMUNICATION Sprejeto / Accepted: 7.12.2017 
Biotehniška fakulteta Univerze v Ljubljani in Nacionalni inštitut za biologijo, Ljubljana, 2017 
 
 
 
First record of a specialized hygropetricolous cave 
beetle, genus Croatodirus (Coleoptera: Leiodidae), in 
Slovenia 
 
 
 
Teo DELIĆ 
 
 
Department of Biology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia;  
E-mail: teo.delic@bf.uni-lj.si 
 
 
 
Abstract. The cave hygropetric, an inaccessible subterranean habitat defined by films of water flowing down 
the cave walls, is renowned for its specialized filter feeding cave beetles. To date, no data on cave 
hygropetricolous beetles have been known for Slovenia, despite the existence of suitable karst areas. This paper 
reports on the first finding of a hygropetricolous cave beetle in Slovenia. A single female of a species belonging to 
the genus Croatodirus was discovered in the cave »Brezno treh src« on the Snežnik Plateau. The geomorphology 
and climate of the sampling site as well as the biology of hygropetricolous cave beetles are briefly described. 
 
Key words: hygropetricolous beetles, cave hygropetric, Croatodirus, Mt Snežnik, Brezno treh src, Dinaric Karst, 
troglobiont 
 
 
Izvleček. Prva najdba specializiranega hrošča iz rodu Croatodirus (Coleoptera: Leiodidae) v 
jamskem higropetriku v Sloveniji – Težko dostopne podzemeljske habitate, katerih značilnost je čez stene v 
obliki filma mezeča voda, imenujemo jamski higropetrik. Ta je znan po jamskih hroščih, ki se prehranjujejo s 
filtriranjem vode. Doslej o pojavljanju specializiranih higropetričnih hroščev, kljub obstoju primernih območij, v 
Sloveniji ni bilo podatkov. V prispevku je podan opis prve najdbe higropetričnega hrošča iz rodu Croatodirus za 
Slovenijo, iz »Brezna treh src« na Snežniku. Opisani so tudi geomorfologija, klimatske lastnosti najdišča ter kratek 
pregled biologije higropetričnih hroščev. 
 
Ključne besede: higropetrični hrošči, jamski higropetrik, Croatodirus, Snežnik, Brezno treh src, Dinarski kras, 
troglobiont 
 
 
 
Introduction  
 
In their study, Giachino & Vailati (2006) stated that specialized hygropetricolous beetles 
(referred to also as hygropetric) are bound to geographical areas receiving more than  
2000 mm total annual precipitation. This conclusion was based on the overview of the 
localities where hygropetricolous beetles were known to exist (Fig. 1). The areas exceeding 
this limit were hypothesized to enable the functioning of a special subterranean habitat, the 
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NATURA SLOVENIAE 19(2): 55-61 
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cave hygropetric (Sket 2004, Giachino & Vailati 2006). Defined by a constant influx of 
percolating waters derived from the surface, the cave hygropetric enables the formation of 
rich microbial communities that serve as nutrients to hygropetricolous beetles (Engel et al. 
2013, Paoletti et al. 2013). 
 
 
Figure 1. Distribution of the hygropetricolous beetles from the genus Croatodirus. The areas exceeding 2,000 mm 
annual precipitation, enabling existence of the cave hygropetric, are indicated in light blue = 2,000 to 2,500 mm, dark 
blue = 2,500 to 3,000 mm, violet = 3,000 to 3,500 mm and purple = 3,500 to 4,000 mm annual precipitation. Data 
sources: Subbio Database (www.subbio.net/db), ESRI World Imagery (www.esri.com), Ranković et al. 1961. 
Slika 1. Razširjenost higropetričnih hroščev iz rodu Croatodirus. Označena so območja z več kot 2000 mm letne količine 
padavin, meje, ki omogoča obstoj jamskega higropetrika (svetlo modra = 2000 do 2500 mm, temno modra = 2500 do 
3000 mm, svetlo vijolična = 3000 do 3500 mm in temno vijolična 3500 do 4000 mm letne količine padavin). Viri: 
podatkovna baza Subbio Database (www.subbio.net/db), ESRI World Imagery (www.esri.com), Ranković et al. 1961. 
 
