The hoverfly season is now in full swing with new species appearing almost daily. This is a female Xanthogramma pedissequum (Diptera: Syrphidae). I did glimpse one of these on each of my two previous walks around the lakes, but this was the first I managed to photograph this year.
However, I did photograph a male of this species last September; see here.
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2010-05-31.