Fill a plastic, see-thru, bag half full with water. Hang it shoulder high next to the door. It works for me! The water in the bag somehow screws up the fly's sense of sight and they avoid the area of the water bag. I had houseflies and horseflies galore until I tried this. Now I have two or three at a time and that's it. We could count as many as 25 flies on the kitchen windows at any time until we put up the water bag. Good luck. Make sure it's hung right next to the door that you're using all the time.