A female picture-winged fly Urophora cardui (Diptera: Tephritidae). I first saw one of these early last summer, but at the time I had just packed my camera away and the fly got away before I could photograph it. Over the following months I would often look for it in the same place, but without success, and I eventually gave up. Then, a few days ago, I stumbled across a second one, hiding between the spines of a thistle about 20 metres from where I had see the first. The larvae of U. cardui develop within large galls in the stems of thistles, and I have seen several of these galls in the same area over the past couple of years.
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2010-06-07.