I received a bee house for Christmas and it remained unoccupied all spring and summer, and today I noticed that some of the holes are finally plugged up! This afternoon when I was observing the house, I noticed smooth yellow and black wasp-like creatures going in and out of the holes, not fuzzy mason bees. I also noticed tiny "bees" investigating the mud plugs. What kind of critters are these? Are these good insects?

FYI- The house was homemade by my sister-in-law out of a piece of old barn wood in which she drilled holes of various sizes, following a plan she downloaded from the internet. There are no straws in the holes. I live in suburban Ft. Worth, Texas btw.