Beyond declines: complex and context-dependent responses of Lepidoptera communities under climate change

Species and ecosystems are being reshaped under intensifying human pressures. While insects have often been overlooked in biodiversity assessments, recent reports of dramatic declines have drawn increasing attention from researchers and the wider society. However, systematic evaluations of change for insect taxa remain scarce due to a lack of monitoring data. Lepidoptera (butterflies and moths), a mega-diverse group sensitive to environmental change, are an exception, as they benefit from extensive long-term monitoring and trait databases, making them an ideal model for assessing insect responses to global change drivers. On the other hand and despite many studies focusing on Lepidoptera, comprehensive analyses across regions and taxa are still lacking. We compiled a global database integrating more than 100 monitoring schemes and over 12 million abundance records from thousands of species spanning several decades and including over 40 countries. We estimated temporal trends in species richness, total abundance and evenness using hierarchical Bayesian mixed models, after spatially gridding the data and applying sample-based rarefaction across years. Despite the breadth of these data, records remain heavily biased toward temperate regions in the global North, with tropical regions underrepresented. On average, Lepidoptera communities have become more diverse and more even. Yet these trends are highly context-dependent and strongly influenced by local temperature change, with stronger effects observed in areas experiencing rapid warming. Abundance dynamics were complex, differing between butterflies and moths, and driven disproportionately by common species that shaped relative abundance patterns over time. These findings highlight the multifaceted impacts of temperature across space and time, with communities restructuring along divergent pathways. They underscore the importance of evaluating multiple dimensions of biodiversity to capture the full scope of ongoing change. While results are preliminary, this global synthesis provides a foundation for understanding insect biodiversity responses and for guiding conservation strategies in a rapidly changing world.