I have a problem with flies suddenly. I have been living in my house for almost 20 years and never had a problem with flies. How can I find out where they are coming from and eliminate the source?
They are almost all on the first floor, so that would seem to rule out a source in the basement or upper floors. For example, I have a cat litter box on the second floor, but there are no flies there, so I know the flies are not coming from anywhere near there.
That would seem to leave two possibilities:
(1) They are breeding outside the house and somehow finding a way in, or
(2) There is some hidden source on the first floor
I have carefully tried to seal off any crack or opening to get into the house, yet the flies are just as numerous as ever. I do see flies outside on the windows, but in small numbers, so they could either be coming from outside, or just be escapees coming from inside the house.
I have searched the grounds very carefully for animal bodies or other organic matter and found nothing.
How can I locate the source of the flies?