The decline in insects and spiders in Germany goes further than previously thought. Since 2009, about a third of all species have disappeared from meadows and forests. The result is a study by the Technical University of Munich (TUM), published today in the journal Nature (Seibold et al., 2019).
"Previous studies either focused exclusively on biomass, that is, the total weight of all insects, or on individual species or species groups," says lead author Sebastian Seibold, an ecologist at TUM's Department of Terrestrial Ecology. "That actually affects a large part of all insect groups, was not yet clear."
Beginning in 2009, the scientists examined how the population of insects and spiders in three regions of Germany has changed - in areas in the Swabian Alb, in the Hainich National Park and in the Schorfheide Chorin. Not only did they examine protected areas, but also forests and meadows that are either used moderately as arable land or grazing land for sheep and cattle, or that are intensively farmed by humans - with regular fertilization, for example. Overall, the evaluation showed that both the number of insect species and the biomass decreased massively - in the meadows alone by more than two-thirds. "This shows that the problem goes further than we previously thought," says Axel Hochkirch from the Center for the Protection of Biodiversity at the University of Trier.
The most surprised was the biologist, who himself was not involved in the study, but of the decline in the forests. There, the biomass shrank by 41 percent. The forest was in contrast to arable land and meadows so far as a kind of shelter for insects and spiders. Especially since forest owners and foresters have been relying on sustainable farming for some time now: monkey-farming monocultures and leaving deadwood often behind them. "We had the impression that the problems there are not as obvious as in the open countryside," says Hochkirch.
More and more signs of insect shrinkage
Why the arthropods disappear so strongly in the forest, the scientists could not yet explain sufficiently. In particular, there has been a decline in such insects that travel long distances. Whether it suggests that bees, beetles and butterflies get problems when they come into contact with agriculture, or whether the cause can not be found in the forests themselves, the study can not explain.
Already in 2017, a survey of the entomological association Krefeld revealed a loss of flying insects in 63 German protected areas. Over 27 years, the entomologists had taken samples of beetles, bees and butterflies, especially in North Rhine-Westphalia. The ecologist Caspar Hallmann from the Radboud University Nimwege has evaluated the data: Over three quarters had shrunk in the period, the collected insect mass. The study (Hallmann2017) has made public for the first time that large numbers of insects disappear from Germany, and initiated a series of political initiatives. For example, since August 1, a law on the protection of species in Bavaria has stipulated that the proportion of organic agriculture should more than triple and the use of pesticides should be limited.