Several years ago when we first moved into this house, I found a small hole in the rim joist on the back of the house and one day while working outside near that I noticed one fly in and out of that hole. Shortly after that I was stung. I went to the basement and after pulling down some of the insulation in the floor, found a basketball sized nest attached to the bottom of the subfloor
After hurrying out to the store for several cans of spray and soaking the nest and shopvacing it up, I had the nest gone and the hole sealed up. There were literally thousands of larvae in that nest ready to hatch inside my house!