Anywhere manure accumulates and stays reasonably dry there will be an abundance of mites and beetles that prey on fly eggs, maggots, pupae and even adult flies that use them for their own reproduction.
Dry manure means a more active and effective population of natural predators and parasites.
Cultural methods undertaken to manage manure and biological methods implemented to kill flies are therefore complimentary. Letting nature take its course would be acceptable under most natural conditions. However, high animal density in poultry, dairy, feedlot and farming operations produce large amounts of animal waste in short periods on relatively small areas. Fly populations can be correspondingly great. Therefore, it is necessary to supplement natural populations of predators and parasites with commercially produced fly parasites to increase the number of flies that are killed.