All known genera of hygropetricolous beetles, i. e. the Dinaric genera Hadesia Müller 1911, 
Radziella Casale & Jalžić 1988, Tartariella Nonveiller & Pavićević 1999, Croatodirus Casale, 
Giachino & Jalžić 2000, Nauticiella Moravec & Mlejnek 2002, Velebitodromus Casale, Giachino 
& Jalžić 2004 and Kircheria Giachino & Vailati 2006, as well as the sole Alpine genus Cansiliella 
Paoletti 1972, share similar morphological adaptations (Perreau & Pavićević 2008). The most 
conspicuous include a highly hydrophobic pubescence of exoskeleton, an elongated and 
specifically shaped head, increased size of mandibles and feeding apparatus, densely covered 
with thickened filtering setae, and specialized claws that enable them holding on to the 
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surface despite strong water current (Moldovan et al. 2004, Giachino & Vailati 2006,  
Perreau & Pavićević 2008). Phylogenetic relations among these genera have not been 
disentangled up to date, but preliminary data suggest that adaptations to hygropetric habitats 
evolved convergently in some of the distantly related genera (Polak et al. 2016). 
 
Throughout the Dinaric Karst, several regions with high level of precipitation and 
harbouring highly endemic hygropetricolous beetles were recognized (Giachino & Vailati 2006, 
2010). These areas include mountain plateaus and ridges along the eastern Adriatic coast and 
in the inner Dinarides – Gorski kotar, Učka, Velebit, Biokovo, Lovćen, Durmitor and Prokletije – 
all renowned for their rich endemic obligate subterranean fauna. The arc of high-precipitation 
limestone massifs in the hinterland of the Adriatic Sea extends all the way to the Italian 
Prealps where hygropetricolous cave beetles are represented by the genus Cansiliella. 
Although karst areas with high annual precipitation, exceeding 2000 mm yearly, are present in 
the northern most part of the Dinaric Karst (Ranković 1961), no hygropetricolous beetles have 
been found here to date. Such are the high karst plateaus of Trnovski gozd and Snežnik  
(Fig. 1). Both areas were thoroughly explored in a speleological and speleobiological sense in 
the past. Moreover, with 11 troglobiotic beetles, the cave Ledenica v Dolu on the Trnovski 
gozd massif represents the richest locality for subterranean beetles in the world (Bognolo 
2002, Zagmajster 2007). Despite recent thorough sampling efforts in caves with permanent 
water flow in the vadose zone of Trnovski gozd (Borko 2016) and Snežnik (own unpublished 
data), no specialized filter feeding beetles were found. Although areas with potentially suitable 
habitats had been recognized, Slovenia remained the only country throughout the Dinaric 
Karst with no records of hygropetricolous cave beetles. Nonetheless, the finding of such a 
cave animal has remained highly anticipated, as Slovenia represents the only large gap in the 
»hygropetricolous arc« spanning the carbonate range from Albania in the southeast to the 
Italian Prealps in the northwest. 
 
 
 
Results and discussion 
 
 
On Saturday, 9.9.2017, a hygropetricolous beetle from the genus Croatodirus was 
discovered in the cave Brezno treh src (B3S), Cifre, Mt Snežnik, Slovenia (Slovenian cave 
cadastre number 9834, DK – 48 x, y = 5460733, 5046077, WGS – 84 x, y = 14.4923°, 
45.5579°) (Fig. 2). A sole female Croatodirus beetle (Fig. 3) was found at the beginning of the 
cave hygropetric habitat at an approximate depth of 470 m, in a cave section referred to as 
Ljubljanska borza. It was found walking on a vertical wall, approximately 30 cm from the main 
water flow. The beetle was photographed in its natural habitat and instantly preserved in 96% 
ethanol. A representative of another troglobiotic beetle genus, Parapropus sericeus, was 
spotted nearby. Interestingly, the cave was visited and thoroughly inspected by the author 
eight times. Despite considerable observation effort, and probably due to the suboptimal 
habitat characteristics and low population density, this was the first time a hygropetricolous 
beetle was found in this or any other cave in Slovenia. Other specialized troglobiotic beetle 
fauna includes Anophthalmus spectabilis and Typhlotrechus bilimekii from the subfamily 
Trechinae (Carabidae), and Astagobius angustatus, Bathysciotes khevenhuelleri, Leptodirus 
hochenwartii, Parapropus sericeus and Spelaeodromus sneznikensis from the subfamily 
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Cholevinae (Leiodidae) (beetles are preserved in Zoological collection of the Department of 
Biology, Biotechnical Faculty, University of Ljubljana, Slovenia). 
 
