Citizen science reveals a rapid range expansion of a Mediterranean hoverfly under climate warming (Diptera: Syrphidae)

Abstract

The big‑headed lagoon fly, Eristalinus megacephalus (Rossi, 1794), is a Mediterranean hoverfly historically restricted in Italy to a handful of coastal regions. Recently, numerous observations uploaded to the iNaturalist citizen‑science platform show a rapid northward and inland expansion, with new regional records from Piemonte, Lombardia, Veneto, Friuli-Venezia Giulia, Marche, Umbria, Puglia and Calabria. Here we compile Italian literature records and recent citizen‑science observations and map the current occurrence of the species in the country. The density of recent records in the Po Valley and in other inland areas suggests that E. megacephalus is no longer limited to coastal Mediterranean climates. We discuss the value of citizen‑science data for fast‑moving biogeographic updates. Targeted surveys are now needed to test whether newly observed clusters represent transient dispersers or established populations.