Where did all These Flies Come From??

Has anyone else noticed an increase of flies?  I can hardly go in and out the door without letting those pesky things in.  They are on the screens, on the doors and everywhere.  We've had to get out the fly swatter and make it a daily drudge to eliminate the ones who have invaded the house.  Maybe they are attracted to the house because they smell all those wonderful things I have been canning.  Whatever it is they can go away and stay away.