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, and especially bothersome are flies. In this blog, we’ll discuss only the larger flies which are also called filth flies; we’ll do the small flies in the other blogs.
The most common of the larger/filth flies that invade homes are the housefly (Musca domestica, family Muscidae), blow or bottle flies (several species, family Calliphoridae), flesh flies (several species, family Sarcophagidae).
How can each group be identified?
House fly: Adults are about 1/8-1/4″ long. Their color is dull gray, the top of the thorax (part to which the legs and wings are attached) has 4 narrow black longitudinal stripes, and the abdomen usually has its sides pale.
Blow or bottle flies: Adults are about 1/8-5/8″long. Their color is usually partly or wholly metallic blue, green, or dull brassy.
Flesh flies:. Adults are about 1/4-7/16″long, very robust in form. Their color is dull blackish gray, the top of the thorax (part to which the legs and wings are attached) has 3 black longitudinal stripes, and the tip of the abdomen is usually red or pink.
Why is their control desirable other that the fact that they are a nuisance?
The house fly is known to harbor over 100 different disease causing organisms. Blow or bottle flies are of medical concern because of their mechanical transmission of disease organisms and ability to cause myiasis (infestation of tissues/cavities), and flesh flies because they develop in fecal material or garbage and some species can cause myiasis.
Where do these flies breed?
House flies are general feeders, developing and feeding on feces, carrion, garbage, fermenting vegetation, etc. Blow/bottle flies develop and feed on human feces, sewage, carcasses of dead animals, and garbage. Flesh flies develop and feed mostly on carrion or feces exposed in sunlight, but can also be found in garbage and decaying plant material. 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.)
How fast can they develop?
In the summer, most of these flies can go from egg to adult in about 7-40 days. The house fly female averages about 350-900 eggs which require only about 6-10 days, with adults living 15-25 days. Blow/bottle fly females lay up to 2,000+ eggs which require 10-99 days depending on the species. Flesh flies give birth to living larvae and their life cycle (adult to adult) varies from 8-36 days depending on the species.
How are filth flies managed?
This consists of sanitation to limit attraction, exclusion to limit access into the home, and harvesting/killing those that do manage to get inside. Just killing the adult flies will rarely if ever solve the fly problem, because the breeding source(s) must be located and eliminated, and/or their entry prevented.
- Attraction. Reduce the attraction (see “where do these flies breed” above) to your home by confining attractive material immediately (plastic bags and/or trashcans) and then removing it from your property weekly; this is to beat the fly life cycle (egg to egg) with takes only about 7-10 days in warm weather.
- Sources. Around homes, the two primary sources of these large flies is garbage and pet feces/poop, with dead animals a distant third (outside or inside, especially in chimneys).
- All garbage should be contained in trash cans that have a tight-fitting cover, that are lined with a plastic bag, and that are emptied at least once each week.
- Inside trash cans should have a tight-fitting lid and be emptied at least once each week; tie off or seal the plastic bag before putting it in the outside trashcan.
- Keep the inside surfaces of all trash cans clean.
- If you take your pet out on a leash, pick feces up as soon as they are deposited using the inverted bag technique (turn the bag inside out and use it like a glove, pick up the poop, pull the bag bottom with poop back to its original position, and tie off the bag or close the seal if it is a Ziploc-type). Put this bag in the trashcan.
- If the pet runs in your yard, remove the feces daily. Use the inverted bag technique, or a pooper scooper to transfer the poop into the plastic bag, tie it off, and put the bag in your trashcan. Be sure to hose off the scooper (preferably into a drain) to keep it clean.
- Keep all doors and windows closed when not being used; install self-closures on screen doors.
- All doors that open to the outside should be tight-fitting; that is, no light should escape 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.
- Fireplaces should have an exterior screened cap to keep animals out; animals often get trapped and die in chimneys.
- For the occasional fly, use a fly swatter.
- For a few flies, fly ribbons or sticks (paper with a sticky surface) work but are usually considered unsightly. These work best if hung in dead-air spaces and/or under ceiling lights, and if hung about 4-5 feet above the floor. If hung higher, they will harvest flies primarily at night when they look for a place to roost.
- Individual rooms can be treated by applying or releasing an aerosol pesticide formulation according to label directions. Do not over apply.
If you don’t want to or can’t solve your fly problem
- 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.
- Remember that fly reduction is a cooperative effort and that you must do your part. Also, flies are a very common and mobile insect that occur almost everywhere, so you should expect to see an occasional fly inside.