Hi all, in the past few weeks we've been getting dozens of these flies in our house a day. We're baffled as to how they're getting in or where they're coming from. Here are the facts:
We get anywhere from 10-40 of these flies inside a day, with the exception of yesterday, we got zero ! We speculate it's because it was cloudy and slightly cooler, so perhaps they were not trying to escape the heat and get inside?
Today, we had 10 so far by mid-afternoon.
Our house is fairly modern (built 2015). Chicagoland area. They tend to show up between 11-5pm. They stick to the glass on the doors and windows, usually the bottom floor of the house. House is an open layout, and with the one door we have closed to the laundry room that leads out to the garage, we still get a few in the window there.
Things I've tried and looked at:
We run the A/C and keep doors and windows shut as much as possible. Removing all houseplants, including cut flowers. Taking out trash every night to a garbage can in our alley. Keeping our A/C fan on (I had a theory that they started showing up when the fan would turn off and they were coming in via the vents, but we've never seen one exit a vent, and removing the vent covers shows no obvious sign of them.). We vacuum them up with a hand-vac whenever we see them. We keep things cleaned and sprayed down. No visible holes in window screens. Inspected cabinets, pantry, etc. thoroughly for any rotten food, found none. 0 flies in the basement, and no visible entry points there either. No dead animal smells. No points outside where flies are gathering during the times they show up inside or otherwise. There's no crawl space as we have a basement, but there's an attic I haven't been able to check out as I have to buy a ladder – but even so, how would they be getting downstairs? We don't see any visible coming out of the attic entrance. We have the occasional fly or two in the garage, but no swarms, and keep the garage door closed.
Here's a close up of a dead one:
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