Get an IR camera. You should be able to find cracks/leaks/whatever real easy. Unfortunately IR cameras aren't cheap, so perhaps you can call a HERS guy to come over with one and pay him $100 for his trouble.

If that fails, I suppose you could fill your house up with a smoke machine and attach a blower door (you'd need the help of a HERS guy again)... or just use a smoke pencil.

A $3 can of wasp spray will do the trick. Hit them at dusk, soak down the nest. The nest will be empty come morning. Some sprays say on the label that they will repel wasps for a couple of months. I always carry several cans of spray in my truck as I run into them constantly when working on houses. Go get um !!!!