In The Netherlands, the total biomass of flying insects has decreased by more than 75 percent in 63 nature reserves since 1989. In recent years, it became clear that the numbers of many types of insects such as butterflies and bees were declining in Western Europe and North America. “However, the fact that flying insects are decreasing at such a high rate in such a large area is an even more alarming discovery,” states Hans de Kroon, project leader at Radboud University.
Over the past 27 years, entomologists collected data in 63 different places within nature reserves across Germany. The data showed an average decline of 76 percent in the total insect mass. In the middle of summer, when insect numbers peak, the decline was more severe at 82 percent.
The causes of the decline are still unclear and not explained by changes in the weather, landscape and plant variety.