All flying insects, whether it be flies, bees, indian meal moths, etc., come from a source. The source can be decaying garbage or even old, rotting food or leaking water.
Once the sources are eliminated and steps are taken to secure possible pest entry points, the infestations will be gone.
The flies that infest structures may be discussed in five separate groups: filth flies, small flies, overwintering flies, biting flies and gnats and midges. Of these groups, only certain types of flies in the small fly group will be found regularly breeding inside structures. The other types of flies breed outside and are attracted to buildings by food odors, temperature gradients in the air, and exterior lighting. These factors affect how different fly situations will be handled.
The habits of filth flies favor the spread of bacteria and other disease-causing organisms. Filth flies often feed and lay eggs on garbage, manure and carrion before contaminating human foods and food preparation surfaces by landing on them. When feeding, house flies regurgitate their stomach contents onto food to liquefy it before ingesting it. They also may contaminate food and surfaces by defecating on them.
Sanitation is key to managing “filth” flies.
Large Filth Flies
House Fly house fly
Adults are 1/8″ to 1/4″ (4-8mm) long and are gray with four dark stripes lengthwise down the thorax. Mature larvae (maggots) are 1/4″ to 3/8″ (7-10mm) long and creamy white; their bodies taper toward the head. House flies are attracted to a wide variety of food sources, from fresh food to excrement. Adult flies have spongy mouth parts allowing them to ingest only liquid foods. Regurgitation is necessary on solid foods to liquefy them for consumption.
House flies are abundant and filthy. They have been found to carry over 100 different human pathogens due to their habits of walking, vomiting, and feeding in unsanitary places as well as on human food. Additionally, house flies are a nuisance to humans and domestic animals.
Bottle, Blow and Flesh Flies
Bottle and blow flies are 1/8″ to 5/8″ (4-16mm) long as adults and 3/8″ – 7/8″ long as mature larvae. Bottle and blow flies are often a bright metallic green, blue or bronze, but some species are black. Flesh flies are 1/4″ -1/2″ long as adults and 3/8″ to 3/4″ (9-20 mm) long as mature larvae. Flesh flies are dull gray to black with three longitudinal strips down the thorax, and reddish eyes. Larvae of both types of flies are creamy white; their bodies taper at the head. All of these flies develop in excrement, sewage, decaying flesh or carrion, and in similar substances.
Bottle, blow, and flesh flies may transmit many serious diseases to people through food borne illness. These flies are also a nuisance to humans and domestic animals. Large numbers of these flies indoors usually indicates the presence of a dead animal such as a mouse or bird inside the structure.
Small Filth Flies
Fruit Flies (Vinegar Flies) fruit fly
Also known as vinegar flies, small fruit flies are 1/8″ (3 mm) long and are yellow-brown to dull, dark brown with red or orange eyes. They lay eggs in fermenting or rotting fruits, vegetables and grains as well as in wet mops, garbage and recycling bins, and any fermenting substance or liquid.
Small fruit flies are a nuisance pest and commonly encountered indoors. They are abundant outdoors during warm weather and are difficult to exclude from structures with regular window screens, which they will crawl through.
Sanitation is key to fruit fly management. As with most flying insect infestations, the larval breeding source needs to be located and eliminated for long term success. Existing fruit flies can then be controlled with traps and vacuuming.
Fungus Gnats fungus gnat
1/32″ to 7/16″ (1-11 mm) in length, fungus gnats are dark, delicate, tiny flies that are attracted to light on computer screens or in windows. These flies feed on fungi and moist decaying matter found in rich soils. Indoor infestations can be associated with pigeon dropping or over-watered potted plants where fungi develops. In some cases, they may be breeding in moist areas associated with leaks, peeling paint, or rotting wood. Fungus gnats are typically an indication of mold or rot in the structure.
When removing pigeon or bat droppings, take care to wet the area first with disinfectant to kill disease-causing organisms that could potentially be present in the droppings.
Phorid Flies phorid fly
Also known as humpbacked flies because of their arched thorax, phorids are tiny, dark-colored flies. The larvae feed on a wide variety of decomposing organic (of plant or animal origin) debris. If suitable materials are present, huge populations of phorid flies can build up quickly. Sources of infestation include liquefied garbage, sewage and carrion, often hidden in places difficult to inspect and access.
Moth or Drain Fly drain fly
1/16″ to 1/4″ (2-5mm) in length, these flies resemble tiny moths due to their fuzzy, heart-shaped wings, and long antennae. Their color ranges from yellow to gray or brown to black. Larvae are thin and longer than adults with transverse dark bands across the body. Larvae and pupae inhabit the gelatinous layer that accumulates in sink and floor drains; adults are usually spotted resting on walls near drains. They are common outdoors and easily become established indoors. Moth/drain flies are primarily a nuisance that indicate poor drain maintenance.
To eliminate infestations, mechanical cleaning with a wire brush is recommended over bleach (which does not work) and cleaners that do not remove the layer of scum inside drains. Specialized enzymatic cleaners that remove drain slime are recommended to manage moth flies. After the source is targeted, existing drain flies can be eliminated through vacuuming and trapping. Cracks and crevices should also be sealed to prevent organic matter accumulation, and clutter should be removed to allow for proper ongoing inspections and cleaning.
Cluster Fly cluster fly
Cluster flies are dull dark gray with golden hairs on the thorax and measure about 3/8″ long. Abdomens have irregular light and dark patches. Cluster fly larvae are parasites of earthworms in the soil. These flies are found indoors in colder months and appear very sluggish as they fly around a room. They are attracted to windows and may accumulate in enormous numbers. They are harmless and are not a filth-carrying fly.
During most of the year, cluster flies are not a problem in structures. It is only when fall approaches that they begin to enter structures in large numbers. Cluster flies begin to seek protected overwintering sites in late August and September. Adults may fly more than a mile to a site that offers shelter. They are attracted to light colored tall buildings and will invade attics or wall voids on the sunny side of the house or building and become active on warm late-winter days. The walls on the south and west sides are the ones usually affected because the late summer sun shines most on these sides.
It is impossible to eliminate cluster flies outside, so you’ll need to exclude them. The best and most effective method of controlling cluster flies in buildings is to prevent them from entering the building in the first place. Structural repair, caulking and fixing all window and door screens will help prevent pest entry. If clusters of flies are found on open surfaces in attics, crawlspaces, or false ceilings, the best approach would be to simply vacuum the flies from these surfaces. For extreme cases, residual pesticides may be used if required and should be applied only to non-human contact surfaces where flies are entering the structure. As always with flying pests, cleaning and sealing cracks and crevices and all other entry points is the most effective way to eliminate the cluster fly.