I have flies in all the front windows of the house. I can't identify where they are coming from. I have sprayed bug spray, which kills them but when I go back to check a little bit later I have more flies. My house is very clean. I have checked the trash. I don't know where they are coming from. I have my central air on so no windows have been open for some time. Please help. I have been racking my brains trying to figure out where they are coming from and how to get rid of them. I live in Philadelphia. I had this same problem 2 years ago in the beginning of May. It lasted for a few days and they dissappeared.