Vertical distribution of spiders (Araneae) in Central European shallow subterranean habitats

Shallow subterranean habitats are among the last habitats in Central Europe to be arachnologically researched. Using stratified pipe traps, we studied the vertical distribution of spiders in soil and interspaces in bedrock (shallow subterranean habitats). Specifically, we sampled fauna in different substrates, including limestone, sandy marlstone, sandy marl, claystone, loess, and artificial gravel accumulation. Employing stratified pipe traps allowed us to identify the depth at which particular species occurred. Across multiple years and sampling sites, we collected 76 spider species, 21 of which showed an affinity for subterranean microhabitats. Some of these species occurred in interspaces in soil and bedrock, whereas others have been previously found in subterranean ant nests and animal burrows. We collected five species (Iberina microphthalma, Centromerus cf. piccolo, Porrhomma cambridgei, P. microcavense, and P. microps) almost exclusively at depths over half a meter, suggesting the strong affinity of these species for a subterranean lifestyle. We provide diagrams of these species' vertical distribution and photo-document eye reduction. Our study demonstrates that poorly studied shallow subterranean habitats harbor diverse subterranean spider fauna, including several previously considered rare species in Central Europe.