This study measuring the decline in flying insects, took place over 27 years in 63 nature protection areas in Germany. The researchers estimate that there has been “a seasonal decline of 76%, and mid-summer decline of 82% in flying insect biomass”.
The decline cannot though be pinned to one cause: It is “apparent regardless of habitat type . . . [C]hanges in weather, land use, and habitat characteristics cannot explain this overall decline.”
The researchers spell out a warning: “This yet unrecognized loss of insect biomass must be taken into account in evaluating declines in abundance of species depending on insects as a food source, and ecosystem functioning in the European landscape.”