Nuisance Flies

House Fly. ©Clemson University - USDA Cooperative Extension Slide Series,

House Fly.
©Clemson University – USDA Cooperative Extension Slide Series,

There are several types of flies that may be a nuisance around your home. Flies may be more than just a bother, since many breed, feed, or live in our food or in unclean sites such as in manure, garbage, and dead animals. In nature their behavior is important in breaking down decaying matter, but around humans, flies may spread germs to people, food, and eating utensils. This may cause people to be sick. Changing the conditions that help flies breed and survive can help eliminate them. The information provided here will help you understand how to identify the flies that bother you, the conditions that make them successful, and some ways to control them.

Most insects have four wings, but flies have only two. In place of the second pair of wings, are small knob-like structures used for balance. Many flies have a very short life cycle because they often breed in unstable environments. If their life cycle was too long, their environment might disappear before they could complete development.

Though all flies can live outside, you can think of nuisance flies as being in two groups two groups – indoor breeders and outdoor breeders. Examples of indoor breeders are fruit flies (vinegar flies) and fungus gnats. Examples of outdoor breeders are house flies, blow flies, and bottle flies.

Indoor breeders

Fruit fly adults are only 1/8 inch with tan bodies, and bright red eyes. Fruit flies lay their eggs on the surface of fermenting fruit or organic matter. Within two days the eggs hatch and by the end of eight days new adults can be found. If eaten, fruit fly larvae may cause stomach distress or illness, especially, if the breeding site is contaminated. Sometimes breeding sites may be difficult to detect such as with damp mops that ferment due to food particles that were never rinsed off, or boxes of unrinsed drink cans waiting for recycling.

Not very much is known about fungus gnats. Adults range in size from 1/16 to 1/4 inch depending on species. All types have long, thin wings and legs, and most are black in color. These may be difficult to identify without the help of an expert. Usually when fungus gnats are found indoors, they are associated with wet soil in potted plants, atriums in larger buildings, or moisture from leaks in walls and ceilings.  Most often they feed on fungus found in these sites. While they are harmless, their numbers can be annoying and they can carry germs into clean environments.

Outdoor breeders

House fly young develop in very unclean places like fresh manure or garbage. The adults feed at these sites too, but they also feed on most human foods. House flies become pests when they find access into a home. The house fly can complete its development in as little as six days with each female being able to lay up to 900 eggs. The adults are about 1/4 inch in length. They have four dark strips on their middle section just behind the head. Separating house flies from some other flies that look similar may be difficult. If in doubt, consult an expert. House fly breeding and feeding sites make them potential health hazards.

Blow flies and bottle flies are medium-sized flies with robust bodies.  They usually have a green, blue, bronze or black sheen. The key to identifying blow flies and bottle flies is this metallic shine on their bodies. These flies take about 10 days to complete development.

Blow flies and bottle flies usually breed in decaying animal carcasses. They are important in nature in returning organic matter to the soil. Blow flies and bottle flies appear within minutes after an animal dies. They may also breed in garbage, animal feces, or even meat or fish left out after a meal. Around a home, these flies suggest the presence of a dead animal such as a mouse, squirrel, bird, or stray animal. If eaten, people can get stomach problems, diarrhea, or food-poisoning from these flies. Sometimes blow flies and bottle flies lay their eggs on open wounds of pets and even people.

Since most breeding sites for theses flies are outside, access to the structure should be sealed by keeping screening on windows, doors and vents repaired.

House flies, blow flies and green bottle flies usually do not occur in large numbers inside buildings. If they do, it means that the breeding site is probably indoors or in a place near an open vent, window, or doorway. Check chimneys, attics, crawl spaces, vents, under floor boards, and above ceiling tiles for the source.

Non-chemical control

Removing the breeding sites for these flies is the best method of  control. Breeding sites are often easy to eliminate with a few simple steps. For fruit flies, consider discarding over-ripened fruit or storing it in the refrigerator. Seal recycling containers. If fungus gnats are a problem, letting the soil dry out or repairing leaks will help control them. If you see many house flies, look for fresh animal feces or uncovered garbage cans. Blow flies and bottle flies should have you looking for a dead animal. Good screening on potential entry points will go a long way to prevent these flies from getting inside.

If large numbers of nuisance flies persist after the breeding sources are removed, it usually suggests that a site was overlooked. Keep looking until you find all the breeding areas.

Chemical control

Chemical control should not be necessary after eliminating breeding sites since adult flies do not live very long. However, if the number of flies is excessive, an aerosol spray can be used on the adults after the breeding site has been removed.

Consider hiring a professional pest control operator for large nuisance fly infestations that cannot be controlled with removal of breeding sites.

Originally published 12/98

If this document didn’t answer your questions, please contact HGIC at or 1-888-656-9988.

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