House Flies Bugging You Too?

Kurt Jones, Chaffee County Extension Director

County Fair has come and gone, and one of the left-over benefits from County Fair is a surge of house flies which descend upon our office.  One of the contests that we “enjoy” is to see who is better with the fly-swatter in our office.  I typically suck at it, but I blame the bifocals…

Several species of flies commonly enter Colorado homes. Most are merely nuisance pests.  Others are important because they can transmit diseases. House flies, face flies and blow flies develop in manure and garbage and are commonly contaminated with disease-causing bacteria, including those associated with food poisoning.

The most commonly observed stage of a fly is the winged, adult stage. The immature stage is a pale, legless maggot. When full grown, maggots wander from the breeding site in search of a place to pupate. Many flies complete development (egg, larva, pupa, and adult) in a short period, seven to 14 days, and produce many generations during a typical season.

Although flies most often are a nuisance during the warm season, indoor overwintering is common with cluster flies and face flies.

Blow flies are fairly large, metallic green, gray, blue or black flies found throughout the state. These flies tend to be more common than the house fly and sometimes are called the "house flies of the West." The adults spend the winter in homes or other protected sites but do not reproduce during this time.

Blow fly maggots feed on garbage. They occasionally can be found in homes that are near a carcass of a dead squirrel, rodent or bird they have wandered from. Blow flies breed most commonly on decayed carcasses and droppings of dogs or other pets. The adult blow fly is also attracted to gas leaks.

House flies are the best known of the house-infesting flies but are found infrequently in Colorado. House flies generally are gray, with the thorax marked with broad dark stripes. Most often there is some yellow coloring along the sides, which differentiates them from face flies.

House flies usually are found where humans are present. Larvae commonly develop in or near man-made sources of food and can be found in garbage, animal waste, culled fruits and vegetables, and spilled animal feed. The adult flies feed on a wide range of liquid waste but can eat solid foods, such as sugar. To digest solid foods, house flies liquefy food by regurgitating it. Because of this habit, house flies can pose serious health threats by mechanically transmitting disease organisms. During mild winters, house flies may fly and breed continuously, as temperatures permit.

Sanitation practices that remove breeding areas are fundamental to the control of filth-breeding flies, such as house flies and blow flies. Remove or cover garbage and clean spilled animal feed and manure. Face flies, which typically develop in pasture lands, and cluster flies (earthworm parasites) often are difficult to control by breeding area management.

Screening and other exclusion techniques can be an important management tool for several types of indoor fly problems. Caulk or cover all openings into a home to prevent flies from entering.  Do so before flies enter buildings.  Use insecticides only as a supplement to other controls. Serious problems exist with insecticide-resistant flies and many fly populations are now difficult to control with insecticides.

If I can get this fly to hold still, and figure out which lenses to look through, I may have won today’s fly-swatting contest.  I think he’s laughing at me as he buzzes by…