On occasion a homeowner may find an unusual number of large black sluggish flies in the home. At first thought, one may believe that flies are a variety of filth fly. Very likely the invaders are not filth flies at all. The unwelcome guest may be a cluster fly or attic fly. In examining the difference between filth flies and cluster flies, we find out that while filth flies are drawn to decaying matter and human foods, the cluster fly has no interest in either source for nourishment therefore not being carriers of bacteria or disease.
Let us discuss the uniqueness of cluster flies. Cluster or attic flies appear in late fall through winter. The attic fly does not develop from breeding through the development process inside the home or structures like filth flies do. The cluster or attic fly appears from hiding places or cracks, crevices, or from wall voids in the home and gather at windows giving the idea that they want out of the home instead of staying inside the home.
The development of the attic flies started with eggs being laid in cracks and crevices in the soil. When the eggs develop into larvae, the larvae attach themselves to earthworms, becoming parasitic in nature. Once adults emerge from the soil, breeding begins and the process starts all over again.
As warm fall days give way to cool nights, the adult attic or cluster fly searches out cracks and crevices around homes to tuck in to overwinter. These areas include soffits, voids around windows and doors and under or behind siding and brick.
The best strategy for treatment is as follows:
- prevention by sealing cracks and crevices before the flies find their way into the home and
- place a residual insecticide around such areas along with rooflines where shingles meet the edges of the decking.