If you want to eliminate pest populations without engaging in chemical warfare, there are a number of eco-friendly options available that effectively reduce fly infestations without the use of toxic substances.
Parasitoids or fly predators are the most advanced biological weapon at your disposal. These tiny, nonstinging members of the wasp family ravage fly populations by laying their eggs in the fly pupae (maggots). The predator wasp babies consume the maggots before they sprout wings to become flies. The wasps, available by mail order from biological supply houses, are most effective if they're released shortly after the last winter frost and periodically throughout the spring and summer.
Since the parasitoids don't attack adult flies, you will have to rely on other methods of fly control until the predators establish a foothold. Avoid pesticides because they will kill the parasitoids. If you have neighbors with fly problems, they, too, will have to use the predators, or yours will be overwhelmed.
This article originally appeared in the May 1994 issue of EQUUS magazine.