Filth flies are insects that breed and feed in decaying organic matter, refuse, or animal excrement. Their life cycle and feeding habits bring them into constant contact with environments rich in disease-causing microorganisms. Recognized as a serious public health concern, these flies act as carriers, transferring pathogens from contaminated sites to human food and surfaces. Understanding their behavior is crucial for mitigating the risks they introduce.
Identifying Common Filth Fly Species
The flies most commonly encountered can be distinguished by their physical appearance and preferred breeding grounds. The common house fly (Musca domestica) is perhaps the most familiar, appearing dull gray and measuring about a quarter of an inch long. House flies are prolific breeders, favoring decaying vegetable waste, animal manure, and garbage containers as egg-laying sites.
Blow flies, often called bottle flies, are easily identified by their distinct metallic sheen, typically appearing green, blue, or copper-colored. These flies are drawn to carrion and decaying meat, where their larvae develop quickly. Stable flies (Stomoxys calcitrans) resemble house flies but possess a pointed, bayonet-like proboscis used for biting. The stable fly feeds on blood, and its larvae develop in moist, decaying organic materials like wet straw, spilled animal feed, or drying lawn clippings.
Mechanisms of Pathogen Transmission
Filth flies move harmful microbes because their bodies and feeding behaviors are adapted to transport contamination. The primary route is mechanical transmission, where pathogens adhere to the fly’s external structures. Their legs, feet, and entire bodies are covered in fine hairs and sticky pads that readily pick up bacteria, viruses, and parasite eggs from feces, garbage, and sewage. These contaminants are then deposited directly onto food or food preparation surfaces when the fly lands.
Another method of contamination involves the fly’s unique feeding process, which requires the liquefaction of solid food. Since flies cannot chew, they first regurgitate digestive fluids, including contents from their crop, onto the food source to dissolve it. This action creates a contaminated “vomit spot” before the fly sucks up the resulting liquid, transferring microbes held within its digestive system to the food.
Flies also contaminate surfaces through fecal droppings left behind while they feed or rest. Pathogens ingested from contaminated sources can survive passage through the fly’s gut and are then excreted in these minute waste spots. This combination of mechanical transfer, regurgitation, and defecation allows flies to spread numerous disease-causing organisms. Common pathogens linked to fly transmission include E. coli, Salmonella, and organisms that cause dysentery, food poisoning, and cholera.
Integrated Fly Management Strategies
Effective control of filth flies relies on an integrated approach that focuses on eliminating breeding sources and preventing access to human environments. Source reduction through sanitation is the most important preventive measure, as flies cannot reproduce without decaying organic matter. All garbage should be stored in tightly sealed containers with lids and emptied frequently, especially during warmer months.
Pet waste must be cleaned up promptly, and areas prone to moisture, such as leaky plumbing or wet animal bedding, should be dried or eliminated. Since many flies breed in moist debris, ensuring that floor drains, especially in food preparation areas, are regularly cleaned of organic buildup helps prevent larval development.
Physical exclusion creates a barrier to keep adult flies out of buildings. This involves installing and maintaining screens on all windows and vents, ideally with a mesh density of at least 18 squares per inch. Gaps around doors, utility lines, and air conditioning units should be sealed to deny flies easy entry points.
Supplemental methods, such as traps and lures, can help reduce adult fly populations. Simple traps utilizing attractants or sticky surfaces, like fly paper and ribbons, are non-chemical options suitable for public areas. Ultraviolet light traps can also be installed in sensitive areas to capture flying adults. Chemical control, such as residual sprays or baits, should be used judiciously and often requires professional application when sanitation and exclusion are insufficient.