Hallmann explained that the type of data provided by Malaise traps is bulky and hard to analyze at the species level.
“However,” he continued, “when you get an over 75 percent decline in total insect biomass, you know this is not due to a few or vulnerable species. This must be a decline in the entire spectrum of flying insects, from primary consumers like leaf-chewing bugs, all the way to parasitoid wasps and large bumble bees.”
The researchers chose to investigate flying insects in particular because, in Germany, out of the approximately 33,000 insect species that are present, over 90 percent are those that fly.
While no corresponding data over the same study period is available for non-flying insects, “we can just hope they are faring better, but we have no reason to believe that is the case,” Hallman said.
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Although Germany was selected as the location for the study, the findings likely apply to other countries. Many flying insect species travel long distances, going across country borders and even oceans.
The meticulous sampling of flying insects over so many sites and so many years yielded a dataset that is unique in the world, de Kroon told Seeker. In order to minimize the impact on flying insect communities, the team did not investigate each location annually.
“Therefore,” de Kroon continued, “we can only assess the overall decline over the study period, and are not able to look into the temporal variability in the rate of decline.”
He added that he and his team observed a decline in plant species richness locally in the vicinity of the traps, although that cannot yet be attributed to the decrease in numbers of insects. Prior research further shows insect-eating birds numbers have dramatically declined throughout Western Europe.
It then appears that plants, flying insects, and many birds — all of which have lives that are intertwined within their ecosystems — are decreasing in species diversity, if not in other respects.