In the 1950s, Swiss farmers intensified and mechanized their fields; nine decades of records now reveal an unexpected divide: butterflies are still struggling, while forest beetles have fully bounced back

The insects you grew up spotting in backyards and open fields are quietly vanishing, and a sweeping new study confirms we've been watching it happen for nearly a century.

According to a study published in Nature Ecology & Evolution, researchers tracked 811 species of butterflies and deadwood beetles in Switzerland from 1930 to 2021, one of the longest insect diversity records ever compiled. Led by Agroscope scientist Felix Neff, the research combines records from citizen naturalists, long-term monitoring schemes, and formal research projects, using the national archive of info fauna, Switzerland's biodiversity data center. The results are hard to ignore. Today’s butterfly species are well below the number recorded in 1930, with an average decline of 12% across the country, rising to 29% in the Swiss Plateau and 13% in the Northern Pre-Alps, the areas of greatest intensity of agriculture and urban settlement.

The era of farm machines broke something
According to Nature Ecology & Evolution, the largest losses coincided with the period of agricultural mechanization and intensification between 1950 and 1980. Across Europe, traditional small-scale farming was replaced by synthetic fertilizers, pesticides, and large-scale machinery. Open meadows, wildflower strips, hedgerows, and diverse, wildlife-rich landscapes were flattened and homogenized to maximize crop yields. The structural variety that insects depended on disappeared.


Butterflies need sunny, plant-rich open land to survive, and their decline continued through the 1980s and has never meaningfully recovered. Nature Ecology & Evolution says specialist species, those that rely on particular plants or specific habitat conditions, were hit the hardest. The auspicious burnet moth, adapted to particular grassland conditions, saw declines of up to 41% over the 90-year study period.

Forests weren't spared either. The same push for productivity that harmed open farmland also reshaped European forests, according to Nature Ecology & Evolution. In the 19th century, forestry focused on maximizing timber yield, including the harvesting of old-growth stands and the clearing of deadwood, the very habitat on which deadwood beetles depend. The larger species, such as the hermit beetle, suffered the most, as the massive old trunks they need are rare even today.

Beetles bounced back; butterflies did not
According to Nature Ecology & Evolution, deadwood beetle species declined on average until about 1960, stabilized and have since recovered to about 1930 diversity levels, especially since the 2000s. Warmer temperatures helped thermophilic species like the European stag beetle expand their ranges northward. Two big storms, Vivian in 1990 and Lothar in 1999, also threw down large amounts of deadwood, recreating beetle habitat accidentally across the forests. Butterflies had no such stroke of luck. According to Nature Ecology & Evolution, they kept falling well into the 1980s and are still way below their historical diversity levels today.

This is not a European problem
The broader decline in insect populations is well documented outside Switzerland, too. In a PLOS ONE study, Hallmann et al. found that flying insect biomass in 63 nature reserves across Germany declined by more than 75% in just 27 years and that the decline was consistent across all habitat types, suggesting widespread agricultural and pesticide pressures rather than any local cause.

The US is not immune, either. According to a study published in Science, researchers found that the total abundance of butterflies in the contiguous United States declined by 22% between 2000 and 2020, based on more than 76,000 surveys of 554 species. In other words, for every five butterflies present in 2000, only four remain today. The same Science study found that 33% of butterfly species examined during that period saw significant declines, while only 3% saw any increase. According to the Xerces Society for Invertebrate Conservation, monarch butterfly populations have dropped by more than 80 percent since the 1990s in central Mexico and by more than 95 percent since the 1980s along the California coast.

Conservation is helping but not fast enough
According to Nature Ecology & Evolution, thanks to environmental protection measures since the 1990s, including biodiversity-friendly forest management, deadwood preservation zones and agri-environment programs, the beetle has partially recovered. But the researchers say present efforts for butterflies are not nearly enough. PNAS research on agricultural intensification and insect biodiversity shows that the last half century of farming intensification is directly linked to insect losses globally, meaning the solutions need to be at that scale: more natural vegetation, less pesticide dependency, and dramatically expanded biodiversity priority areas.

Ninety years of data are sending a clear warning. Butterflies have short life cycles and the biological ability to bounce back, if only the landscapes they require are restored. The question is whether land use and policy can catch up before the losses become permanent.