For years, there has been talk of insect decline. People describe silent summer nights, clean windshields, and meadows where hardly anything is buzzing anymore. What was initially dismissed as a subjective impression has now been confirmed: several long-term studies show that insect biomass in Central Europe has declined sharply.
The so-called Krefeld Study (2017) became particularly well known. It documented a decline in the biomass of flying insects of more than 75% over 27 years – in German protected areas. Since then, there has been intense debate about why insects are disappearing. Central drivers include intensive agriculture, the use of pesticides, the loss and fragmentation of habitats, and climate change with increasing weather extremes.
A recent study published in the journal Nature Ecology & Evolution has now addressed a different, previously less considered question: What exactly is lost when insect biomass declines? Is it mainly fewer individuals that are counted, or are entire species disappearing from biological communities? The researchers therefore did not investigate why insects are declining, but how this loss manifests biologically.
Biomass as a key indicator
To assess the state of insect populations, scientists often rely on biomass. It describes the total living mass of all organisms in a given area – in other words, how much “insect life” is present overall. Biomass can be measured comparatively easily and is of central ecological importance: it forms the basis of food webs, drives energy flow through ecosystems, and influences numerous ecological processes. However, biomass alone does not reveal why it is declining or which species are affected.
This is exactly where the new study comes in. Over a period of eleven years, an international research team investigated arthropod communities in German grassland ecosystems. These included beetles, flies, true bugs, grasshoppers, and spiders, among others. Unlike many previous studies, the researchers did not only examine total biomass, but also analyzed species richness, individual densities, and the composition of communities. The aim was to disentangle the observed biomass decline and to understand which biological processes are actually behind it.
The data are based on two major research programs. On the one hand, the researchers used data from the Jena Experiment, which investigates grassland plots with deliberately varied levels of plant species diversity. On the other hand, data from the Biodiversity Exploratories were included, which monitor real, managed meadows and pastures with different intensities of land use.
In both programs, insects and spiders were regularly counted, identified, and weighed over many years. This made it possible to track how arthropod communities change under different ecological conditions – both under controlled experimental settings and in real agricultural landscapes.
Species loss as the central mechanism behind biomass decline
The central finding of the study is clear: More than 90% of local arthropod biomass decline is driven by the loss of species. Short-term fluctuations, smaller body sizes, or declining numbers of individuals within species do not explain the decline – the decisive factor is the disappearance of entire species.
Insect biomass declines primarily because species disappear – not simply because there are fewer individuals.
The study thus makes visible how well-known pressures such as intensive land use, pesticide application, or habitat loss act biologically: they do not merely lead to fewer animals, but to species disappearing completely from communities.
A clear temporal pattern also emerged. In the early years, it was mainly a few, but large insect species that were lost. These species were often rare, but due to their body size contributed disproportionately to total biomass. Their disappearance therefore had a particularly noticeable impact.
Over time, the picture changed. Increasingly, common species that had previously formed a stable component of insect communities also disappeared. As a result, communities lost more and more of their structural backbone.
In the end, it no longer mattered which species disappeared. Whether large or small, rare or common – each additional species loss caused biomass to decline further. Changes in individual numbers within the remaining species contributed little to the overall loss. The main driver of the decline was therefore not “fewer animals”, but the disappearance of entire species.
At first, a few rare, large species disappeared. Later, common species were also lost.
The study also showed that areas with high plant species diversity and low land-use intensity host larger and more species-rich arthropod communities. There, existing biomass is distributed across many different species. This diversity makes systems more resilient to disturbances. Where plant diversity is lacking and land is intensively used, communities shrink more quickly. Biomass becomes concentrated in only a few species, and ecosystems become ecologically less stable.
Why species loss weighs so heavily
(© Ralf Hüsges, CC BY 2.0, via Wikimedia Commons)
Insects and spiders form the backbone of food webs in meadows and pastures. They feed on plants, serve as prey for birds and other animals, and help decompose dead organic material. In this way, they ensure that food and energy circulate through ecosystems – from plants to animals and back into the soil.
When their biomass declines and becomes concentrated in fewer and fewer species, this interaction is thrown off balance. This is because the loss of species also means the loss of their specific ecological roles. Some species are particularly important for decomposing organic matter, others provide crucial food resources for birds, amphibians, or small mammals.
If only a few functionally similar species remain, food webs become simpler and more vulnerable. Such systems are far less able to cope with stresses such as heat, drought, or further human disturbance.
There is an important distinction here: declining numbers of individuals within a species could recover under favorable conditions. The complete loss of a species, by contrast, is usually permanent. With every species that disappears, ecosystems are irreversibly impoverished – even if other species temporarily become more abundant.
What can be done to counter species loss?
The study does not provide new answers to the question of why insects and other arthropods are disappearing. However, it does show where conservation measures need to focus. It is not enough to promote more individuals in the short term; above all, it is essential to maintain and strengthen species-rich communities.
Key approaches include the protection of diverse, flower-rich meadows and pastures and a less intensive use of these areas. Where plant diversity is preserved and habitats are not excessively stressed, stable insect and spider communities can develop in which biomass is distributed across many species. Such systems are more resilient to disturbances and lose their ecological functions more slowly.
Although the study’s results refer to local arthropod communities in temperate grassland ecosystems, similar relationships have been described in other regions and habitats as well.
The scale of the crisis
The Krefeld Study revealed how severe the decline in insect biomass has been over recent decades. The new analysis now shows why this decline has such far-reaching consequences. It makes clear that biomass loss is not just about falling numbers, but about the ongoing disappearance of biological diversity. Biomass losses are therefore not an isolated phenomenon, but the measurable outcome of a profound process of species extinction.
When species disappear, more than just weight is lost. Ecological functions, stability, and ultimately the foundations of resilient ecosystems are lost as well.
Sources
- Coester, C. (2025, December 2). Majority of local insect biomass decline linked to species loss. Friedrich Schiller University Jena. https://www.uni-jena.de/en/375573/majority-of-local-insect-biomass-decline-linked-to-species-loss
- Wildermuth, B., Bröcher, M., Ladouceur, E., et al. (2026). Arthropod species loss underpins biomass declines. Nature Ecology & Evolution, 10, 83–94. https://doi.org/10.1038/s41559-025-02909-y
About the author: Doreen Fräßdorf
Doreen Fräßdorf is the author and publisher of artensterben.de. She researches and writes about extinct and endangered species in the modern era, with a focus on red lists, scientific studies, historical sources, and current conservation efforts. The goal is a clear, evidence-based overview of biodiversity loss and species protection.
She is also the author of a non-fiction book about extinct modern-era mammals.
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