By Helen from United Kingdom
I have seen this in many different forms, the most popular of these being the mason jar of water with aluminum foil floating in it. I have seen the baggies with the pennies. The idea behind this is the difference in light vibration and waves or refraction. Here is some more info. http://animals.howstuffworks.com/animal-facts/water-bags-repel-flies.htm
I have been in a restaurant that had jars of tin foil all over the place on each table. Also these kept flies off of a neighbor's porch one summer. As for really knowing why, we can only guess!
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