Pennies deter hornets

[snopes]

Comment: While at a restaurant in Nova Scotia last fall hornets were
merrily making their rounds at the outdoor terrace flitting from table to
table. One patron stated that placimg pennies on the tables deters hornets
from alighting and bothering diners. How can this be true?

[snopes]

Comment: When I went to Calico Ghost Town in California, I saw a bag hanging above
the door filled with water and not pennies, but two cat's eye marbles in
it. When I asked about it, I was told that the bag was supposed to make
flies think there were dragonflies. I have observed a number of times
when dragonflies have captured and eaten flies. Apparently, the large
round, shiny marbles were meant to look like the Dragonflies eyes and the
way that the water would shine from the sun reflecting on it represented
the clear, shiny wings of the dragonfly.

I don't know how reliable they are, but I have seen false predators sold
at stores as a way to repel unwanted pests.

[Ryda Wong, EBfCo.]

We have a ziplock bag with water and pennies above the back door to help repel flies. It's not perfect, but it certainly helps.