I have a fly problem, can't figure out why

[Steve Balinski]

Anyone ever deal with a fly problem?
I have a duplex, about 2+ weeks ago both of our units started getting flies. My unit has about 10-15 a day, the other unit has about 30+
I had Orkin come over, they didnt see anything specific that indicated where the problem was coming from. Both attics are pretty "clean", except there is evidence of a squirrel (crap) in my tenants attic, BUT no smell of anything dead, AND no swarms of flies in the attics. At this point I dont know what to do. I've been told they run their course, but going on 3 weeks seems kind of long. I'm not sure what else to do at this point.  My tenant has them all over the house, mine seems to be localized to the basement.  I put a stick trap on top of the floor drain, 0 flies on it in 3 days now, they're just all on the windows.

[Karl B.]

Hire a priest. Just kidding. 

I would have the tenant close all interior doors to try and get an idea as to where they're coming in from (the room with the most flies is likely the fly entrance). On your side if they're coming in from your basement then look to seal everything from the inside and outside. 

Since they're coming into both your unit and the tenants' unit I believe the flies could be originating from somewhere else. Are your other neighbors having the same issue?

My parents live near a horse barn (probably 300 yards away) and the barn manager doesn't keep the place very clean. The place is teeming with thousands of flies (they cover the floor - it's insane - I feel bad for the barn cats) and they make their way up to the house and get in. I bought a bunch of fly tape and gave it to the barn manager so she'd get the hint. 

You can also buy a bug zapper and put it outside. And when using a fly swatter gets boring use a shop vac - it's fun to catch them that way. :-)