Blue Chalcid Wasp

A small chalcid wasp, probably not an Ormyrus sp. like the blue wasps I saw on oak leaves last year: the above wasp was on a thistle head (Cirsium sp), not oak, its abdomen was relatively smooth, not embossed, and its legs were mostly yellow, not black, so I feel fairly confident that this must be a different species.

Photo taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2010-06-29.