When they discover the ball isn't a host animal, they fly abruptly upward and become caught under the trap's canopy. They continue crawling upward and eventually progress through the hole in the plywood base, through the inverted funnel and into the plastic jar where they cannot escape. A trapping program can remove enough female flies from an area to decrease the horsefly biting rate. This method is best suited for the protection of a few animals confined to small pastures. A third method that uses no chemicals is biological fly control.
Predatory wasps eat the pupae of several species of filth breeding flies.
They attack the common housefly, stable fly, blow fly, lesser house fly, garbage fly, horn fly, and many others. The predatory wasp looks like a small gnat, and it only eats flies in the pupae stage, preventing the flies from ever emerging. The wasps do not bite or sting humans or other animals. The fly parasites are spread at a rate of 1,000 per large animal, or 10,000-20,000 per manure heap. Spalding Labs notes that the insect is unable to reproduce in sufficient numbers to adequately control the pest flies, so they recommend monthly shipments throughout the fly season.