Relaxing on your  porch during long summer nights is a great way to unwind after a long day. But if you even think about bringing a snack, it seems flies from the surrounding area get a special memo and show up to ruin your perfect evening. If you're tired of swatting flies instead of relaxing, try this tactic from Instructables for keeping the bugs at bay. 
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You'll need:
-Clear plastic storage bags (quart size is fine)
-2 1/2 cups of water
-2 teaspoons of water
-Lime juice
-Pennies (an alternative version uses tin foil)

In a bowl, combine your water, salt and lime juice. Mix well. Pour the water into your plastic bag and toss in your pennies or tin foil. Seal the bag completely. You'll need to hang these bags outside the area you plan to sit. You can stick a paperclip through the top of the bag (above the seal) to create a hook to hang it, or puncture a hole and tie a string. 

Mr. Aviator explained to Instructables readers why this works, "Flies have visual receptors called ommatidia. Unlike humans, they don't have pupils that control the amount of light that enters their eyes ... Therefore the reflective light ... scares them because they can't focus ..."

Myth Busters ran an experiment to see if this method actually works.  While they determined that it wasn't effective, their experiment only included bags of water (without pennies or tin foil) and they used a fair bit of raw meat to attract the flies. 

In any case, it never hurts to try. Have you ever used this method to keep flies at bay? Tell us about your experience in the comments below.