Latitude and evolutionary history shape the global distribution of migratory butterflies

Haiyu Li , Shawan Chowdhury , Qiushuang Liang, Wei-Ping Chan, Zunyi Xie, Rohan Clarke

Hundreds of butterfly species migrate globally. Seasonal migration allows butterflies track suitable environments across large distances, yet global distribution patterns and the processes that shape them remain poorly understood. Here, using season-specific habitat suitability maps for 426 migratory butterfly species, we assess how morphological traits, environmental conditions and evolutionary history shape their distributions. Our analyses reveal that migratory butterfly richness peaks at ~12° N, and the Nearctic and Palaearctic realms together contain 64% of the global area of high-richness assemblages. Species concentrated in tropical regions occupied smaller geographic ranges, whereas range size increased with wingspan. The average wingspan declined with increasing latitude, but this association was not significant after accounting for phylogeny. Bayesian phylogenetic models revealed significant phylogenetic structure in geographic range size, suggesting that evolutionary history contributes to contemporary range constraints. We show that while migratory butterflies can track seasonal environments, environmental variation, morphology, and evolutionary history largely determine their distributions. Our findings highlight tropical and subtropical regions as monitoring priorities and the need to maintain seasonally suitable habitats across migratory ranges.