"Ummm, what's this for?," I asked my friend Paulina, holding up a plastic bag, partially full of water and about a half-dozen pennies, that was on her kitchen counter. Thinking back to my childhood, I figured it was some crazy science experiment her children were in the middle of.
"It keeps the flies away," Paulina said.
I looked around her kitchen - no insect activity. Paulina said that her kitchen had been swarming earlier and, after using this trick for a few weeks now, is sold on its effectiveness.
Making up the magic fly deterrent is easy: drop about six pennies into a zippered plastic bag. Fill it halfway with water. Close up the bag. Paulina keeps hers on the counter, but other people have hung them up in doorways or from window frames (tie a rubber band around the bag just under the zipper and pull out one loop to use for hanging).
There are theories about why it works. The prevailing one is that the water's ability to refract light may be be visually confusing to flies, though I'm just as inclined — my childhood scientist rearing her head again — to think it has something to do with a reaction between the metal in the pennies, the water and the plastic. Many detractors dismiss it as a hoax. But, given that the cost of making one is, literally, a few pennies, I'd say, if flies are the bane of enjoying your summer, it's worth a try.