Spiders newly observed in Czechia in recent years – overlooked or invasive species?

To learn whether the recent increase in the number of Central European spider species reflects a still-incomplete state of faunistic research or real temporal changes in the Central European fauna, we evaluated the records of 47 new species observed in 2008–2020 in Czechia, one of the faunistically best researched regions in Europe. Because of the intensified transportation of materials, enabling the introduction of alien species, and perhaps also because of climatic changes that allow thermophilic species to expand northward, the spider fauna of this region is dynamic. Our analysis showed that only 15 spider species newly recorded in Czechia likely belong to the indigenous fauna. The remaining two-thirds likely appeared in this region recently. Half of these species are likely thermophilic species that expanded their distribution to the north, possibly due to global warming, and the second half are subtropical or tropical species introduced to heated buildings. Only three species were introduced to natural habitats, and only two of them, Mermessus trilobatus and Erigone autumnalis (Linyphiidae), can be considered true invasive species.