Pest Brief: Cluster Flies and Face Flies 101
By: Robert (Bob) Batman

NATURAL ENTOMOLOGICAL CLASSIFICATION

Phylum Arthropoda
Class Hexapoda or Insecta
Order Diptera
Family Calliphoridae (cluster fly); Muscidae (face fly)
Genus/Species: Pollenia rudis [Fabricuis] (cluster fly); Musca autumnalis [DeGeer] (face fly)

Morphosis: Complete (egg, larva, pupa, adult)

Most people can't tell a house fly, from a cluster fly, from a face fly. That's OK so long as you remember the following: 1) house flies only live about 1 and1/2 months, 2) face and cluster flies overwinter in structures! and, 3) calling a professional is probably going to be cheaper than doing it your self.

Both cluster and face flies are addressed in this Brief for the following reasons. Most residential and office cluster and face fly infestations result for the same reasons and in some cases, cluster flies and face flies, both, are overwintering in the same structure. They will overwinter inside structures (in walls, attics, under siding, within voids of overhangs, in basements, and in other sheltered locations. They mate after emerging in the spring. Neither cluster flies nor face flies multiply within structures.

CLUSTER FLY IDENTIFICATION: Adult cluster flies are approximately 3/8 inch long. They are a non-metallic, dark gray. Their thorax is lacking distinct strips ( as found on face, flesh, and house flies), but the thorax may have very small yellowish hairs (usually lacking in older specimens). The abdomen appears to have irregular, but a somewhat horizontal, light to dark pattern. These flies may appear somewhat sluggish.

BIOLOGY: Cluster flies lay their eggs in soil and they hatch in a few day (3 or 4). The cluster fly larvae are parasitic on earthworms. Life cycle, time from egg to adult, is about 30 to 40 days, and there are usually four (4) generations per year.

FACE FLY IDENTIFICATION: Adult face flies are about 1/4 inch long (about the size of a house fly) and are a dark gray color with 4 narrow black longitudinal strips on the thorax dorsum, blackish-gray abdomen.

BIOLOGY: Face flies lay their eggs in fresh, undisturbed, cow manure. The eggs hatch in 10 to 20 hours and there are 3 larval instars which take about 3 or 4 days with the last larval instar traveling away from the manure pile to pupate in the soil. Following approximately 10 days in the pupa the adult face fly emerges. Life cycle, time from egg to adult is about 20 days. Female face flies feed on mucus and secretions around the eyes, nostrils, and mouths of livestock. Male face flies feed on flower nectar.

OVERWINTERING HABITS: Cluster and face flies have been known to co-inhabit (overwinter) in the same structure. When the night time temperatures become cool in the early fall, cluster flies and face flies enter structures to overwinter. Cluster flies have a tendency to infest the same structure year after year, and the same can be said of face flies. Whether its cluster flies or face flies, they enter structures one at a time, and a great number (hundreds or thousands) may enter for the winter! During sunny, warm winter days (45-50 degrees F), some of these flies can become very active: you may find several hundred of them buzzing around a room or window. They are attracted to light. You may think you killed all of them one day only to find just as many, or more, swarming around the following day, or even more the day after that, and then there's next week!

ONE SERVICE TRIP IS NOT GOING TO RESOLVE A CLUSTER FLY PROBLEM! Expect a professional pest control company to charge for each cluster fly/face fly service trip, and due to the nature of this pest and the condition of your house or office building, you may need several service trips (see below)!

WHY DO I HAVE CLUSTER FLY and/or FACE FLY PROBLEMS? WHY ME? There are generally two (2) reasons your house or office building has cluster fly and/or face fly problems: A) faulty construction or B) neglected maintenance.

A) Faulty construction: Cluster flies and face flies enter houses and office buildings through areas the builder did not properly seal, caulk, trim, flash, or screen, including, but not limited to, the following: 1) areas where roofing is or should be flashed and areas where venting in eves or roofing is not adequately sealed and/or screened, 2) areas around window and door framing/trim, 3) cracks and voids in exterior veneer, 4) areas where the exterior trim or siding does not fit properly or is not sealed, 5) areas where exterior siding overhangs the foundation and is not sealed/caulked, 6) poorly crafted windows and sliding doors, and/or 7) areas that have not be properly sealed/caulked where vents or utility lines exit the structure. 8) Sometimes, cluster flies and/or face flies will enter through the space around overhead garage doors and enter attic areas through loosely fitted attic access panels/doors located in the garage ceiling.

It is common for new(er) houses, even the most expensive new(er) houses, to have annual cluster fly problems. The reason is always one or a combination of the above.

B) Neglected maintenance in older houses and buildings: self explanatory.

PROFESSIONAL PEST CONTROL SERVICE IS RECOMMENDED for cluster and face fly infestations. Be advised: insulation within attics and wall voids will hinder pesticide application and limit the effectiveness of the controls that can be provided. In addition to professional pest control service, the property owner should also attend to any needed repairs (see below).

UNLESS THE PROPERTY OWNER FINDS AND PROPERLY REPAIRS THE ACCESS AREAS (see A and B above), S/HE MAY EXPERIENCE CLUSTER FLY AND/OR FACE FLY PROBLEMS EVERY YEAR (SPRING, FALL, AND ON OCCASIONAL WARM, SUNNY WINTER DAYS).

Give Best Exterminators, Inc. a call, if you live or work in the Greater Kansas City Metro (KS & MO) area.

(816) 765-8844

Office Hours: 8:00 AM to 4:30 PM weekdays, except holidays