Hey everyone,
I’ve been noticing small black flies gathering around the inside of my windows lately — mostly in the kitchen and the upstairs hallway. I’m trying to figure out whether this is a drain issue, something decomposing in the walls, or just random outdoor flies getting in.
I had a similar issue last summer and it turned out to be moisture building up under the window trim. Once I dried everything out, the flies stopped showing up within a week.
Could be drain-related, but if they’re staying near windows, I’d lean more toward them coming in from outside. Are you near any trees or standing water?
From my experience, when flies cluster at windows, they’re usually trying to escape from inside, not enter. Might be worth checking any sink traps nearby just in case.
I second what @BugScout91 said, if they’re bouncing off the glass, they probably originated indoors. Maybe run some really hot water down the kitchen drain and see if it makes any difference.
I had window flies once because something died in the attic vent. The smell was faint but the flies were a big clue. Not saying that’s your case, but if you’ve got an attic above that hallway window, maybe peek inside.
They could just be fungus gnats if you’ve got houseplants near the windows. The humidity from the soil attracts them like crazy.
If you think it might be plumbing, check any nearby bathrooms. I had black drain flies appear in only one corner of the house, and it ended up being a slow-leaking pipe behind the wall.
Hey @NorthsideDad, did the flies disappear immediately after fixing the leak? Curious because I’m dealing with something similar.
Tape a clear plastic bag over the window frame for a day. If the flies show up inside the bag, they’re coming from cracks or gaps in the frame.
Sometimes it’s just seasonal. We get small black flies every June whenever the weather suddenly warms up. They hang around the windows for a week and then vanish. Hopefully yours is just a short phase too.