Flies Fear Ugly Bags of Mostly Water

The song “Shoo Fly, Don’t Bother Me!” was published in 1869 — almost 140 years ago.   Flies have been pests for, probably, centuries.  But a plastic bag, perhaps a penny or two, and some water may be the solution.  While by no means scientific fact — some researchers believe that we’re simply conflating a correlation with a causal connection — some entomologists (scientists whose study focuses on insects) think that there could be something to the device on the right being a fly repellent.

Flies have big eyes.  Really big, complex eyes, made up of thousands of little lenses.  These lenses, unlike our eyes, are affixed.  So a fly doesn’t see one big picture, which it can explore by scanning around.  Rather, the fly sees thousands of little images, akin to a kaleidoscope of information, from which it pieces together its environment.

To find its position, the fly can use light — sunlight, specifically, but this applies in varying degrees to non-natural light, too.  With one light source — a bulb, the sun, etc. — that’s great.  But when light hits a bag of water, it refracts, or bends.  Per the theory, these bending light rays cause all sorts of chaos for the fly, which gets confused and disoriented, and flees.

This happens to people, too, in a different way; we call them mirages.  If you’ve ever driven on a hot road, you’ve probably experience this one.   So while the bag of water-as-fly repellent theory is by no means fact, it is certainly plausible.


Bonus factAccording to Wikipedia, the original lyrics of “Shoo Fly, Don’t Bother Me!” were, by modern standard, incredibly offensive.  We’ll not share them here, but you are welcome to click through to see for yourself.

From the Archives: A Fly on the Urinal: How flies (well, stickers of flies) can help with toilet training.

Related: An old fashioned way to rid yourself of flies.