When full grown, the parasitic maggot leaves the body of the host and enters the soil. There are about four generations a year. Cluster flies are parasitic on certain earthworms. Complete control of cluster flies is almost impossible since the overwintering adults are concealed in walls, attics, etc. When possible, cover the louver to the attic with screen, and use a caulking compound to seal openings to the outside.
Adults are sluggish enough in the winter to be picked up with a vacuum cleaner.
Earthworms are important to soil, and cluster flies would simply come from surrounding areas. Chemical control should be concentrated in the home where the adults hibernate. Adults that buzz about the house can be killed with an aerosol spray Prevention of cluster fly infestations is very difficult, but certainly warrants a try. Timing is the most important factor. Applying a synthetic pyrethroid to the outside of the structure with an electric fogging machine will help treat all entry sites.