Black flies, mosquitoes and other flying pests can invade your patio and garden, making them uncomfortable places to relax or work. Homemade fly bags are a chemical-free fly-repelling method that doesn't depend on awkward-to-use and unattractive flypaper or flytraps. Whether or not these bags of water and pennies actually repel flies and other insects is up for debate, although some users swear by their efficiency.
Fly bags consist of plastic bags filled with water, and often shiny pennies are added to further confound insects. Durable, clear, 1-gallon, plastic, zip-top bags work well, but use the sturdy, freezer-safe variety or double bag the water. You can use different bags, but ensure they are sturdy enough to hold the water's weight without bursting. Fill one-half to two-thirds of each bag with plain tap water. Popular wisdom varies on the amount of pennies to use, with one to four being the common recommendation, but sometimes more are used.
Hang the bags where flies are troublesome and where sunlight can reach them to cause reflections in the water. Tying a piece of sturdy twine around the top of each bag to create a loop provides a hanger. Hang each bag's loop from a ceiling hook sturdy enough to hold the filled bag's weight. An option is to hang the bags from shepherd's hook plant hangers or from nails driven into fence posts or outdoor walls.
Alternative Construction Tips
Not all fly bags are composed of water or water and pennies. Some fly bags include small pieces of aluminum foil in their water instead of pennies. If it's light reflections that drive off flies, then any shiny material that reflects well through the bags' refracting water should suffice.
Reasons for Their Possible Effectiveness
Theories abound about whether or not, and why, fly bags repel flies or other insects. Those people who swear by the use of fly bags insist the light reflections of the water and pennies confuse the compound eyes of the flying pests, causing them to go elsewhere. Other people theorize that the bags scare away flies, either because they resemble wasp nests or because the flies' own large reflections in the water scare them. Insect expert Zack Lemann, who is with the Audubon Insectarium, however, said in a NOLA.com, Times-Picayune article that he and some Audubon Institute workers haven't found the bags to be effective.