A.C.
When I was growing up, my next door neighbor was an older Mexican woman whom we called Nana (we hung out with her grandsons all the time and that's what they called her and as we got older she really was like a grandma to us so the name stuck), anyway, she would hang the ziplock bags full of water all around her unscreened porch in the summer and there were never any flies in there! I remember asking her about the bags and she told me thats what they were for. Years later, as an adult, we would go to family bbq's over there and the bags were still there and there were still no flies! I don't know why it works but it does!