Last year over summer we has what it seemed like, and probably was a million and one flies come into the house. We had only been living here for about four months and it was driving us crazy as the nice breeze came through the back door, but so were the flies. Out by the beach where we use to live never had this problem.
So over the winter months hubby organised this door to go up and this year hardly any flies at all. We can have every other door and window open some with screens and others not and still hardly no flies. They just loved coming through this door only and if anyone does leave it open ..... fly explosion.
I think it is one of the best things that has been done in the past year to this house, along with insulation we got, but that is another whole story and I will just say, if you haven't get your house insulated you don't know what you are missing.