Large gray flies collecting around Michigan windows can look strangely out of place, especially when they appear in noticeable numbers near the end of summer or during the first cool weeks of fall. They may sit quietly on the glass, crawl across the window frame, or cover a sunny section of the exterior wall without showing much interest in anything inside the house.
These are often cluster flies, a group of flies with a seasonal habit that is very different from the common house flies found around food and garbage. Their gatherings around Michigan homes are usually connected to changing temperatures, sunlight, and the search for protected places where they can spend the winter.
Michigan’s transition from warm summer weather to cold autumn conditions makes this behavior particularly noticeable. A few warm afternoons can bring the flies back to sunny walls, while increasingly cold nights encourage them to investigate cracks, rooflines, attics, and other sheltered parts of a home.
Those Large Gray Flies Are Often Cluster Flies
Cluster flies are noticeably larger than the ordinary house flies most homeowners are accustomed to seeing. Adults generally have a grayish body with darker markings and fine golden-colored hairs on the thorax that can be easier to see when the insect is viewed closely…