Quick Facts...
- Several species of flies enter homes in Colorado. Most are mere nuisance
problems.
- Cluster flies, and some other blow flies or face flies are found during
fall and winter. They use homes for shelter from the cold but do not
reproduce at this time.
- Blow flies or house flies are found in the home during summer. These
flies develop in garbage, manure or other animal materials.
- The best way to control fly problems in a home is to exclude them
by screening.
- Insecticides can supplement other controls for some flies. Apply them
to fly resting areas, away from food.
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Figure 1: House fly life stages.
(Photo courtesy Clemson University.) |
Several species of flies commonly enter Colorado homes. Most are merely
nuisance pests. Others are important because they can transmit diseases.
House flies, face flies and blow flies develop in manure, carrion, and
garbage and are commonly contaminated with disease-causing bacteria, including
those associated with food poisoning.
The most commonly observed stage of a fly is the winged, adult stage. The immature stage is a pale, legless maggot. When full grown, maggots wander from the breeding site in search of a place to pupate. Many flies complete development (egg, larva, pupa, and adult) in a short period, seven to 14 days, and produce many generations during a typical season.
Although flies most often are a nuisance during the warm season, indoor
overwintering is very common with cluster flies.
Common Colorado Flies
Blow Fly
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| Figure 2: Blow fly (Greenbottle fly). |
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| Figure 3: Black blow fly. |
Blow flies are fairly large, metallic green, gray, blue or black flies
found throughout the state. Common species include the greenbottle flies
(Lucilia spp.), black blow fly (Phormia regina), and various
Calliphora species. These flies tend to be the most common flies found
in and around homes during the warmer months. Adults also may winter behind
walls and occasionally are observed within homes during cooler months,
but are not reproducing at this time.
The blow flies are scavengers, particularly of animal-based materials.
The breed commonly in livestock manure or pet waste and fresh carrion.
The presence of large numbers of blow flies within a home may be due
to several reasons. Large numbers of them sometimes occur when a dead
animal - usually a mouse or squirrel - dies within the home. The presence
of the flies are often preceded by observations of migrating maggots.
Although such occurrences are unpleasant, they are usually short-live
and self-limiting, as the insects are only capable of breeding on freshly
killed animals. Blow flies sometimes are attracted to gas leaks. Also,
the presence of blow flies may just result from their seeking shelter,
as the cool shade of homes provides favored resting sites for flies that
may otherwise be developing outdoors.
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| Figure 4: Blow fly (Calliphora). |
House Fly
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| Figure 5: House fly. |
House flies are the best known of the house-infesting flies but generally
not abundant in Colorado. House flies generally are gray, with the thorax
marked with broad dark stripes. Most often there is some yellow coloring
along the sides.
House flies usually are found where humans are present. Larvae commonly develop in or near man-made sources of food and can be found in garbage, animal waste, culled fruits and vegetables, and spilled animal feed. The adult flies feed on a wide range of liquid waste but can eat solid foods, such as sugar. To digest solid foods, house flies liquefy food by regurgitating it. Because of this habit, house flies can pose serious health threats by mechanically transmitting disease organisms. During mild winters, house flies may fly and breed continuously, as temperatures permit.
Little House Fly
Little house flies are smaller than house and face flies but similar
in appearance. Indoors, they fly for long periods and rarely rest. The
adult flies lay eggs in decaying organic matter, particularly very moist
manure, where the maggot-stage larvae feed.
Cluster Fly
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| Figure 6: Cluster fly. |
Cluster flies are, by far, the most common fly found in homes during the cool
months. They can sometimes be serious nuisance problems, particularly
in taller buildings where they tend to concentrate on upper stories on
the south and west sides. Cluster flies are moderate sized, generally
dark gray and are distinguishable by the presence of golden hairs on areas
of the thorax.
Cluster flies are actually a type of blow fly, but have very different
habits. They develop as parasites of earthworms and are not associated
with garbage, animal wastes, or other materials that provide breeding
of the various 'filth flies'. In spring and summer the adult flies lay
eggs in soil and the maggots move to and develop within earthworms.
