Besides blueberries, they seem to favour Epimediums and species roses. They are solitary bees, so without a community to spread the word about other good sources of material, they keep returning to the same source once they've found it. I don't begrudge them their harvest because they are good pollinators in the garden and the plants don't appear to suffer, except perhaps a little in appearance.
While I was there, the bee kept returning for another piece of leaf. I ran for my camera and had a stab at recording it at work. My video is a bit blurry, thanks to my lack of skill, but I'm posting it anyway, at least until I can get a better clip.Watch the top lefthand corner for the bee's appearance. (Note: I'm hearing that, if you get my blog via the RSS feed, the video doesn't load -advice on how to fix this gratefully accepted. However, it loads successfully straight from the site.)