Insect decline also occurs in forests

Study of TU Darmstadt shows dramatic species decline

2023/06/18

The number of insects has been declining for years. This has already been well documented for agricultural areas. In forests, however, temporal trends are mostly studied for insect species that are considered pests. Now, a research team led by the Technical University Darmstadt have studied the trends of very many insect species in German forests. Contrary to what the researchers had suspected, the results showed: The majority of the studied species are declining. The results have been published in the scientific journal “Communications Biology”.

Picture: Christoph von Beeren

The green stink bug (Palomena prasina) is a common species that can be found on wooded areas in addition to forests. The animals are herbivores.
Picture: Philipp O. Hönle

The black-spotted longhorn beetle (Rhagium mordax) is a widespread and in some places common longhorn beetle in Central Europe. The larvae develop in dead wood. This species has declined in all three study regions.
Picture: Genevieve Walther

Study area in a beech forest in the Hainich National Park. Here, the insects have increased over the study period.
Picture: Nico Blüthgen

The trefoil spiny bug (Acanthosoma haemorrhoidale) is found mainly in deciduous forests, where it feeds on both leaf sap and fruit
Picture: Andrea Hilpert

The ant beetle (Thanasimus formicarius) is a predatory beneficial insect that feeds mainly on bark beetles. This species has declined in all three study regions.

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Forests in Central Europe have recently come to the public's attention due to their importance for climate mitigation and due to the omnipresent forest damage as a result of hot and dry summers. In addition to humans, many animal species depend on forest ecosystems, most of which are insects. Insects are often considered only as pests in the forest, as is shown, for example, by reports on bark beetles or cockchafers. While temporal changes in populations of potential insect pests are well studied, little is known about the status and trend of the many other fascinating insect species in forests.

A new study led by researchers from the Technical Universities of Darmstadt and Munich in collaboration with other researchers now shows how the populations of 1,805 insect species have developed in German forests from 2008 to 2017. To the researchers' surprise, the number of individuals has declined over time for the majority of the evaluated species.