Flies that are present in late summer seek winter shelter and they survive
winters as a semi-dormant adult fly. They may be seen sunning themselves
on sun-exposed sides of buildings during warm periods and later infiltrate
cracks in the building. In the process of seeking sheltering sites within
the building they tend to migrate upwards, and thus are found most abundantly
in upper floors of buildings. During the cool season some flies may inadvertently
become active and fly lazily within the living spaces. However, cluster
flies do not feed nor reproduce within buildings.
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| Figure 7: Fungus gnat. |
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| Figure 8: Vinegar flies (Drosophila). |
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| Figure 9: Humpbacked flies. |
Picture-Wing Fly
Maggots of picture-wing flies develop by feeding on decaying plant material
during the growing season. In late summer, they seek overwintering shelter
and are a common invader of homes. They are harmless and do not reproduce
indoors.
Fungus Gnat
Fungus gnats are small, dark flies most often found collecting around
windows during fall and winter. Fungus gnats can be found indoors infesting
potting mixes used for houseplants or hopping across the soil surface.
High organic matter plant mixtures and organic fertilizers, such as fish
emulsion, encourage fungus gnat development. Overwatering, a common problem
during fall and winter, increases fungi and fungus gnat development. Fungus
gnats can reproduce on indoor plants and cause little if any damage. They
also occur outdoors where they breed in mushrooms and other decaying plant
materials.
Pomace or Vinegar Fly
Pomace or vinegar flies are among the smallest flies found in homes.
They usually are light brown and may be marked with bright red eyes. These
small "fruit flies" most often are found hovering around overly ripe fruit.
Fermenting materials, such as leftover beer or soft drinks, also are a
favorite food. Populations tend to be greatest in late summer and early
fall as they infest fruits during the harvest season.
Drain Fly
Drain flies, also known as moth flies, are occasional problems in homes.
These small, moth-like flies sometimes emerge from drains of sinks, particularly
in spring. Drain fly maggots develop by feeding on bacteria and organic
materials that can colonize the linings of drains. Large numbers of the
flies can be produced where there is a problem with broken or leaking
drain pipes.
Fly Control
Sanitation practices that remove breeding areas are fundamental to the control of filth-breeding flies, such as house flies and blow flies. Remove or cover garbage and clean spilled animal feed and manure. Face flies, which typically develop in pasture lands, and cluster flies (earthworm parasites) often are difficult to control by breeding area management.
To control fungus gnats, correct the conditions of the breeding area. Allow the soil to dry thoroughly between watering and eliminate decomposing plant materials. This reduces the amount of fungi where fungus gnats breed.
Vinegar flies are best controlled by removing breeding sites. Discard overripe fruit and wash bottles and cans during recycling.
Drain flies, which develop on the gelatin-like coating that forms in drains and pipes, often are eliminated by correcting cracks or leaks in pipes that allow seepage or serve as breeding areas.
Screening and other exclusion techniques can be an important management tool for several types of indoor fly problems. Caulk or cover all openings into a home to prevent flies from entering. Do so before flies enter buildings. For example, cluster flies rarely are found indoors until late winter and spring but typically enter buildings during late August and September.
Use insecticides only as a supplement to other controls. Serious problems exist with insecticide-resistant flies and many fly populations are now difficult to control with insecticides.
Spot treatments applied to areas of high fly activity are most efficient.
For example, flies that tend to rest in dark corners can be controlled
by applications to these areas. For cluster flies, treat upper stories
of building exteriors immediately before the flies move indoors for overwintering.
Permethrin is currently the most common insecticide used for fly control
and is widely available.
Where fungus gnats are a problem, insecticides can supplement the cultural control of reduced watering. Houseplant aerosols that contain pyrethrins or resmethrin, applied at two- to three-day intervals for three to four weeks, should eliminate most of the adult fungus gnats.
Several types of traps for flies also are available and can supplement other
controls. Fly paper and electrocution light traps can kill flies but are
effective only in areas where exclusion and sanitation efforts have already
reduced the fly populations to low numbers.
Various food-based traps also are for sale. These traps often contain
a protein and/or sugar-based bait, sometimes with the addition of a pheromone
(sex attractant) used by flies. As with other traps, they can supplement
other controls such as sanitation and exclusion. These traps are effective
for species that breed on carrion and garbage such as house flies and
blow flies.
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