Shawan Chowdhury , Diana E. Bowler, Estève Boutaud, Ortwin Bleich, Helge Bruelheide, Jörn Buse, Thore Engel, Jörg Gebert, Volker Grescho, Stephan Gürlich, Ingmar Harry, Florian Jansen, Reinhard A Klenke, Roel van Klink, Marten Winter, Aletta Bonn

Many insect species are facing existential crises, primarily due to diverse human-induced activities. Most insect assessments, however, are based on short-term data or some iconic species. Here, in close collaboration with taxonomic experts from natural history societies, we compiled the best available occurrence data for ground beetles in Germany, estimated the changes in species occupancy over the last 36 years, and related these changes to the traits/characteristics of these species. We obtained trends for 383 species and found that 52% of species significantly declined, and 22% significantly increased in site occupancy. The remainder of the species (26%) all showed a mean negative trend, albeit nonsignificant. Interestingly, non-threatened species declined at a similar rate to the threatened species, with 64% of the Near Threatened species experiencing significant declines (highest among all red list categories). Across all traits, we found that large (compared to medium) and omnivore (compared to predator) species declined less. Considering that ground beetles are key predators in many ecosystems and in agricultural systems that play an important role in pest control and in the food chain, their decline should raise concerns. Thus, we urgently plead for more harmonised and systematic monitoring of this insect group.