by David Moore
Manager of Technical Services and Board Certified Entomologist
with contributions by Eric Smith, PhD, BCE
Warm weather is here and along with it comes many flying insects, including large filth flies. The most common of the larger flies that bother us are the house fly, blow or bottle flies, flesh flies.
How can I tell which is which?
- House flies (Musca domestica, Muscidae) are about 1/8-1/4″ long at adulthood. They are dull with 4 narrow black longitudinal stripes on its back (thorax). Just for perspective, house flies account for about 91% of all flies in human habitats throughout the world.
- Blow or bottle flies (several species, family Calliphoridae) are about 1/8-5/8″ long at adulthood and they are metallic blue, green, or dull brassy in color.
- Flesh flies (several species, family Sarcophagidae) are about 1/4-7/16″long when they at adulthood. The top of the thorax has 3 black longitudinal stripes, and the tip of the abdomen is usually red or pink.
I know what you are thinking – flies are everywhere, why should I care?
The simple answer is: disease. The flies we are discussing transmit disease through mechanical transmission. They can be parasitic diseases, bacterial diseases, and viruses.
- House flies are general feeders, developing and feeding on feces, carrion, garbage, fermenting vegetation, etc. The house fly is known to harbor over 100 different disease causing organisms.
- Blow/bottle flies develop and feed on human feces, sewage, carcasses of dead animals, and garbage. Blow or bottle flies are of medical concern due to their ability to cause myiasis (infestation of tissues/cavities).
- Flesh flies develop and feed mostly on carrion or feces exposed in sunlight, but can also be found in garbage and decaying plant material. Some flesh fly species can cause myiasis.
- In the urban environment, all of these flies can be found in pet feces (especially from dogs), poorly managed garbage, and dead animals (road kill, dead diseased animals, those trapped in chimneys, etc.)
What should we do to manage this issue?
There are four basic principles of pest management important in controlling house flies: sanitation, exclusion, non-chemical measures, and chemical methods.
Around our homes, the two primary sources of these large flies is garbage and pet feces/poop. Ensure that your trash cans have a tight-fitting lid, and are emptied at least once a week. Keeping the inside of the trash cans clean and using tied off or sealed plastic bags will help control fly populations. Picking up pet feces as quickly as you can will help control fly populations as well. If you are walking your dog, please pick up after them and throw away the droppings as soon as you can. If you let your dog go to potty in your yard, picking up the feces daily will help control fly populations as well. These actions will reduce the attraction to your home by confining attractive material immediately and then removing it from your property weekly; this is to beat the fly life cycle with takes only about 7-10 days in warm weather.
Keep all doors and windows closed when not being used. All doors that open to the outside should be tight-fitting with no light escaping to the outside at night; install door-sweeps along the bottom to close that gap and weather stripping on the other three sides. This also reduces energy loss. If doors or windows are opened for air circulation, then they must be screened and the screens must be in good repair. There should be no openings around water or gas pipes or electrical conduits that feed into the building. Caulk or plug any openings. Ventilation holes can be a way for flies to enter a building. Ventilation is important to maintaining adequate air circulation within the building, but screening must be used to exclude flies.
The use of such devices as ultraviolet light traps, sticky fly traps, fly swatters, baited fly traps, etc. can eliminate many flies from inside a home. A fly swatter is an economical control method for the occasional fly. You have to be careful with ultraviolet light traps, because if you put them in the wrong spots (light shining outside), you can draw other unwanted nuisance pests to your home.
An exterior application of insecticide may offer some relief where sealing the exterior is difficult or impossible. The residual effect of the material a consumer could gain access to will be greatly decreased due to sunlight, and may not kill flies for very long. For long term control, a pest management professional would be the best option for the homeowner. If a large number of flies are inside your home, you can use an aerosol spray labeled for flying insects.
I tried those things and I still have an issue. What now?
- Call a pest management professional who will inspect your house and yard. They will identify and advise you about fly breeding sites, problem sanitation areas, and routes of fly entry. They can also offer mechanical harvesting devices such as insect light traps, and can apply pesticides if, where, and when required.
- It could be that the source of some or most of your fly problem is coming from adjoining properties. In that case, exclusion will be your primary method of control.
- A pest management professional can apply baits that can help reduce the population that is affecting your family by drawing them to another area on your property.
Because flies are a free-flying insect, control measures will only be partially effective if all parts of a program are not implemented. Remember that fly reduction is a cooperative effort and when you partner with a pest management professional, anything that you can do for sanitation or structural control will help accelerate the resolution. Also, flies are a very common and mobile insect that occur almost everywhere, so you should expect to see an occasional fly inside.