This damselfly is eating another bug, some kind of little fly. I watched it chewing for a long time. All the others in the vicinity got spooked when I got too close, but this one was very intent on its meal and didn't move away. What I couldn't see until I zoomed in on the image was what a messy eater he is--there are scraps and chaff all over his head and on the brick wall, and you can see the wing sticking out of his mouth.
Absolutely enlarge this image.