There are two main flies seen around all summer:
House Fly (AKA filth fly, garbage fly)
Blow Fly (AKA bottle fly, blue fly, green fly)
Both types can spread disease easily because of the way they digest their food and eliminate their waste. When feeding, these pests regurgitate liquid from the stomach to dissolve food, and then use their sponging mouthparts to suck it up. They leave fecal spots, or “specks,” where they have walked. Because of these habits, they are capable of transmitting filth-related diseases such as diarrhea and dysentery.
How long can infestations last?
Flies are attracted to decaying organic matter and some of them need this matter in order to breed successfully. If you are trying to figure out where they come from and how to get rid of flies, the first two steps you need to take are to identify the type of fly infestation you have and then locate the source of the decaying matter that is allowing them to thrive.
Some types of flies are capable of living and breeding entirely indoors while others can only spend part of their life-cycle inside. Experts at the Texas A&M AgriLife Extension point out that the flies that can complete their entire life-cycle indoors are typically less than 1/8 of an inch and include the phorid fly, fruit fly, drain fly, and the fungus gnat. The fact that these types of flies can go through the entire life-cycle inside means that an infestation can go on indefinitely as long as these pests have access to a food source.
Larger breeds can be more than 1/4 of an inch in adulthood. These larger flies include the house fly, soldier fly, flesh fly, and blow fly. These types do not typically breed inside because they need decaying matter such as animal feces, garbage, or animal carcasses for breeding. If you are having trouble with large flies inside your home it could be an indication that there is a breeding site nearby. For example, if a rodent dies in your attic or inside of a wall, it can provide these pests with the breeding environment they need. The infestation will continue until you take steps to eliminate the breeding ground of the flies.