Small, hovering sluggishly, then settling on vegetation … and quite unlike any fly I’d seen before! It turns out that the adults are not common, and their biology fascinating. The larvae live inside ant colonies, feeding on ant larva and pupae … protected by a shell! In the past they’ve even been mistaken for molluscs! Little, tank-like armoured hunters.
Archimicrodon

This is the archetypal, ubiquitous hover fly. So very unlike its cousin the ant fly. Syrphine larvae are predators of aphids and other plant-sucking bugs. The adults are commonly seen at flowers, although at this time of year they are probably relying on honeydew.
Simosyrphus grandicornis