About two years ago I had a hornets nest inside one of the walls of my house. It's an old house, built in 1916, and it's been added onto and patched here and there, so needless to say, it's not the most critter-proof in the world. I was able to get 'em with a can of wasp and hornet spray, right to the opening. I don't know how big the nest was, but I'd say ultimately counted about 30 of their curled up, dead little bodies on the roof outside the opening and in the gutter.
I never did tear the wall apart to find out how big the nest was, and somehow I have a feeling that's going to come back to haunt me one day. That winter though, I got some of that expanding foam stuff and sprayed it in the opening. Nothing ever tore it away, so I guess I'm good there.
Those hornets were pretty creepy, because unlike mere mortal bees, they were night scavengers. On cool nights I liked to leave the windows open, with just the screen in place. They'd occasionally smack themselves against the kitchen window, hard enough to sometimes give you a startle and heart palpitation! There were always a few hanging around the outside light, too. And every once in awhile, one would find its way into the house.
They actually weren't aggressive, and I felt kinda bad killing them. But I also didn't like the idea of sharing a house with them! One night I was away, and my roommate called me, telling me that there was about 50 of the suckers crawling on the outside screen to the kitchen window. They're attracted to light, especially fluorescent light, so it's just that that draws them in, not any innate desire to attack whomever happens to be in the kitchen. Still kinda creepy though. And to be honest, I think my roommate was exaggerating on the number. I'd never seen them do that, and I think he probably embellished it to scare me into doing something about getting rid of the nest. I have to admit I was procrastinating on that little project.