The hoverflies are almost all gone now: I only saw one on my walk round the lakes yesterday. So here is a photo of one from back in mid-summer: an all black hoverfly, probably Cheilosia sp. (Diptera: Syrphidae). The genus Cheilosia contains a lot of all black species and it would be rash of me to try to narrow down the classification any further.
Photo taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2009-07-27.