The value of public databases for our knowledge of national spider biodiversity compared to a long‐term scientific monitoring project

Abstract Citizen science can be a valuable tool for monitoring changes in biodiversity, especially for less frequently studied taxonomic groups such as spiders. These collaborative projects between scientists and private citizens can provide a cost‐effective means of collecting large data sets, while also raising awareness of environmental and sustainability issues. A comparison of two public databases ( iNaturalist and the Swedish biodiversity database Artportalen ) with a national scientific study using malaise traps (Swedish Malaise Trap Project, SMTP) sheds light on their individual and combined contribution to our understanding of spider biodiversity and geographical distribution in Sweden. iNaturalist is an important global platform for mobilising public participation in biodiversity research. While widely used internationally, its coverage in Sweden is relatively limited and tends to over‐represent species that are easy to spot and often observed in densely populated areas. Artportalen includes a large body of observations contributed through citizen science. It offers wide species coverage, supported by higher expert input. Nevertheless, it exhibits sampling bias towards species that are diurnal and common in more populated areas. Projects based on large‐scale sampling schemes such as SMTP therefore make essential contributions to our understanding of the occurrence of species, especially for rare and uncommon species or species with cryptic life histories. Records are, however, limited in distribution to the pre‐defined sample locations. Given the more resource‐intensive nature of traditional scientific surveys, a combined approach that integrates citizen science data with scientific sampling offers the most robust and comprehensive means of assessing biodiversity.