Blow flies in the home: how to identify and get rid of these pests
Blow flies, known for their use in maggot therapy and forensic analyses in cases of homicide, may suddenly appear in the home. They look somewhat like house flies, but are fairly large (six to 14 millimetres long) and generally have a metallic sheen to their bodies. They congregate around windows and produce a loud buzzing sound. They do not bite.
Two types of blow flies commonly invade homes: the black blow fly and green-bottle fly. The black blow fly has a dark, olive-green body, whereas the body of the green-bottle fly is coppery green.
Blow flies generally breed in fresh animal carcasses and decomposing organic matter, like garbage, animal manure, and decaying plant material. Full-grown maggots stop feeding and often crawl away and pupate in dark, secluded places. Homeowners sometimes encounter these maggots or pupae but they might be unaware of the problem. Life cycle of a fly is described in my article on cluster flies.
A large number of blow flies may occur in the home due to a variety of reasons
• An animal dies within the home. Dead rodents in walls or in forgotten traps can lead to flies in the home. A squirrel, bird, or raccoon that dies in the chimney or attic can also be source of flies.
• Garbage accumulates for too long. Flies can lay eggs in meat and vegetable scraps in trash cans and can go through an entire generation in less than a week.
• A leak in sewer pipes may result in sudden appearance of blow flies.
• Adult flies sometimes are attracted to gas leaks. Also, the presence of flies may just result from their seeking shelter to spend the winter indoors; they may not reproduce during this time.
Dealing with blow flies
• Find and remove the dead animal. Sometimes it is impractical to do so especially when carcass is inside the wall. Before getting out the wrecking tools, it is helpful to know that blow fly occurrences, although unpleasant, are usually short-lived and self-limiting, as the insects are only capable of breeding on freshly killed animals.
• Tightly seal garbage containers and remove animal (particularly dog) manure from areas around the home. Check window and door screens and sewer pipes for damage.
• Vacuum up adult flies, maggots, and pupae in sight for couple days, and after some time the fly infestation should go away.
• Devices to trap the flies are also offered on the market. These traps attach to a windowpane where flies are a problem and contain a powder (nontoxic) that works like quicksand in trapping the insects that fall in.
• For current chemical control options, consult your local pest control representative. Follow closely the directions and cautions on the label.
Rana Sarfraz is an entomologist and ecologist currently working at the University of British Columbia.