FLY CONTROL - Old Wives Tale or Real?
TRY IT. SOME SAY IT WORKS IF YOU HAVE A FLY PROBLEM. 
We went with some out of town friends to Sweety Pies on Sunday for breakfast, and we sat in the enclosed patio section beside the house. We happened to notice a couple of zip lock baggies pinned to a post and a wall. The bags were half filled with water, each contained 4 pennies, and they were zipped shut. Naturally we were curious! Ms Sweety told us that these baggies kept the flies away! So naturally we were even more curious! We actually watched some flies come in the open window, stand around on the window sill, and then fly out again. And there were no flies in the eating area! 
This morning I checked this out on Goggle. Below are comments on this fly control idea. I'm now a believer! More comments not included here were about pet dogs and fly problems. Zip-lock water bags 
Sue says: Many people swear that a zip-lock bag filled half-way with water and attached over entry-ways will repel flies. No one yet knows how or why it works, but there is speculation that it has something to do with the way the moving water refracts light. If you have tried this please use the comments form at the bottom of the page to share your results with the rest of us. 
ann Says: October 5th, 2008 at 5:51 pm I did tried the ziplock bag and pennies this weekend. I have a horse trailer with full LQ. The flys were very bad this weekend while I was camping. I put the baggie with pennies above the door of the LQ. NOT ONE FLY came in the trailer. The horse trailer part had many. Not sure why it works but it does!!!!!!! 
Danielle Martin Says: September 20th, 2008 at 8:43 pm Fill a ziplock bag with water and 5 or 6 pennies and hang it in the problem area. In my case it was a particular window in my home. It had a slight but significant passage way for insects.Every since I have done that, it has kept flies and wasps away. Some say, that wasps and flies mistake the bag for some sort of other insect nest and are threatened by this. 
maggie Says: June 7th, 2009 at 11:40 am I swear by the plastic bag of water trick I have them on side porch ( our house entry) and all around the basement door. We saw these in Northeast Mo at an Amish grocery store & have used them since. They say it works because a fly sees a reflection & won't come around. 
Just DJ Says: May 16th, 2009 at 7:25 pm Regarding the science behind zip log bags of water? My research found that each of the millions of molecules of water presents its own prism effect and given that flies have a lot of eyes, to them it's like a zillion disco balls reflecting light, colors and movement in a dizzying manner. When you figure that flies are basically prey for many other bugs, animals, birds, etc., they simply won't take the risk of being around that much perceived action. I moved to a rural area ant thought these "hillbillies" were just yanking my city boy chain but I tried it, worked immediately! We went from hundreds of flies to seeing the occasional one, but he don't hang around long.