Samenvatting
Urbanisation represents one of the most pervasive and rapidly expanding forms of land-use change globally, with
profound consequences for insect biodiversity. Butterflies (Lepidoptera: Papilionoidea) are widely used as biodiversity
indicators due to their sensitivity to habitat change, well-documented taxonomy, and appeal to citizen scientists. This
study presents a comparative analysis of butterfly taxonomic diversity across urban, semi-urban, and peri-urban habitat
gradients in three mid-sized European cities—Vienna (Austria), Bologna (Italy), and Leiden (Netherlands)—using
standardised transect walk surveys conducted across four seasons over two years (2018-2019). A total of 187 butterfly
species from 6 families were recorded across all sites. Urban core habitats supported significantly lower species richness
(mean 24.3 species per site) compared to semi-urban (mean 48.7) and peri-urban (mean 67.4) habitats. However,
functional diversity and community composition analyses revealed that urban green spaces, particularly botanical
gardens, cemeteries, and linear green corridors, support disproportionately high conservation value relative to their small
area. Generalist and migratory species dominated urban cores, while specialist species associated with calcareous
grassland, wet meadow, and woodland edge habitats were largely restricted to peri-urban zones. Urbanisation intensity,
measured as impervious surface cover, was the strongest predictor of species richness decline (R2 = 0.74). Green
infrastructure connectivity and native plant cover were identified as the most actionable variables for enhancing urban
butterfly diversity