Figure 2. Geographic position of the entrance to the cave Brezno treh src, marked with a red circle. Nearby caves are 
represented with brown dots (a). Section of the cave (modified from Vengar 2010), with the micro location of the 
Croatodirus find at an approximate depth of 470 m (b).  
Slika 2. Geografska lega vhoda v Brezno treh src, označena z rdečim krogom. Jame v okolici so označene z rjavimi 
točkami (a). Prerez jame (prilagojeno po Vengar 2010), z označenim mestom ulova osebka iz rodu Croatodirus, na 
približni globini 470 m (b).  
 
 
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Figure 3. A female of Croatodirus sp., the first hygropetricolous beetle observed in its natural habitat in Slovenia at a 
depth of 470 m in Brezno treh src, Cifre, Mt Snežnik (photo: T. Delić). 
Slika 3. Samica Croatodirus sp., prvi higropetrični hrošč, opažen v naravnem okolju v Sloveniji v Breznu treh src, Cifre, 
Snežnik, na globini 470 m (foto: T. Delić). 
 
The genus Croatodirus currently comprises three species: C. bozicevici Casale et al. 2000, 
C. casalei Giachino & Jalžić 2004, C. ozimeci Casale et al. 2004. The three species are 
narrowly endemic, each of them bound to a single massif of the Croatian Dinaric Karst; Učka, 
Velebit and Gorski kotar, respectively (Casale et al. 2004). All species are similar in 
appearance with only minute details enabling morphological identification of the species. While 
one of the species, C. ozimeci, is known from only one male specimen, the two other species, 
C. bozicevici and C. casalei, are known from relatively large populations from Mt Učka and 
Velebit, respectively (Casale et al. 2000, 2004). Like the other Croatodirus species, the beetle 
from Snežnik was also found in permanent water flows in the deeper sections of the vadose 
zone. Brezno treh src is more than 30 km apart from the nearest Croatodirus localities – 
Kaverna u tunelu Učka and Lokvarka (syn. Lokvarska špilja), type localities of C. bozicevici and 
C. ozimeci, respectively. Because of the limited dispersal within the subterranean realm and 
highly fragmented subterranean habitats of the Dinaric Karst (Trontelj et al. 2009, Konec et al. 
2016), we hypothesize that Croatodirus population from Mt Snežnik could belong to an 
independent lineage, possibly a separate species, despite the relatively small distance from 
the closest known Croatodirus sites. To test this hypothesis, DNA barcoding analysis or 
comparative morphological examination of additional specimens, especially males, are needed. 
 
Regardless of the outcome of these analyses, the discovery of a novel Croatodirus 
population is an important milestone for several reasons. First, the geographical range of the 
genus is extended further to the north and its maximal extent now exceeds 100 km (Velebit–
Snežnik). Second, Croatodirus speciation patterns seem to reflect the speciation patterns 
described in the southern Dinaric genus Hadesia (Polak et al. 2016). Likewise, the most recent 
common ancestral species probably inhabited the whole area where the genus is present 
nowadays, but aridification of the climate by the end of Miocene, and the ensuing glaciation 
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during the Pleistocene (Salzmann et al. 2011, Haywood et al. 2013), triggered vicariant 
speciation. Third, the discovery of a hygropetricolous cave beetle in Slovenia demonstrated 
that our knowledge of subterranean fauna is still scarce, despite the long tradition of 
speleobiology and years of targeted effort aimed at finding this particular type of beetles. 
 
 
 
Acknowledgements 
 
 
I would like to thank to all the participants who contributed to the exploration of the cave Brezno treh src, especially 
to members of the Society for cave exploration Ljubljana. In the first line I am grateful to Tomaž Šuštar, Slavko Polak, 
Andrea Colla and Špela Borko, who organized the exploration or helped with their fieldwork and identification. 
Additionally, I would like to thank Peter Trontelj and Maja Zagmajster for the help with rephrasing some parts of the text 
and to two anonymous reviewers for their helpful and constructive comments. 
 
 
 
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