Recording of an exceptional aggregation of Milesia crabroniformis in a forest of Northern Italy

Milesia crabroniformis (F.) is a large hornet-mimic hoverfly considered relatively rare in Italy. During visual samplings along a transect carried out in Castiglione dei Pepoli (Bologna, Italy), with the aim of monitoring changes in hoverfly communities over sixty years, the authors observed and counted at least one hundred specimens of this hornet-mimic hoverfly while forage on Sam-bucus ebulus L. This note aims to document this very infrequent behaviour of M. crabroniformis to contribute to the understanding of this phenomenon.