They can. Some overwintering flies shelter in upper parts of buildings and later move toward sunny windows when they become active.
There are a lot of species of flies that don’t want to be out in the cold. So they overwinter inside warm shelter when they can find it. Oftentimes, homes are the best available structure nearby.
This overwintering behavior explains why certain flies slip into your home during the fall to hide inside the walls. As long as temperatures remain low there, they can be dormant for a while. But it's once direct sunlight warms up the exterior siding that the trapped insects are tricked into thinking spring has arrived. So from there, they'll do what instinct tells them to do and start moving toward indoor light.
Homeowners around the lakeshore will sometimes return after a long absence and find a bunch of flies in their house around windowsills even if flies weren’t a problem before they left. This does not necessarily imply the insects were breeding indoors. This matters because a lot of fly activity is associated with drains, garbage, and decaying organic matter, but again, that depends on the species.
What you see and when you see it can tell you what you’re dealing with. If you find flies mostly on sunny winter or early spring days near upper windows, then you're probably dealing with overwintering flies and not the kind that breed inside.
Prevention starts before they get inside. Inspect screens, window frames, soffits, attic vents, roofline transitions, siding gaps, and utility penetrations. Repair damaged screening and seal unnecessary openings without blocking required ventilation.
If flies are becoming a problem around your West Michigan Lakeshore property, Mosquito Squad of West Michigan Lakeshore can help with pest control around the property. Call (616) 426-6776 or request a free quote online.
