Common blue butterfly
(Polyommatus icarus)
Photo: Gerlind Lehmannn

The insect population in German nature reserves has been declining for decades. A study conducted by the University of Würzburg in 2023 identified weather conditions as the main cause of insect mortality. Poor weather conditions would lead to a decline in insect populations, while good weather would cause a recovery. A recent study published in the scientific journal Nature now refutes the findings of the Würzburg study.

The authors, led by Prof Dr Hans de Kroon from Radboud University in Nijmwegen and in collaboration with Prof Dr Gerlind Lehmann from Humboldt-Universität zu Berlin (HU), among others, found that weather conditions are not the main cause of insect mortality and do not lead to short-term recoveries in insect biomass. They show that the study by the University of Würzburg cannot stand up to scientific scrutiny, as it has significant flaws in the chosen models, methodologies and locations. For example, the scientists took samples from artificially created forest niches in which more insects naturally occur than in other habitats. According to the authors in Nature, this does not indicate that the insect population has recovered overall.

Researching insect extinction and protecting biodiversity

A 2017 study estimated the extent of insect mortality in Germany at 76 per cent over the course of 28 years. The Nature authors confirm the ongoing decline in populations. "Depending on the data set, insect populations in German nature reserves either show no recovery or even a further decline," says HU Professor Gerlind Lehmann. As scientific coordinator of the project "Diversity of Insects in Nature  protected Areas" (DINA), she is investigating insect diversity in nature reserves. By analysing the reasons for the decline in insects, it is possible to take action and protect biodiversity: "The latest results once again underline the importance of current research to identify the main drivers of insect extinction and develop viable solutions to protect biodiversity," says Lehmann.

In Nature, the researchers welcome approaches to further investigate the influence of weather anomalies under climate change as a cause of insect mortality. 

Further information

Study: Hallmann C.A., Jongejans E., Hörren T., Sorg M., Siepel H., Mühlethaler R., Lehmann G.U.C., de Kroon H.: Weather anomalies cannot explain insect decline, Nature, 13.03.2025, doi.org/10.1038/s41586-024-08528-0

Link to the study