Porches provide a place to relax and enjoy a cool breeze during the hot summer months—until the flies show up. Flies swarm your porch for the food and breeding places it provides, bringing noise and disease along with them. Eliminate the attractions on your porch and you eliminate the flies.

...
Keep flies off your porch with preventative methods.

Food Items

If anyone has recently eaten on your porch, this may be the cause of your fly problem. Flies eat some of the same things people like to eat, including sugary foods. Spilled tea, lemonade or soda, for example, evaporates, leaving behind a sticky residue that attracts flies. Since residues may be hard to see, rinse your porch with water to dissolve it. Flies also like food scraps such as rotting meat, so search your porch carefully and dispose of any garbage in a bin with a secure lid.

Strong odors attract flies, so even unopened food can cause them to swarm your porch. Overripe fruit, for instance, attracts flies with its alcoholic smell, as do yeast-containing foods like bread. Keep these foods off your porch to discourage flies. Store harvested produce inside your home and use it before it becomes overripe.

Waste

The smell of feces attracts flies because flies commonly lay their eggs in feces as well as in garbage bins, rotting meat and animal carcasses. Avoid letting pets relieve themselves near your porch and dispose of any feces on the lawn in a trash can with a secure lid.

Health Implications

Aside from being a noisy, bothersome addition to your porch gatherings, flies are a health risk. Due to the less-than-sanitary places they frequent, they often spread illness to humans. Illnesses flies spread include tuberculosis, dysentery and typhoid.

Eliminating Flies

To eliminate flies, remove the things that attract them from your porch. Avoid leaving out food, pick up after pets and dispose of animal carcasses immediately. Clean up spills and remove standing water to deprive flies of needed moisture. Put garbage in plastic bags before putting into bins to avoid leaving food residue.

The University of Rhode Island Landscape Horticulture Program suggests honey bait to kill flies. Apply a coating of honey to the inside of a jar. Turn the jar upside down and use two thin supports, such as two 1/2-inch pieces of wood, to hold the opening of the jar slightly off the ground in your porch. Slide a small piece of ripe fruit under the jar to attract flies. After eating the fruit, flies will become stuck in the honey and die as they try to fly off.