A friend directed me to your site. I have, what of course I think, are some interesting photos of a hornet’s nest being built over a birdhouse. Apparently, cold Minnesota winters warrant building nests with extra insulation! I am attaching one, but if you are interested in more, let me know. In this view you can see the hornet’s have are working on the nest and have built not only on the outside, but the inside as well. Enjoy.
Your photo is pretty great. The builders are Yellow Jackets. Mom in Ohio frequently gets paper wasp nests in her birdhouses. We have also gotten images of Red-Tailed Bumblebees building in birdhouses. Perhaps someone should market the wasp and bee house.