You Asked:

Does filling a plastic bag with water and dropping a penny in the bottom keep flies away? — Melinda, Joshua, Texas

Marshall Brain answers:

You can find lots of Web pages describing this idea. Basically you take a one-gallon Ziploc bag, fill it with water and either hang it or set it on the table. It is supposed to keep flies and wasps away. There are many theories put forward on why this would work, E.g. – the bags resemble spider webs, the bags reflect light in random patterns, the bags act like lenses, etc.

However, Joe Graeden of People’s Pharmacy put bags of water to the test. He placed two bags near a hummingbird feeder that has a problem with wasps:

Will Water Ward Off Wasps?

After performing the experiment he says: “My “scientific” report is that the bags did NOT deter the insects AT ALL. The bags were in shade when I started the experiment, and now they’re in full glaring sun. So “light” doesn’t seem to have anything to do with the bag theory.”

Looks like this is another Urban Legend.