The distribution map of the hoverfly Eristalis pertinax may be telling a story about failed clean water regulations:
“Eristalis pertinax is a European hoverfly. Like Eristalis tenax, the larva of E. pertinax is a rat-tailed maggot and lives in drainage ditches, pools around manure piles, sewage, and similar places containing water badly polluted with organic matter.” https://www.inaturalist.org/taxa/52490?locale=en-GB
Caveats: sampling bias, and unknown distribution prior to modern waterways pollution.
