If one fly buzzing around your house is annoying, then an entire infestation is an absolute nightmare. It's normal to have a fly in the house every now and then, and there's even a type of fly you'll want to keep in your garden for an unexpected reason. However, you will be able to recognize a problematic infestation by the sudden, dramatic increase in fly sightings. You may hear flies buzzing even if you can't see them. Once you've surveyed the severity of the infestation, you can take steps to eliminate it.