Brimstone butterfly on a thistle head

I caught this on a walk around Oversley Wood near Alcester. I had been told there were Purple Emperors to be seen but I was disappointed; however there were many numbers and varieties of butterfly most of which I failed to photograph as they were very skittish, so an early morning might prove more fruitful. Anyhow, I managed to get close enough to this fellah to avoid cropping the image afterwards.