We live in a very old house which gets overtaken by disgusting flies at this time of year. Millions of the blighters. My pest control guy says that they leave pheromones which mean they will just come back year after year and there is nothing one can do. Can that really be the case??? Drives me MAD. I have sprays, sometimes let off those bomb things, hang revolting sticky tape things. Is there anything else one can do? It really is just vile and I can't believe there isn't a solution.....