Environmental drivers of the diversity and distribution of black flies ( <scp>D</scp> iptera: <scp>S</scp> imuliidae) in the <scp>B</scp> alkan Peninsula

Abstract Black flies (simuliids) are an ecologically and medically important group of cosmopolitan insects whose distribution is influenced by climate and landscape changes. This study aimed to analyse diversity, distribution and frequency of simuliid species in the Balkan Peninsula, investigating how their ecological patterns relate to both regional geographic factors and local habitat characteristics. Total of n = 40,733 larvae and pupae (45 taxa) were collected from 256 sites from 2010 to 2021. Localities were categorised by catchment basin, hydro‐ecoregion and predefined watercourse types. Distribution, land use and diversity measures were analysed. Altitude and 19 bioclimatic variables were included as continuous environmental predictors. Simulium ornatum, S. reptans, S. variegatum and S. balcanicum were the most frequent. Overall species richness ranged from 1 to 8 taxa, influenced by bioclimatic factors and land use, with peak richness observed under moderate anthropogenic disturbance. Species replacement was a significant component of beta diversity. Altitude significantly influenced assemblage composition. The key bioclimatic drivers included precipitation during driest/warmest periods and mean temperature of the wettest quarter. Hierarchical clustering identified nine distinct simuliid assemblage groups, confirming altitudinal niche differentiation consistent with Rapoport's elevational rule. Higher altitudes are dominated by the S. variegatum group and the genus Prosimulium , while subg. Wilhelmia was characteristic of lowland sites. Diversity distances between simuliid assemblages were also correlated with geographic distances between sampling sites. This study provides a valuable baseline for understanding the complex spatial and environmental drivers of simuliid diversity in the Balkans, crucial for future ecological and conservation research.