The Indo-European house fly is small, light, and quick to dodge the reaches of the impending doom of the swatter. Although dirty like his brethren, he is quick to understand that after several swipes of the hand he is unwelcome and generally continues on his quest for sugar and shit. If a window or door is opened to him, he requires little coaxing and obligingly takes the opportunity to leave altogether.
The Egyptian house fly, by contrast, is large and heavy in nature and despite much effort encounters difficulty when trying to stay in the air. As if weezing and spluttering he picks up his huge, bulbous mass and, instead of flying, jumps into the unknown to see how far he makes it before gravity takes over. Wherever he lands, he lands, as this location has been ordained unto him. He refuses to move when "shoo-ed" by the human hand, and firmly plants himself on your forehead for the longest amount of time possible. If the human forehead is shaken, he, too, is shaken. If he is squashed from a lack of desire to move, then so be it, as it has been similarly ordained unto him.