Getting rid of flies that infest indoor spaces is one thing, but it can be next to impossible to keep them out of your home if there are hoards of flies outside. Flies can make any form of outdoor recreation or activity unpleasant, and heavy fly infestations outdoors can be an ongoing problem in certain climates, or in environments where there are many animals, such as on farms or in homes with dog kennels, chicken coops, or located near meadows and pastures.
There are two approaches to combating flies outdoors. First, you can try to eliminate and repel them from the immediate area where you are trying to enjoy outdoor activity. This can be a rather temporary solution, but it can at least allow you to claim some outdoor space to enjoy a picnic or game of badminton on a nice evening. Second, you should also combat flies at the source—by denying them the feeding and breeding areas that lead to heavy infestations. This can make your yard more enjoyable through the summer, and also reduce the number of flies that sneak into your home.
Understanding the Lifecycle of Flies
At some times of the year, it's be nearly impossible to eradicate flies from outdoor environments. From spring to fall in North America, the common housefly (Musca domestica,) is actively breeding, reaching a peak of activity during mid-summer. The species requires only moisture and some decaying organic matter in order to breed and thrive. During the warmth of summer, even just a pile of dead leaves moistened by rainfall can quickly become a breeding ground for flies. Unless you live in the middle of an enormous asphalt parking lot, it will be nearly impossible to avoid flies entirely during the summer months.
A mature female housefly can lay up to 500 eggs in its short lifespan. The eggs hatch into larvae (maggots) within a day, and in as little as a week those maggots will proceed through the pupal state and hatch into flies. A day later they will be breeding adults. Eradicating flies entirely is not a battle you can win in the warmth of summer. The best you can hope for is to repel flies from the areas where you want to enjoy outdoor recreation and to reduce the overall number of outdoor flies by controlling the feeding and breeding opportunities.
What Is a Fly?
By the scientific definition, a "fly" is any insect in the Diptera order of insects, identified by the presence of only a single pair of operational wings, rather than the two pairs found in many other insects. By definition, mosquitoes are a type of fly, but when we think of the pesky fly that can make summer living unpleasant, it is the ordinary housefly (Musca domestica), the 3/8-in-long buzzing insect with the bulging eyes, that we usually picture. Less commonly, we may be combatting the much larger horse-fly (Tabanus spp.) or the black fly (various genera), both of which can inflict painful bites.
7 Ways to Get Rid of Flies Outdoors
There are many dozens of species of flies, but eradication methods are largely the same for all of them.
Identify and Eliminate Food Sources and Breeding Areas
Any decaying organic material, including plant- or animal-based matter, combined with a small amount of moisture, will naturally become a haven for flies to feed and lay eggs, which will quickly hatch into maggots that will very shortly mature into more flies. Long-term control of flies, therefore, requires that you identify and eliminate these sources of food and moisture.
If you have ever visited a farm, or live on or near one, you will recognize that pastures or barns with animal droppings are havens for flies. But similar issues can exist even around an urban home if pet droppings, compost piles, or even piles of dead leaves or brush are allowed to decay.
Fly activity will be most apparent on warm summer days. Look for small swarms of flies, which will identify the sites where the flies are feeding and laying eggs. The house fly can complete its life cycle in as little as a week, so any wet organic materials and manure need to be removed, and garbage picked up at least twice a week to break the breeding cycle.
Clean up or otherwise alter any sites where the flies are seen to be living and breeding, and any that are attracting them to feed:
- Use tight-fitting lids, and clean trash bins regularly. If you use plastic bags, ensure they are well sealed.
- Pick up pet feces regularly, and remove any dead or decaying plants.
- Keep dog kennels clean, pick up food after the dog's feeding time as much as possible, and clean up any spilled food or water.
- Eliminate areas of pooling, stagnant water, and other excessive moisture around the yard.
- Keep compost piles far from the home and properly managed to keep flies to a minimum.
In almost all cases, flies found inside the home have entered from the outside. Therefore, barriers preventing access to the building are the first line of defense:
- Seal cracks around windows and doors where flies may enter.
