Flies belong to the order Diptera and are characterized by having only one pair of wings. The hind wings are vestigial and represented by two short organs known as halteres that serve to balance the fly during flight. Most commonly encountered flies have large compound eyes and usually three simples eyes. Their mouth parts are of the sponging/lapping/ or piercing/sucking type. Flies develop by complete metamorphosis with life stages of egg, larva, pupa and adults. The key to eliminating fly populations and breaking the life cycle lies with the larval and then the adult stages. The larvae are less mobile and will be breeding in the “source” of the ongoing infestation. Adult flies are short lived and can be controlled using a variety of pest management techniques. The flies that infest structures may be discussed in five separate groups: filth flies, small flies, overwintering flies, biting flies and gnats and midges. These various groups of flies contain species that have similar habits rather than those that are closely related taxonomically. 

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Types of Flies

House Fly
House Fly
The house fly is one of the most familiar of all insects. The house fly is 1/6 to 1/4 inch in length, with the female usually larger than the male. The size of both sexes depends to so me extent on the availability of food in the larval stage and whether the abdomen is distended with food at the time of examination. The thorax bears four narrow black stripes and a sharp upward bend is present in the fourth longitudinal wing vein. The sexes can be readily separated by noting the space between the eyes, which in females is almost twice as broad as in males or by applying pressure to the abdomen, which results in the protrusion of an ovipositor in the case of the female. The house fly passes through four stages in its life cycle: egg, larva or maggot, pupa and adult. The females, usually in clusters of 20 to 50, can be seen depositing their eggs on a suitable breeding medium. The white eggs, about 1 mm in length, are laid singly but pile up in small masses. During the females’ lifetime, she may lay five or six batches of 75 to 150 eggs at intervals of several days between each batch. All in all, she may deposit from 350 to 900 eggs. Ordinarily, the house fly commences to lay her eggs from four to 12 days after emerging from the pupal case and tends to favor moist materials for egg deposition. The white, legless maggots emerge from the eggs in warm weather within eight to 20 hours, and they immediately begin feeding. Completion of the larval stage requires three to seven days at temperatures of 70 degrees Fahrenheit to 90 degrees Fahrenheit, although six to eight weeks may be required at lower temperatures. House flies feed on fecal material, vomit, and sputum, after which it might alight on human food. Under microscopic examination, it can e understood why flies carry pathogens such as bacteria and other disease causing organisms. The fine hairs covering a fly’s body may harbor disease pathogens, and that combined with their ability to quickly fly distances means flies have little trouble spreading bacteria and pathogens. House flies have been shown to carry the disease organisms causing typhoid fever, cholera, summer diarrhea, dystery, tuberculosis, anthrax and ophthalmia as well as parasitic worms. 
Fruit flies are small flies that can pass through ordinary screening and are common in homes, restaurants, fruit markets, canneries, and similar places. The fruit fly is attracted to human and an imal excrement and also will feed on fruits and uncooked food, and thus may act as a vector of disease. Fruit flies are considered a significant pest when found in food producing or food handling facilities. It breeds in and feeds on ripened fruits and vegetables, as well as mo ist, decaying, organic matter. Because it frequents such unsanitary areas, it could potentially carry disease causing bacteria into food products. Fruit fly larvae living in fruit which is eaten can cause intestinal discomfort and diarrhea. The adult fruit fly is approximately 1/8 inch long, including the wings and has bright red eyes and a tan colored head and thorax, with a blackish abdomen, the under surface of which is grayish. The fruit fly is cosmopolitan in distribution and is very common wherever fruit and materials of like nature are permitted to rot and ferment. The eggs, which are difficult to see with the naked eye, are deposited near the surface of the fermenting material. A pair of filaments attached to the eggs protrude above the surface of the liquid allowing the larvae to breathe. The larvae usually emerge from the eggs about one to two days after deposition. Feeding occurs near the surface of the fermenting mass. The average length of the larval period is from five to six days. The adults mate more than once and deposit an average of approximately 500 eggs. The entire life cycle may be completed in as few as eight days. 
Fruit Fly
Phorid Fly
Phorid flies are small flies up to 1/8 inch in length including the wings. They are usually tan to dark brown in color. A key characteristic is the severe arch, or humpbacked shape, of its thorax compared with its small head, thus giving it the nickname “humpbacked fly”. The phorid fly lacks the red eyes of the fruit fly-the fly with which it is most often confused. The wings of the phorid fly also have two heavily sclerotized veins at the top of the wing, and the remaining veins are very weak and are not joined by cross veins. Adult flies have the peculiar habit of running rapidly along surfaces instead of immediately flying when disturbed. Phorid flies are found throughout the world and are a serious pest in all types of food handling facilities. They primarily breed in and feed on moist, decaying organic matter and probably have the greatest variety of potential breeding sites of any type of fly. Trash containers that are not cleaned regularly are a good source for phorid flies. Trash containers that become breeding sources for flies are usually those that are not lined with bags. Phorid flies are a particular concern in hospitals and other health care facilities. Phorid fly larvae have been found in open wounds of patients and in laboratory petri dishes, resulting in contamination due to bacteria that might be found on their bodies. The tiny eggs are deposited on or near the surface of decaying organic matter. The female will deposit about 20 eggs at a time. The larvae emerge within 24 hours and feed for eight to 16 days depending on t he food source and temperature. The larvae then crawl to a drier spot to pupate. Under ideal conditions the life cycle from egg to adult can be completed as quickly as 14 days, but may take as long as 37 days. 
Moth flies (also known as drain flies because they often breed in drains) are at times annoying in hoes, apparently appearing mysteriously from sinks and bathtub drains. Moreover, they may breed in tremendous numbers in sewage-filter plants and then be carried by the wind to nearby buildings where they penetrate through ordinary fly screening. The drain fly is common in the eastern United States. This species is 1/13 inch long with a light tan colored body and lighter wings that are faintly mottled with black and white. The body and wings are densely covered with long hairs which give the fly a moth like appearance, hence the name “moth fly”. The antennae are 12 segmented, each segment having a bulbous swelling with a whorl of long hairs. 
Drain Fly
brown house Fly
Cluster Fly
The cluster fly is widely distributed throughout Europe, Canada and the United States, except for the states bordering the Gulf of Mexico. It enters houses in the fall, one at a time. They may collect together like a swarm of bees. This insect is slightly larger than the house fly and has a nonmetallic, dark gray color. The thorax is without distinct stripes but has characteristic golden hairs. The dark gray abdomen has irregular lighter patches. The wings overlap at the tips when not in use and the sharp bend in t he longitudinal vein of the wing if characteristic. When crushed, this fly has an odor like buckwheat honey. Few insects give the homeowners the creeps as do these large sluggish flies, appearing one by one in late fall or during the winter when the weather warms. The eggs are laid singly in cracks in the soil. During the summer, the eggs hatch in three days, and the emerging maggots can penetrate practically any part of an earthworm. The larval stage may last from 13 to 22 days, and the pupal stage from 11 to 14 days, with a total development period of 27 to 39 days. There are four generations during the summer.