Ed Yong in The Atlantic:
Since 1989, scientists from the Entomological Society Krefeld had been collecting insects in the nature reserves and protected areas of western Germany. They set up malaise traps—large tents that funnel any incoming insect upward through a cone of fabric and into a bottle of alcohol. These traps are used by entomologists to collect specimens of local insects, for research or education. “But over the years, [the Krefeld team] realized that the bottles were getting emptier and emptier,” says Caspar Hallmann, from Radboud University.
By analyzing the Krefeld data—1,503 traps, and 27 years of work—Hallmann and his colleagues have shown that most of the flying insects in this part of Germany are flying no more. Between 1989 and 2016, the average weight of insects that were caught between May and October fell by an astonishing 77 percent. Over the same period, the weight of insects caught in the height of summer, when these creatures should be at their buzziest, fell by 82 percent.
More here.