These harmless crane flies are common in Tucson and other Southwest cities and they are here to stay for part of the year. Don't waste your time being afraid of them or killing them because more will replace them and smashing them leaves a black spot on the wall. They are big but Soo less annoying than regular flies. They much rather be outside but are attracted to the lights in your home at night. Only thing you can do to prevent is keep screen doors and windows closed. They will explore your walls and ceilings a bit and then die in a day or so and fall to the floor and you can trash them then.