Musca domestica, commonly known as the house fly, is a familiar insect found globally in close association with human environments. These small, grayish-brown flies are members of the Muscidae family and are recognized by their bristly bodies, spongy mouthparts, and compound eyes. They are widespread and can reach high population densities, posing a nuisance.
Life Cycle
The house fly undergoes a complete metamorphosis, progressing through four distinct stages: egg, larva (maggot), pupa, and adult. The entire life cycle can be completed rapidly, often within 7 to 10 days under optimal warm conditions, though it can extend to two months in less favorable environments. This rapid development allows for multiple generations annually.
The cycle begins when a female house fly lays white, oval-shaped eggs, approximately 1.2 mm long, in moist, decaying organic matter such as manure, garbage, or rotting food. A single female can produce several batches, laying between 75 to 150 eggs per batch, totaling up to 500 eggs in her lifetime. These eggs typically hatch into larvae within 8 to 24 hours.
The larval stage, often called maggots, features a cylindrical, legless, and creamy-white body that can grow up to 12 mm long. Maggots feed on the organic material where they hatched, undergoing three growth stages (instars) over 3 to 5 days. Following the larval stage, the maggots seek a drier, cooler location to transform into pupae.
The pupal stage involves the formation of a reddish-brown, oval-shaped casing, known as the puparium, about 8 mm long. Inside this protective casing, the larva transforms into an adult fly, a process that usually takes 3 to 6 days at optimal temperatures, but can take 20 days or more in cooler conditions. Once metamorphosis is complete, the adult house fly emerges, ready to reproduce within 24 to 48 hours. Adults typically live for about 15 to 30 days, surviving longer with suitable food and cooler temperatures.
Disease Transmission
House flies are capable of transmitting a wide range of pathogens, posing a public health concern. The World Health Organization estimates that house flies can transmit at least 65 different diseases.
Flies often feed on decaying organic matter, animal feces, and garbage, picking up bacteria, viruses, and parasites on their bodies. Pathogens can cling to the tiny hairs on their legs, body, and mouthparts. When a fly lands on human food or surfaces, these microorganisms can be transferred.
In addition to physical transfer, house flies also spread pathogens through regurgitation and defecation. When feeding on solid food, a house fly regurgitates stomach contents, including digestive enzymes and accumulated bacteria, onto the food to liquefy it. Bacteria residing in their digestive system can also spread through their feces wherever they land. This behavior increases the risk of contaminating food and cooking utensils, especially when flies gather in kitchens or hover over food.
Common diseases house flies can spread include food poisoning, dysentery, cholera, typhoid fever, salmonella, anthrax, tuberculosis, and eye infections like conjunctivitis. The eggs of parasitic worms can also be transmitted by house flies. Consuming contaminated food or liquids, or touching infected surfaces and then one’s eyes or open wounds, are common ways to contract illness.
Control Measures
Controlling house fly infestations involves a combination of practical measures focused on sanitation, physical barriers, and basic trapping methods. The primary strategy involves eliminating breeding sites and reducing attractants.
Effective sanitation is fundamental. Since flies lay eggs in moist, decaying organic matter, regularly removing and properly disposing of such materials is important. This includes consistently emptying and cleaning garbage cans, ensuring they have tight-fitting lids. Food waste should be placed in sealed plastic bags before disposal, and any spilled feed or organic debris should be promptly cleaned. For areas with animal waste, such as farms, frequent removal (at least twice a week) of wet manure disrupts the fly’s breeding cycle.
Physical barriers are another effective method to prevent flies from entering homes and other structures. Installing and maintaining well-fitted screens on windows and doors is an important step. Sealing cracks around windows and doors can also limit entry points. Air curtains, which create an air barrier, can be used in doorways, particularly in kitchen areas, to deter flies.
Basic trapping methods can help reduce adult fly populations. Sticky fly ribbons or flypaper can be hung in infested areas, ideally within 6 feet of the floor where flies are most active. Ultraviolet light traps can also be effective indoors, placed where they are not visible from outdoors to avoid attracting more insects. For outdoor use, odor-baited traps can be employed, but should be placed some distance from the building due to their foul odor. While insecticide baits are available, they supplement sanitation practices and should be placed in areas inaccessible to children and animals to prevent accidental exposure.