In 8 years here have never had a fly problem like this. We had a pet sitter here for a week (week before last), and noticed some flys in the house after assuming she left the door open, but not this bad. We can't find any trash or source, but wife has killed 24 house flys in the house today. I killed 2 (she's just more dedicated than me). The flys are in the windows mostly, but no open windows, doors are closed mostly. They aren't that bad in the yard. . .Any suggestions?