My friend told me that if you put a penny in a plastic sandwich bag with a little bit of water that it will keep the flies away.We tried it recently and it seemed to help.How does this work????

The flies are scared of anybody who would believe in such nonsense, so they stay away!

The reflections from the water scare the common housefly, as it has vision which far exceeds that of other insects.

It should work without the penny, but it adds some more visual stimuli to keep them away.

The myth is that hanging the bag in a doorway will keep flies away, not just out in the open. Time to send this one to Mythbusters.