Cluster Flies

Unlike the common house flies, (Musca domestica), cluster flies (Pollenia rudis), don’t become a problem until late autumn as nighttime temperatures begin to fall.  Cluster flies, which are slightly larger than the house fly, begin to congregate on the west and south facing sides of buildings, where the long afternoon sunshine warms the surface.  Like the Asian beetles which show up slightly later, they look for cracks, crevices, holes in screens, vents and other unsealed openings around conduits and pipes extruding from the structure.  Those that have experienced this invasion are all too familiar with the large number of these somewhat innocuous pests covering the inside of your windows on warm sunny winter days.  They can leave small dark-colored spots of excrement on windows and walls, but are not known to cause any serious disease to humans.  Observables gaps and other possible entrances should be sealed, and in many cases a strategically placed application consisting of a synthetic pyrethroid and applied by licensed pest management professional may be advisable and or necessary.  Once these flies gain entrance, as with the Asian beetle, the vacuum may become your next line of defense.

Information for this content was obtained from an article authored by Steve Jacobs Sr., Penn State College of Agricultural Sciences, Department of Entomology, and through experience from the owner/applicator of Bug Control Specialists LLC.