I'm no entomologist, but we have also had a lot of flies in the house lately...(late September). I discovered mine all like to sit between the window and the miniblinds in an east window in the morning when the sun comes in. Could it be the warmth? After all, the days have been chillier, probably our house is too....maybe your electrical stuff is warm. Anyway, I was glad to find their hiding place, it means I can swat a bunch all at once!