- Use well-fitted, small-mesh, well-maintained screens on all doors and windows
It's not just the main house where you should practice these measures. Sheds, garages, gazebos, and porches should also be protected from infiltration by flies.
Encourage Natural Predators
Many birds and virtually all bats will feed heavily on many insects, including houseflies. Flycatchers are a variety of thrush, and they earn their name for good reason: they are prodigious hunters of flying insects. Other members of the thrush family are equally good at eating flies, as are purple martins. And many other birds feast on maggots and larvae, offering preemptive control of flies. Bats are typically night hunters, and they can eat huge quantities of flies in the early dusk hours.
Do what you can to encourage insect-eating birds and bats in your garden. A few bird and bat houses, along with a birdbath, can greatly reduce your fly population.
Frogs and other small amphibians in your garden will also consume both adult flies and their larvae.
Trap the Flies
Trapping can have limited impact in the open air, but they can provide some reprieve if set away from areas where people will be. Traps set some distance from a picnic area can make your meal much more pleasant. The key is to not attract flies toward or through the area, but rather to intercept flies before they get to you. Consider these trap options:
- Inverted cone traps containing fly food attractants are widely available and can be effective if sanitation is maintained in the area. The fly food attractants can be very foul-smelling, so the traps should be placed away from occupied structures.
- Insecticide-impregnated resin strips, ("fly paper") can be placed on the inside of garbage can lids to attract and eliminate flies that get into the trash. If your dumpsters seal tightly, fly paper strips can be used there as well.
- Although they may have little effect in outdoor areas, ultraviolet light traps can be placed in alleyways, beneath trees, and around animal sleeping areas and manure piles to attract and kill flies.
On a deck or patio, a surprisingly effective method is to set up an oscillating fan near your grill or picnic table. Flies don't maneuver well in strong breezes, so this can be a very good strategy. If your deck or patio has an overhead structure, a permanent overhead fan is also an option.
Special citronella candles, comprised of aromatic oils distilled from lemon grass, will repel both flies and mosquitoes. You may need to light several candles to effectively repel flies.
Make DIY Fly Strips
You can make your own fly-repellant strips by soaking strips of cloth with scented oils, such as clove, lavender, lemongrass, citronella, eucalyptus, rosemary, or mint. Tied onto tree branches or railings, the scent is remarkably effective at repelling flies.
What Causes Flies Outdoors?
Flies appear in outdoor locations wherever and whenever there are food sources (decaying plant and animal material) and moisture. Darkness also enhances the breeding, hatching, and development of larvae into more flies.
How to Prevent Flies Outdoors
Preventing flies is mostly a matter of denying them the food and moisture necessary for reproduction. This, combined with various methods of trapping, natural predation, and repellant methods, can keep fly populations under control.
Do Flies Carry Disease?
Flies are rightly considered rather filthy insects because they actively feed on feces and other decaying matter. As a result, they can spread a wide variety of germs, including the various bacteria that cause anthrax, typhoid, stomach ulcers, cholera, dysentery, and tuberculosis. This is worth remembering the next time you see a fly land on the hamburger that's just come off the grill.
Should I Use Traditional Spray Pesticide?
Chemical control should not be used unless all other methods have failed because flies have become resistant to many insecticides. This has steadily made fly populations more difficult to control with such chemicals. The winds and air patterns also make these sprays difficult to control in outdoor locations.
That said, a proper fogger insecticide can be an effective temporary measure to repel flies and stinging insets if applied an hour or so before a picnic or outdoor gathering.
When using any pesticide, be sure to read the product label and follow all directions. Make sure to store the product safely, away from where children or pets can reach them. Chemical pesticides are best regarded as a last resort measure, used with great care. Remember that most of these products will also kill beneficial insects, such as pollinator bees.
Make sure that no insecticide contacts food or areas where food will be prepared or consumed.
What About Residual Insecticides?
Properly labeled residual pesticides can be used in areas where flies are seen to rest, such as the outside surfaces of homes and overhangs. A pest management professional is the best person to apply these residual insecticides, since they may be subject to restricted use or be otherwise unavailable to homeowners.
If insecticides are used, they may have to be reapplied every two to four weeks during warm weather.