1. Fly Killer Instructions The Fly Killer Parasites will be shipped to you in a bag with wood shavings Depending on temperatures they will begin to hatch within 2 5 days after arrival When you start to see them moving around inside the bag it is time to release For best results scratch about 1 2 inch hole in several areas Choose fly breeding spots such as manure piles and garbage collection areas Place some of the Fly Killer Parasites in the hole and lightly cover with dirt or manure They will move around in a 100 yard radius in seatch of fly pupae Use of fly baits or traps can help with the existing adult fly population Be careful with spray chemicals as they will kill these fly predators as well Flies can also develop chemical resistance to sprays