In the archives of Swiss natural history lies an extraordinary document of ecological change: 90 years of insect records stretching from 1930 to 2021, tracking 811 species of butterflies and deadwood beetles through the most turbulent century in European land use. The story that emerges is one of dramatic collapse, surprising recovery, and a widening chasm between winners and losers in the natural world.
When midcentury mechanization swept across Switzerland's countryside, the impact on its insects was swift and severe. Butterflies began their long decline in the 1930s, plummeting especially sharply during the 1950s and 1980s as farmers intensified agriculture, drenched fields with pesticides, and smoothed the landscape into productive monotony. Deadwood beetles followed a similar arc, crashing as foresters harvested old-growth stands and cleared fallen timber to maximize timber yields. Yet here is where the trajectories diverge: deadwood beetles have rebounded to 1930 levels since the 2000s, while butterflies remain stuck, on average 12 percent below where they started—a gap that widens to 29 percent in the Swiss Plateau, the nation's most heavily farmed and built-up region.
The research, published in Nature Ecology & Evolution by teams at Agroscope and the Swiss Federal Institute for Forest, Snow and Landscape Research, relies on an unusual and precious resource: historical records from enthusiast naturalists combined with modern observation data. "People have always been fascinated by large insects such as butterflies and beetles. Consequently, there are numerous historical specimens, as well as reports in modern observation apps," says Felix Neff of Agroscope, the study's first author. This citizen-science archive became a window into the past.
The recovery of deadwood beetles owes much to changing forest management. Since the 1990s, Swiss foresters have increasingly adopted biodiversity-friendly practices, leaving old-growth patches and deadwood standing rather than clearing them entirely. Climate change, paradoxically, has also helped heat-loving beetle species expand northward and flourish. Violent storms—Vivian in 1990, Lothar in 1999—scattered massive quantities of deadwood across forests, creating unexpected habitat bonanzas for species like the European stag beetle and the Aromia moschata, which became rare mid-century but has since recovered.
Butterflies tell a different story. Most species depend on sunny, open meadows rich in wildflowers, habitats that continue to shrink under agricultural and residential pressure. Specialist species like the auspicious burnet moth, tied to specific plants and microclimates, have suffered catastrophically—some experiencing declines of up to 41 percent. While some agri-environmental programs have been established, they remain insufficient to reverse butterfly losses.
The study reveals an uncomfortable truth: recovery is possible, but it requires sustained effort and comes unevenly. Kurt Bollmann of WSL notes that "conservation measures are having an effect, particularly in forests," but emphasizes that "more intensive efforts are still needed for numerous specialized species, like many butterflies." The ninety-year record is both encouraging and cautionary—proof that human action can bend ecological trajectories, and proof that without it, species disappear.