Abstract <p>Understanding long-term biodiversity dynamics is essential for effective conservation planning, yet historical baselines remain underexploited in insect studies. Here, we assess changes in butterfly (Lepidoptera: Rhopalocera) communities over nearly a century in a municipality in western France, using two complementary datasets: a historical collection sampled by a single naturalist between 1927 and 1933, and a modern dataset compiled between 2000 and 2025 from validated citizen science records and standardized surveys. A total of 59 species presence data were combined with a comprehensive life-history trait database to explore patterns of probable local extinction, persistence, and colonization. We document a moderate turnover around 27% in species composition over the century, with a decline in species richness and the disappearance of several habitat specialists. Moreover, the comparison of land use between ancient and contemporary period using aerial photographs enabled to highlight the damages effecting bocage landscape and riparian forests. Trait-based analyses reveal that species apparent persistence is associated with a shared set of ecological characteristics, including variability in forewing length, broader habitat tolerance, and generalist host plant use. In contrast, species presumed losses are more functionally diverse, suggesting multiple, trait-specific extinction pathways. Colonizing species exhibit trait profiles distinct from both persisting and disappearing taxa. Our findings highlight a trend toward functional homogenization of butterfly communities, driven by environmental filtering. Occupancy in recent period was correlated with persistence of species at the global level as well as at the functional groups.</p> Implications for insect conservation <p>This study underscores the value of historical data for detecting long-term ecological changes and for informing conservation strategies that prioritize functional diversity and resilience at the local scale.</p>