When I do removal I always tell the users to fill the void with fiberglass insulation. On the outside to either stucco or concrete the outside and to never use the cans of Great Stuff. Now Great Stuff has it's place but when it comes to bees. The bees will win. Because it will dry and they will simply chew through it.
Now in some of the modern homes have been using the commercial version of the expanding foam as insulation in walls and ceilings. Trucks with big tanks come in and spray it. You end up with a nice insulation that isn't itch or a bunch of blown fibers that turn to mush when wet. The problem is that any small void that leads outside is a good stater point for bees.
So now I have this nice house two years old. The attic has the roof trusses sprayed with the foam. It is a decorative roof that makes for easy voids. Well the bees moved in. And I found them because you could follow the sound of them chewing the foam.
In the pictures you will see a pile of the dust created by them chewing it. http://www.brendhanhorne.com/coppermine_dir/thumbnails.php?album=166
Tomorrow I go crawl in an attic and remove these guys. It may qualify as the most difficult cut out I have had to do because I have to crawl to a very awkward corner and I cannot get to the sophet they are in.