Booms and busts among Europe’s insect populations are largely determined by the weather, according to a study of insect numbers in Germany. The finding could bring clarity to debates about what has caused the alarming decline of insect populations on the continent, but not all researchers are convinced.
“For now, this result is almost too good to be true,” says Hans de Kroon at Radboud University in the Netherlands, who wasn’t involved with the new study. “It’s a pretty strong claim.”
Much of the alarm regarding Europe’s insects dates to a 2017 study by de Kroon and his colleagues that found a shocking 76 per cent decline in flying insect biomass in protected areas in Germany between 1989 and 2016. That and other findings led to warnings of a global “insect apocalypse” and widespread insect extinctions. While those claims may have been overblown, insects are clearly in trouble – one analysis found terrestrial insect biomass in sites around the world has decreased by around 11 per cent each decade since the 1980s.
Jörg Müller at the University of Würzburg in Germany says that, like many of his colleagues, he initially thought the decline was down to a loss of insect habitats due to agriculture and urbanisation. But his research found that insect biomass didn’t change much between agricultural and more natural environments. “The decline was everywhere,” he says.
That suggested to him that the process was being driven by something that affects landscapes over larger scales, such as the weather. An unexpected rise in insect biomass at some trapping sites since 2016 – as well as a surfeit of butterflies around his house this year – also suggested a more fickle driver than changes in the landscape.
Using data on insect biomass from the 2017 study as well as from more recent trappings across southern Germany up to 2022, Müller and his colleagues tested seven different statistical models linking changes in insect biomass with a different set of variables, from changes in habitat to the weather.
They found the models that took weather into account could explain more of the observed patterns in insect biomass than the models that didn’t consider weather. They also found they could predict changes in insect biomass at sites elsewhere in Germany using weather variables alone.
This link with weather suggests a mechanism through which climate change may be affecting insect populations. A warmer, drier winter, for instance, seems to have a negative influence on biomass, while a warmer, wetter spring has a positive influence. Europe has seen both warmer winters and springs with climate change. However, Müller says the relationship is too complex to yet say precisely how climate change is playing a role. “It’s definitely risky, and it’s getting more risky for insects,” he says, particularly the rare or threatened ones.
For his part, de Koon says he has yet to “look under the hood” of the modelling, but finds it difficult to believe weather can explain the dramatic decline, especially across so many species of insect. “It’s hard to imagine that the group as a whole responds uniformly to those very specific weather anomalies,” he says.
He is also sceptical of the reported rise in insect biomass since 2016, pointing to recent data that describes continued decline. “We don’t see any accounts for the time being for a recovery in the insect community,” he says.