Why did God create flies to bug us?

The last few days, we have been experiencing Indian summer here in Cleveland, a rarity for us in November, and my attempts at concentration have been impeded by the inane bumping of flies across the windows.  Where they came from in these few days of balmy weather and warming sunshine I have no idea.  I hate flies in the house, and one thought led to another until I began to wonder why God has plagued us with the bombardment of flies.

They are not pretty. I suppose they are a part of the food chain, but they spread disease to humans if we allow them to land on our food and then eat or drink it.  Diseases like Giardia and Typhoid have been found on them, and I can think of absolutely no useful purpose for them.  So I wondered, and my thoughts turned to the duality of good and evil.

Did God create the evil in our world?  I am no expert, but I have spent a lifetime wondering about such things as why "Bad things happen to good people", etc.  Sometimes this can be explained by the Law of Karma, but I think the fly question can be answered by the need for us to experience duality:  where there's light, there's dark; where there's love, there's hate; where there's beauty, there's ugliness.  If it weren't for this duality of good and evil, we would have no clue which one is which.  It might refer to the balancing act of neutrons, protons and electrons since the world is vibration.   Evil has to balance out good and we need to experience both in order to make a free choice, which God has given us to learn from.

Because we have the beauty of Butterflies and Praying Mantis, I suppose we have to put up also with the ugliness of mosquitoes and flies.  I'm sure that Entomologists find beauty in all their bugs, but I can't see it in flies, so this is how I explain it.

This is my reality, and I'm sticking to it.