Competition among and between species of flies is another factor that affects the size and composition of a fly population.
The most notable example is the black soldier fly, Hermetia illucens. Its large larvae churn manure and render it physically less suitable for the survival of other species of fly larvae, and for egg-laying by house flies and other muscoid flies. The slow development of soldier fly larvae results in large numbers accumulating in manure.
The black soldier fly may become extremely abundant in poultry manure (especially in high-rise or deep pit houses), and in swine manure pits; in these types of animal housing it may become the major fly species.
Another fly species important in competing with the house fly is the black garbage or dump fly (Ophyra spp.), whose larvae prey on other fly larvae. Ophyra, like soldier flies, sometimes become very abundant in poultry and swine housing.
Other species of flies seldom compete with each other enough to be a major factor in determining the levels of fly abundance in and around animal facilities. Even a small amount of manure or other breeding material can support large numbers of muscoid fly larvae, and there are usually ample amounts available.