Evidence of population stress linked to droughts in cave-dwelling spiders: the case of Meta bourneti in north-western Italy

Subterranean spiders of the genus Meta are frequent inhabitants of the twilight zones of European caves, where they play a key ecological role as apical predators. We assessed the abundance variation and breeding success of M. bourneti populations after an extensive drought period that affected north-western Italy during 2022. Across three different caves, we compared data with the results of a previous monitoring study performed in 2012–2013 in the same sites, which are at the gedge of the species’ range in the Italian peninsula. From December 2022 to December 2023, we carried out three surveys in spring and winter seasons. We detected a total of 20 M. bourneti individuals, while more than 100 individuals were reported in 2012–2013. Moreover, we did not observe any cocoons. The observed decline and absence of breeding may reflect cyclic or stochastic population fluctuations, but it is worth noting that an extensive drought occurred during the period 2021–2022. We emphasize the importance of establishing long-term monitoring of M. bourneti populations in Mediterranean regions to improve our understanding of the potential effects of climate change in subterranean ecosystems.