Yes. Cluster flies can shelter inside upper parts of buildings and then emerge into upstairs rooms when temperatures warm their hiding places.
There are different species of flies and they behave differently. Some breed indoors, but there are others that tend to enter properties before winter and to get away from the cold. It helps to know which one you are dealing with.
Cluster flies typically enter structures before winter. Attics, wall voids, siding gaps, and other protected areas provide places to remain during cold weather. Because many of these spaces are high in the building, activity can be worse upstairs.
Sunlight is another big factor. Like other overwintering insects, cluster flies tend to go for exterior walls and roof areas that catch a lot of sunlight. On sunny or warm days, flies can be compelled to wake up and start moving again when they would otherwise be dormant. This is why you can have that obnoxious experience of noticing several slow-moving flies around glass upstairs even though there is no obvious food or breeding source nearby.
If flies are repeatedly associated with garbage, drains, or decaying material, you’re probably dealing with a different type of fly. Your best bet then will be to clean the garbage or drains.
For cluster flies, prevention largely means exclusion before fall entry. Inspect upper windows, screens, soffits, vents, siding transitions, and roofline gaps. Properly seal any that you find. This will also have the added benefit of making it harder for stink bugs and boxelder bugs to get into your home as well.
If flies are becoming a problem around your Southwest and South Central Michigan property, Mosquito Squad of Southwest and South Central Michigan can help with pest control around the property. Call (269) 340-3580 or request a free quote online.
