Mother was right?

My Mom sent me an email about water filled bags keeping flies away. They are used on patios and by doorways filled with water and 4 pennies....from Florida to Texas.
Sceptic me thought no way....another Internet myth or old wives tale.Checked it out on Snopes and Google....Seems there might be something to this.Still Mothers are wise and always right. We all know this from our experience. For, we have all grown up on the wisdom's and advice of our moms.
So........
We have a door from the garage into the house that flies cluster around getting into my house.
I hate flies!
My bag of water without pennies has been up for 5 days and so far in a most unscientific test I would say it works, only 1 fly has gotten in .............
Mothers are always right!