In short, the female hornet hoverfly will seek out a wasp or hornet nest to lay its eggs in the nest. The hoverfly larvae develop in the nest and eat the detritus (dead or dying hornets and larvae). Today we witnessed the hornet hoverfly behaviour of seeking out a hornet nest to lay its eggs first-hand on an allotment site in Reading.
On the allotment site an allotment plot holder told us about a bee nest near his allotment plot. When we had a look it turned out to be a hornet nest with hornets buzzing in and out of the entrance to the nest in an old compost heap.We watched the hornets flying in and out for a while before we discovered a female hornet hoverfly (easy to recognize as it has the eyes separated with a wide yellow band) sitting on a nettle leave near the entrance.