Here is a quick primer on flies, courtesy of Penn State University College of Agricultural Sciences, and some tips on how to keep those flies from turning your home into a petri-dish. Warning: if you are easily grossed out, you may want to skip to the tips section of this article.
House flies are a nasty insect. They feed on fecal matter, discharges from open wounds and sores, sputum, and moist decaying organic matter. You can find this bug anywhere filth and decay live, such as dumps, sewers, garbage heaps, dead animal carcasses, dumpsters, trash cans, etc. Because of this attraction to filth and rot, flies spread bacteria. They are strongly suspected to transmit at least sixty-five diseases to humans. Among them are typhoid fever, dysentery, cholera, poliomyelitis, yaws, anthrax, tularemia, leprosy and tuberculosis. Sounds wonderful, doesn't it?
What could possibly be uglier than the above paragraph? Well--the fact that flies FLY. (It is somewhat implied in the name.) But why is this a problem? Because these filthy insects can quickly and easily get onto your food, plates, silverware, skin, and food-prep surfaces. Let's look at what that means in application. Imagine your cat--or the neighbor's cat--has snagged a bird and left it to die on your lawn. When flies pass by, they are drawn to the decay and rot and crawl all over the bird, digesting pieces of it. They then buzz into your home through a vent, gap, or open door and land on a sandwich you just prepared in the kitchen. You wave the fly away and eat the sandwich. Two hours later, your stomach aches and you're in the bathroom--unaware that the fly made you sick.
Do I even need to get into the fact that flies regurgitate their stomach contents onto the food they eat so their stomach acids can dissolve food matter and make it possible for them to suck it in through their straw-like mouth? I think you get the point.
Flies can be managed with some practical safety measures. Make sure all your window and door screens are in good working condition. Inspect weather strips and doors sweeps, making sure they are sealed properly. Use a caulking gun to seal around fixtures, air conditioning units, pipes, electrical boxes, and other objects that pass through your exterior walls. And keep rotting materials properly disposed of. This means grass clippings, rotting fruit, weeds, manure, and other decaying organic material, need to be in sealed bags or covered trash cans. This will reduce your fly population and the spiders that come to eat those flies.
Get connected to a pest management company. They have gigabytes and gigabytes on how to exclude bugs and mammals from invading your yard and home. Your family will be healthier, and your home will be safer.