|Common Name||Scientific Name|
|Cluster Fly||Pollenia rudis (Fabricius)|
|Face Fly||Musca autumnalis (DeGeer)|
Cluster and face flies are found in homes, churches, hospitals, apartment complexes, commercial and public buildings and other structures. These large, sluggish flies, sometimes called "attic flies," appear on warm, sunny days during late autumn, winter and early spring. They occur in large numbers, especially at windows and in rooms not frequently used. They make irritating, buzzing noises, spin around and move sluggishly. When crushed, they leave a greasy spot on upholstery, carpets and wood surfaces. Cluster flies in hospitals may carry infectious bacteria on their bodies. They do not bite humans nor feed on structures or furnishings. Buildings or houses located on an exposed hill top are attractive sites.
Adult cluster flies resemble house flies, but are slightly larger, about 5/16 inch long, narrower and nonmetallic gray. When at rest, they overlap their wings at the tips, whereas the house fly does not. Also, the thorax is without distinct stripes, contains many short, yellow-golden hairs, and the dark gray abdomen is hairy with light and dark patches of color. When crushed, the cluster fly has an odor resembling "buckwheat honey."
Adult face flies are similar in appearance to house flies except for being larger and darker. Male face flies have large, compound eyes that nearly touch on top of the head, whereas house flies do not. Female face flies have a silvery stripe around the eyes in contrast to the golden-like stripe of the house fly. The face fly has a slate-gray thorax.
Female cluster flies lay eggs singly in soil cracks and crevices in the vicinity of the earthworm, Allolobophthora spp. Eggs hatch in three days and the larvae (parasitic stage) penetrate and develop in the bodies of earthworms. This larval stage lasts 13 to 22 days, and the pupal stage, 11 to 14. The life cycle is completed in 27 to 39 days. There are about four generations during the summer. Populations vary from year to year, sometimes worse after wet summers.
Adult cluster flies move to protected places to hibernate (overwinter) when the days shorten in mid-August. Flies cluster on the warm sides of buildings in late summer during the day. As the sun goes down and temperatures cool, flies crawl into the building through cracks, especially under eaves, gaps in siding, etc. Large numbers may group together (cluster) in attics, unused rooms, wall voids, basements, tree holes and other darkened sites. They are attracted to light, light-colored siding and structures on lawns and pastures inhabited by earthworms. They enter rooms through sash-cord openings, cracks in windowsills or baseboards, loose-fitting vinyl or aluminum siding, and other small openings. They become active whenever temperatures rise above 54 degrees F indoors from early autumn to mid-spring, especially around windows with sunlight.
Cluster flies do not breed in buildings but leave hibernation sites in the spring (they often swarm onto windows on warm sunny days) to return outdoors for reproduction activity. Just as they become a nuisance in the fall while seeking hibernating quarters, they are also bothersome in the spring, trying to escape.
Face flies are serious pests of cattle and horses. They often overwinter in homes and other structures near pastures where these animals are kept. Eggs and larvae develop in fresh cattle dung (not when it is crushed over). During the summer, adults annoy the faces of cattle and horses, where they lap exudation from the eyes, nostrils and mouth. The larval stage lasts three to ten days, while the entire life cycle requires 14 to 18 days.
Initiate control tactics before flies enter buildings in large numbers. (Work should be done in midsummer.) Control cannot be permanent until the openings through which these flies enter the home are closed. Both cluster and face flies, which normally live outdoors, are difficult to control after they have gained entrance into homes and other structures. They often hibernate in wall voids and other inaccessible places. It is important to prevent fly entry by using caulking compound or other suitable material to fill all cracks and openings near windows, doors, electrical outlets, switchboxes, vents, etc., especially on the south side of the buildings, where these flies most commonly enter. Seal holes, cracks and splits in siding, especially up under eave troughs and along the roof. Maintain the house in good physical condition with adequate screening and use of yellow, non-attractive insect lights. Use screen ventilators, louvers, air-conditioners, etc., with copper, bronze or aluminum screens rather than wire screens to prevent rust. For temporary indoor relief, dead, dying or sluggish flies can be picked up with a strong suction vacuum cleaner, shop-vac or broom and dustpan and discarded. A few flies can be dispatched with a fly swatter or folded newspaper.
Tests on spraying the outside of the house or structure with synthetic pyrethroids look promising. Usually only the south side of the structure is treated in mid to late August, using a fogging apparatus held within three feet of the dry surface, carefully treating areas beneath eaves and around windows, doors, attics and unoccupied lofts.
Only the licensed pest control operator or applicator can use cyfluthrin (Optem, Tempo), cypermethrin (Cynoff, Cyper-Active, Demon, Vikor), deltamethrin (Suspend), lambdacyhalothrin (Commodore) and tralomethrin (Saga). Other pesticides labelled include amorphous silica gel (Tri-Die), boric acid (Perma-Dust), chlorpyrifos (Duration, Dursban, Empire, Engage), permethrin (Astro, Dragnet, Ectiban, Flee, Prelude, Torpedo), propoxur (Baygon), pyrethrins (Exciter, Microcare, Pyrethrum, Uld, X-Clude) and resmethrin (Vectrin).
Usually the licensed pest control operator or applicator does the control job best due to availability of restricted pesticides and special equipment. Before using any insecticide, always read the label and follow directions and safety precautions.
Since cluster flies outdoors reproduce in earthworms and face flies in fresh cattle dung, there is no practical, economical control method against their breeding places. Both cluster and face flies usually hibernate in the wall voids of homes where they periodically emerge on warm winter days and early spring. Killing visible flies with space sprays and fogs does not give satisfactory control as additional flies are usually under insulation or deep in cracks and crevices. Also, flies will often continuously emerge from openings around window pulleys, window and door casings, under baseboards, tops of wall studs, etc.
When infestations are light and openings are easy for application, household aerosol space sprays, with tube injectors into the wall, can give good kill. Aerosol sprays of pyrethrins, resmethrin, chlorpyrifos (Dursban) or propoxur (Baygon) can be effective. Best control is achieved with dust formulations which not only kill the flies moving within the wall voids, but will leave a long-lasting residual which will kill additional flies becoming active later. Fly paper, sticky strips and bug zappers are of little if any value since flies do not fly around much in space. Sometimes, a professional fly control electrocuter, placed within suspended ceilings of commercial buildings by pest control operators, are helpful.
Piles of dead flies left in the walls can sometimes lead to secondary infestations of carpet or larder beetles and rodents. Crack and crevice treatments, before installing storm windows and doors in early autumn, can be helpful.
This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868