Flies do not typically live in groups. They are often nomadic, following food sources. They often choose to make habitats in areas prone to trash and dirt. They feed on decaying matter, trash and fecal matter.
Sanitation is the number one cure for eliminating flies. You can eliminate the threat of these flies by keeping your home free of garbage. If you have a dog or cat, pick up feces as soon as possible to reduce the possibility of an infestation. Your garbage can should have a lid to prevent flies from finding a feeding ground.