We've just got back from a holiday in Corfu where we were plagued by wasps when we were eating. The waiters used to burn ground coffee in a receptacle because some of them believed the smoke kept the wasps away. We weren't sure but on Bank Holday Monday we had a BBQ with friends and being plagued by wasps we lit some ground coffee and the wasps disappeared!  Is it simply that the wasps don't like the smoke and burning anyhting will do (the coffee takes a long time to burn so worked really well) or is it something specific in the coffee smoke that affects the wasps?  Is there a better solution for keeping wasps away?