House Fly

houseflyAlthough the house fly is one of the most familiar of all insects, the individual who can separate it from the other common flies is rare. 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 is dependent to some extent on the availability of food in the larval stage and whether the abdomen is distended with food. The thorax bears four narrow black stripes and there is a sharp upward bend in the fourth longitudinal 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.

This insect is cosmopolitan in distribution and is called the house fly because it is very often the fly that occurs most commonly in the home. Howard (1900) collected flies in buildings in various parts of the United States and 98 percent of them were house flies, Musca domestica. With the advent of the “horseless carriage,” the house fly lost some of its preeminence as a household pest, although it is still very important, especially in rural areas.

There is a difference of opinion on what is the most important fly in and around homes and other buildings. This difference is evidently caused by special environmental conditions favoring certain species of flies. DeLong and Boush (1952) fogged supermarkets throughout Ohio and made a survey of the species of flies by the spray.

They found the house fly to account for 28 percent of the flies, whereas the greenbottle fly, accounted for 66.1 percent, and the black blowfly, for 5 percent. (For more info on these flies click on the arrow key at the bottom of this page and look for the section “Flies and Mosquitoes”) Food of the House Fly.

Fermenting, fresh horse manure is a favorite breeding place of the house fly. This manure must be less than one day old to be attractive to the egg-laying adult. However, Leikina (1942) showed the larvae of the house fly develop best in human and pig manure and not so well in horse manure. According to Coffey (1951), who made a study of fly breeding substances in Texas, the most important breeding places in descending order are horse manure, human excreta (privies), cow manure, fermenting vegetable refuse and kitchen garbage.

Howell (1975) found swine barns, horse barns, sheep barns, cattle barns and poultry buildings in descending order had the most house flies. The sanitation in each barn was approximately equal. Yates et al. (1952) noted house flies are attracted to the ammonia emanating from horse manure.

Chapman (1944) observed the house fly to complete its development in a mattress wetted with human urine. Miller and Mallis (1945) found flies were causing much annoyance in the vicinity of a dump filled with incinerated garbage, particularly in citrus rind and pulp that was not completely burned. The flies bred in incinarated garbage if it was fresh and wet, but not in incinarated garbage that was scattered or two to 10 months old. Sawicki and Holbrook (1961) made a survey of rearing methods for house flies. The author has found house flies breeding in rotting vegetables stored on a shelf in a hotel kitchen.

Life Cycle. 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 suitable material. The white eggs, which are about 1 mm long, are laid singly but pile up in small masses. The female deposits from 75 to 150 eggs and during her lifetime she may lay five or six batches at intervals of several days between each batch. All in all, she may deposit from 350 to 900 eggs, and one female has been known to deposit 2,387 in 21 batches (Dunn, 1923). 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. Eggs that become too dry during the incubation period will fail to hatch.

The white, footless maggots emerge from the eggs in warm weather in from eight to 20 hours and they immediately begin feeding. Completion of the larval stage requires three to seven days at temperatures of 70 to 90 degrees F, although six to eight weeks may be required at lower temperatures. The larvae undergoes three instars. The full-grown maggot has a greasy, cream-colored appearance and is 7 to 10 mm long. It can be separated from the blowfly’s maggot with which it may otherwise be confused by the sinuous slits in the posterior spiracles.

When the larva becomes fully grown, it seeks a dry, cool place to pupate and migrates from its food source to the soil beneath nearby boards, stones, etc. Barber (1919) observed house fly larvae to migrate 150 feet to a sewage manhole rather than pupate in the warm soil beneath a manure pile. The larvae may be in the prepupal or migrating stage for three to four days.

The pupa is the stage wherein the mature maggot transforms into the adult. It is passed in a pupal case formed from the last larval skin which varies in color as the pupa ages from yellow, red, brown, to black. Ordinarily, the size of the maggot determines the size of the pupa which in turn determines the size of the adult fly. Moreland and Mcleod (1957) noted that the smaller pupae are mostly male while the larger ones are mostly female. Arnold Mallis noted that pupae reared in the laboratory of Gulf Research and Development Co. weighed 18 to 24 mg with an average weight of 21 mg, and 1,350 pupae weighed about 1 ounce. The pupa transforms into an adult in three days to four weeks or longer, depending primarily on temperature and humidity.

The emerging fly escapes from the pupal case through the use of an alternately swelling and shrinking sac or ptilinum on the front of its head which it uses like a pneumatic hammer. Bucher et al. (1948) noted at about 80 degrees F, (about one hour is required after emergence for expansion of the wings and general hardening of the body. At this temperature the adults remain relatively quiescent for about the first four hours. Normal activity is reached in about 15 hours.” During the warm weather of summer, when conditions are generally optimum for the development of the house fly, it may require as little as six days to complete the cycle from egg to adult, and there may be as many as 10 to 12 generations in one summer.

Simanton and Miller (1938), while making a study of the house fly relative to the Peet-Grady method of testing, found that in the laboratory at 80 degrees F and relative humidity 55 percent, copulation begins on the second day after emergence and almost all the females are fertilized by the end of the third day. It is heaviest from the third through the ninth day and then gradually tapers off. Patterson (1957) observed the house fly to mate twice; once when she was three days old and again when she was seven to 10 days of age.

The House Fly and Disease. Although the house fly is often an unbearable nuisance, we are primarily concerned with it as a carrier of disease organisms. The house fly feeds on fecal material, vomit and sputum, after which it might alight on human food. It is very well adapted by both structure and behavior for the transmission of disease. Its body is covered with fine hairs and bristles which readily pick up dirty particles. At the base of each of the two claws at the end of each leg there is a cushion-like structure, the pulvillus, which is covered with glandular hairs. The sticky secretions also enable the fly to climb vertical surfaces and to walk upside down. The house fly excretes and regurgitates wherever it comes to rest. Moreover, flies commonly fall into liquid foods and contaminate them in this fashion. According to Barber and Starnes (1949), fly regurgitation “is a process of digestion during which the food is brought up from the crop bit by bit and is mixed with saliva before being passed on to the digestive tract.”

House flies have been shown to carry the disease organisms causing typhoid fever, cholera, summer diarrhea, dysentery, tuberculosis, anthrax, ophthalmia, etc., as well as parasitic worms. Watt and Lindsay (1948) noted that fly control definitely reduced infestion, disease and death due to diarrhea in Texas. Frison (1925) recorded the regurgitation of house fly larvae by a sick boy. Greenberg (1967) prepared an interesting article on house flies as vectors of Salmonella bacteria which are responsible for food poisoning and gastric infections. Experimental work has demonstrated the presence of the virus of poliomyelitis in or on flies trapped in epidemic areas, and the flies in homes of polio patients can contaminate food with the virus. Power and Melnick (1945), in studying the fly population in an epidemic poliomyelitis area, showed the house fly was not the dominant fly and that flies of other genera such as Phaenicia sericata were more common.