Tens of thousands of migrating hoverflies found dead on a strandline in the South of France

Abstract

Abstract Knowledge on insect migration is scattered, and we are only starting to grasp the extent and ecological impacts of their massive seasonal bioflows. Hoverflies (Diptera: Syrphidae) are one group of insects which partake in these long‐distance journeys, which are thought to have important ecological consequences including pollination, biocontrol and nutrient transfer. Yet, few sightings of mass spring migration have been documented so far. Here, we report observations of tens of thousands of dead insects on a strandline in the South of France in mid‐May 2022. Hoverflies represented 77% of all dead flying insects found on the strandline and most individuals belonged to the species Episyrphus balteatus and Eupeodes corollae, which are species known to exhibit migratory behaviour. We assume that strong winds or a localised storm were the cause behind their stranding. Putative flight origins for these insects are north‐eastern Catalonia or the Balearic Islands. This rarely documented observation enabled us to highlight the scope of hoverfly migration in spring and to discuss some of the challenges they face along their migratory route.