A source for information on flies
Face Fly Musca
Although face flies are non-biting creatures, their feeding habits make them
troubling to cattle. Face flies feed on the secretions produced by the eyes and noses of large animals. Beyond
irritating cattle, this behavior also can result in the transmission of diseases. Affected animals often hide in
dark places, produce less milk and lose weight. Face flies may also inflict pinkeye upon the animal and can
transmit eye worms to both cattle and horses.
Face fly eggs are yellow, white or translucent in color. Each egg measures
approximately three millimeters in length and 1/2-millimeter wide. Two ridges are located along their sides. When
face flies enter the larval stage, they resemble yellow maggots. Adult face flies measure between six and eight
millimeters in length and appear similar to house flies. Their mouthparts are commonly blunt when compared to other
fly species. Both males and females have gray thoraxes with four dark brown stripes. Abdomen colors vary between
genders: male face flies are brown or orange with black bases and dorsal stripes, while females are primarily black
with orange bases.
Female face flies only lay their eggs in the manure of grass-fed cattle. They
prefer manure that is 10 to 15 minutes old and avoid other feces. Eggs hatch within manure and larvae develop under
a crust of the manure. Upon maturity, face fly larvae crawl into soil close to the manure in order to complete the
pupal stage. After a week or so, adult flies emerge above the soil. Complete life cycle of face flies requires
approximately two weeks.
Medium-sized flies about 1/4-inch in length.
Dark gray; four stripes are present on top of the thorax in front of the wings. Looks identical to a house
This fly is very closely related to the house fly and, in fact, an entomologist is needed to distinguish
between the two species. If “house flies” are suddenly appearing inside a building during the fall, winter, or
spring, then face flies are likely involved. The face flies status as a pest is similar to that of the cluster
fly. These flies have discovered that heated buildings are ideal for surviving the cold of winter, and the face
fly is one such species. As the weather cools in late summer and early fall, the sun warms the southern and
western walls of buildings. The warmth attracts these insects to buildings where they crawl inside cracks and
stay there for the winter. This would be fine, but during warm winter days, some flies “wake up” and end up on
the inside of the building.
Like house flies, face flies breed primarily in fresh animal manure and so are more common in buildings in
rural areas near farms.
The best way to control face flies is by prevention as described below. If it’s too late and they are
already inside, it takes a professional to find and treat the right areas to minimize the numbers of pests seen
inside. If your building has experienced a problem in the past with face flies (or other overwintering pest
species), take the following steps next summer to prevent a recurrence:
- Seal as many cracks and holes on the outside of the building as possible, especially on the south and
west walls where the sun heats the surfaces during the late summer and fall.
- Be sure that all foundation and attic vents (if present) have tight-fitting insect screens. Plug weep
holes in brick veneer buildings with small pieces of screening or wire mesh. Do not permanently seal weep
- Check the soffit vents and any gable vents or turbine vents on the roof.
- Have your Terminix professional treat the outside west and south walls of the building near the eaves.
This treatment should be completed in mid- to late August.
If flies are already inside the building, complete elimination of interior invasions is often not possible.
Treatments may be applied to cracks around window frames and into cracks in walls above false ceilings, but
these may not reach all the voids and spaces in which flies might be waiting out the winter. Sealing cracks
around window frames is helpful in excluding flies from crawling into the building’s interior rooms.