Egg -- White and about 1 mm long, each egg is elongate with bluntly rounded ends. Eggs occur in clusters of about 100.
Larva -- This smooth, nearly white maggot has a pointed head and no appendages. It develops through 3 instars and may be as long as 13 mm when mature. Two spiracles which are slit-like in early instars and resemble a pair of eyes in a mature larva occur on the tail end. Second and third instar larvae also have spiracles near the head each with six or seven tiny dots.
Pupa -- A house fly pupa develops within a dark brown puparium (hardened skin of a last larval instar) a little over 6 mm long. The puparium has rounded ends and increases slightly in diameter from front to rear.
Feeding Habits -- House flies feed on a wide range of organic matter including feces and many types of liquids.
Damage -- Flies constitute a health hazard as well as an annoyance. As they feed and breed in manure and garbage, these insects are likely to pick up disease-causing organisms. Such flies contaminate human food by crawling on the surface and depositing feces (dark spots) and regurgitated liquid (straw-colored spots). Di seases which have been carried by house flies include typhoid fever, tuberculosis, dysentery, polio, anthrax, diarrhea, yaws, cholera, conjunctivitis, trachoma, tapeworm, hookworm, and pinworm. House flies have been implicated in the spread of over 30 bacterial and protozoan diseases. Fortunately, house flies do not transmit many of these diseases with great frequency.
Life History -- Adult house flies live 2 to 4 weeks in summer and even longer in cool weather. Each female deposits 4 to 6 batches of 75 to 150 eggs on moist animal manure or garbage. Larvae hatch from the eggs in 8 to 24 hours. These maggots feed in decaying organic matter for about 5 to 7 days. If the weather is cold, food is scarce or the medium dry, larval development may require 2 weeks or more.
The pupal period lasts 3 to 6 days in summer but during winter may continue several weeks up to 5 months. At the end of this time, a new generation of flies emerges. Four to 8 days after mating, females begin laying eggs and the cycle is repeated.
In summer, a new generation can be produced every 8 to 14 days, but under unfavorable conditions as many as 20 days may be necessary. Ten to 12 annual generations are common. House flies usually overwinter in the immature stages, primarily as prepupae.
In poultry houses, manure should be kept dry. Manure should not be removed during the warm months in order to preserve predaceous mites which feed on house fly eggs and larvae. Pesticides should be applied for house flies as needed but not for house fly larvae.