Shoo Fly, Don’t Bother Me…..

By Marcia Anderson

Summer is a glorious time for an outdoor family BBQ.  Those interested in nature can watch all of the animal families busily foraging for food. Rest assured it won’t be long until you hear the familiar buzz of house flies.

Adult house fly. Image: David Cappaert

Adult house fly.
Image: David Cappaert

The good news is that house flies cannot bite, unlike mosquitoes, because their mouth is no more than a spongy pad. The bad news is that one landed right on my macaroni salad. Like most people, I shooed the fly away and went back to eating. However, I pushed the food that the fly touched to the side of my plate and did not eat it. I also washed my hands when I went inside for there is no way to know where that fly had been, and where else it had landed.

Why am I so paranoid over a fly you ask? Because a house fly potentially carries twice as many pathogens as a cockroach, and they transmit infectious bacteria at levels high enough to be a significant public health risk. As a matter of fact, many common infectious diseases, ranging from food poisoning to respiratory infections, are transmitted by house flies. Some of the most common diseases spread by the house fly are typhoid fever, tuberculosis, dysentery, food poisoning, and diphtheria, all of which can be serious if not treated promptly.

The University of Florida recently found even more pathogens transmitted by house flies. The bodies of healthy people can usually isolate and fight off numerous pathogens before they become a problem. However, these same pathogens are a serious health risk to many people with developing or compromised immune systems, including infants, young children, senior citizens and those recuperating from illness. For me, ingesting a potentially harmful pathogen is just not worth the risk.

Since they do not bite, exactly how do house flies transmit diseases? House flies pick up pathogens from a wide range of feeding places such as organic matter, feces, fruits, vegetables, meat, and open wounds, just to name a few. At first, the fly regurgitates saliva and digestive juices onto their food then sponges up the solution. Their saliva actually liquefies their food. This way of feeding allows flies to contaminate large amounts of food.

Head of an adult house fly. Image: Pest and Disease Library; Bugwood.org

Head of an adult house fly.
Image: Pest and Disease Library; Bugwood.org

A house fly needs only a few seconds to contact a pathogen source in order to transport it elsewhere.  Sometimes, only a few microbes attached to the flies’ body, legs, or mouthparts can cause a serious disease. For all of these reasons, fly control needs to be taken seriously. You do not need a lot of flies to contaminate food sources, hence the need to heed health department requirements in school kitchens and restaurants. Limiting fly contact with food, utensils, food preparation areas, and people is an important part of hygiene.

Integrated Pest Management (IPM) is the smart, sensible approach to controlling flies and other pests.  IPM is not a single pest control method but rather involves multiple control tactics based on the biology of the pest and site information. Consequently, every IPM program is customized to the pest prevention goals of the situation. Successful IPM programs use a tiered tactics that include: proper pest identification and monitoring; pest prevention through cultural controls such as sanitation; maintenance that eliminates entry points and food/water sources; pest control devices; and pesticides, as needed.

First, focus on pest prevention through exclusion. If flies cannot get into an eating area, they will not be a problem. Providing barriers, such as screens on doors and windows, nets, self-closing doors, and sealing cracks that provide entry points create a good first line of defense. Even air curtains (fans blowing air down over a doorway) will keep them out.

Next take up sanitation. Garbage should be placed in plastic bags and held in containers with tight-fitting lids. It should not be allowed to accumulate. Reducing the sources that attract flies, such as pet excrement, soiled baby or adult diapers that have not been discarded properly is key to IPM and fly prevention. Open piles of compost, animal manure, garbage, lawn clippings, decaying vegetables, fruits, and dead animals are also breeding sites and pathogen sources for flies.

For flies, the larval stage is the easiest to control. If breeding sites can be eliminated, the lifecycle of the fly can be broken, thus preventing more adult flies.

After sanitation and maintenance, there are devices that can assist in fly control. They include ultraviolet light, air curtains on doors, inverted cone traps that contain attractants, and the old fashioned fly swatter.

Penn State University offers an informative fact sheet on house fly control to help you get started. Once you’ve taken on the fly management challenge, you can enjoy your next meal without the buzz of these troublesome pests.

About the Author: Marcia is with EPA’s Center of Expertise for School IPM in Dallas, Texas. She holds a PhD in Environmental Management from Montclair State University along with degrees in Biology, Environmental Design, Landscape Architecture, and Instruction and Curriculum. Marcia was formerly with the EPA Region 2 Pesticides Program and has been a professor of Earth and Environmental Studies, Geology, and Oceanography at several universities.

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