Hoverflies, without stings, are well known for mimicking the colours and patterns of stinging wasps so the standard issue markings for most hoverflies are some variation on the theme of black and yellow stripes. This species, Leucozonia glaucia, is the exception to the rule and is turned out in this attractive black and denim blue colour scheme ...... which begs the question as to whether it's mimicking something or is simply a genetic variant with no particular natural selective benefit or disadvantage.
According to British Hoverflies by Alan Stubbs and Steven Falk the markings on this species are normally yellow but this blue variant occurs frequently. I haven't encountered it often and this one is part of a population that lives along a woodland ride in Hamsterley Forest, Co. Durham and is often quite abundant when hogweed and angelica are in flower. This individual is a female, identifiable by the widely spaced eyes.
It seems to have been quite a good summer for some hoverflies in my part of Co. Durham. I had a quite a few of this one, which I think is a particularly attractive variant of Helophilus pendulus, in my garden where it seemed to be partial to meadow crane'sbill flowers.
I'm not completely sure what this large hoverfly species is but I think it may well be Sericomyia silentis..... a convincing wasp mimic. It's been quite common in Teesdale throughout August and early September and I've seem several on devil's bit scabious, which is supposed to be particular attractive to this species.