We had a ceramic grate in the kitchen (for when there was a larder there) and found that there were a LARGE number of wasps flying in and out of there. So a quick squirt with a wasp killer spray followed by expanding foam polyfilla.
Next day, dries up and all OK.
Day after, lots of holes in polyfilla and wasps entering freely again.
So...
Wasp Nest Destroyer followed by a large hammer, followed by two bricks and mortar and they aren't eating through that to get back in :-)
Cheers,
Andy