Researchers find 'alarming' loss of insects in large-scale study in Germany

November 5, 2019, 3:25 p.m.

Insects are in more trouble than we thought.

A large-scale study has found that insects in German forests and grasslands have declined by about one-third in just the past decade. That follows on the heels of a 27-year study that also showed declines.

"A decline on that scale over a period of just 10 years came as a complete surprise to us," says Wolfgang Weisser, professor of terrestrial ecology at Technical University of Munich, in a statement. "It is frightening, but fits the picture presented in a growing number of studies."

The researchers collected more than 1 million insects at 300 sites between 2008 and 2017. Of the nearly 2,700 species they investigated, they found that many are in decline. They were unable to find some species at all.

In forests and grasslands, they counted about 34% fewer insect species. The abundance of insects dropped 78% and the total weight, or biomass, dropped 67%. Their results were published in the journal Nature.

Researchers found that the major drivers behind the decline were related to farming practices. The greatest losses were in grasslands surrounded by areas that were intensively farmed, particularly where the most impacted species were unable to travel very far.

In forested areas, however, the insects that were most affected were those that cover long distances.

"Our study confirms that insect decline is real — it might be even more widespread then previously thought considering, for example, that also forests are experiencing declines in insect populations," Sebastian Seibold of the Technical University of Munich told BBC News.

"I think it's alarming to see that such a decline happens not only in intensively-managed areas but also in protected areas — so the sites that we think are safeguarding our biodiversity are not really working anymore."

Ecosystems are resilient, but it's time to act

In recent years, other studies have found that insects have been disappearing, but they typically only focused on biomass and not species.

For example, another study in Germany was conducted over the course of 27 years. Researchers set up a series of malaise traps — tents that catch and funnel flying insects into bottles of alcohol — across 63 nature protection areas. Typically, such traps are used for general education purposes, but as the years went on, the team noticed they were collecting fewer and fewer insects. So much so that between 1989 and 2016, the biomass of the insects collected fell by 77% between May and October.

The insects in the study included butterflies, bees and and moths, and the insects were collected from a range of habitats around Germany. The study notes that the findings are especially alarming since those habitats are in "protected areas that are meant to preserve ecosystem functions and biodiversity."

The results were published in the journal PLOS One.

Insects are a vital part of our food web, from being a source of food for birds to being pollinators for our crops. As insects decline, so do their ecosystems, and that has a ripple effect that reaches every organism on the planet.

That being said, as the Atlantic points out in its report on the study, if insects in Germany have disappeared as much as they have, why hasn't there been similar declines in flowers, birds, reptiles and the like?

"Some species could switch food sources, but we don't really know what's going on. We do know that we see declines in even common species, like blackbirds, starlings and sparrows," Hans de Kroon, who analyzed the study's data, explained to the Atlantic.

But it's also possible, as de Kroon noted, that the environments are just adapting the best they can to the population loss.

"We don't want people to get depressed," de Kroon said. "Ecosystems are very resilient. They're still functioning quite well despite this loss. Let's make use of that resilience. We can't wait till we know exactly what's leading to these losses. We have to act."

Editor's note: This story has been updated with new information since it was originally published in October 2017.