A Strange, Easy Way to Discourage Flies

By , May 16, 2013

Flies are one of the plagues of summer. Controlling them seems impossible; deterring them is difficult. Yet, we’ve learned an improbable but effective method of discouraging flies.

Generally, I hold that if you learn something from a forwarded email, you haven’t learned anything at all. Every once in awhile, though, a commonly-forwarded email can provide useful information! This is one such case.

The email suggests hanging a plastic bag full of water wherever you wish to discourage flies. It will ground or chase them all away! No one seems to know why this works; one guess is that the diffracted light overwhelms a fly’s compound eye, signaling far too many predators to deal with . . . or something like that.

We usually don’t have a big problem with flies, but the summer we tried this, we had been away from the homestead for a month. The keepers used the guest outhouse pit toilet exclusively, so the composting outhouse remained undisturbed long enough for flies to accumulate. When we returned, we hung a plastic bag of water in the window. The flies were gone the next day. Actually, they weren’t gone—they were grounded. We found them hiding under the “seat of ease” platform, from which they refused to budge, making them easy prey for a fly swatter. Within a day, the email suggestion solved our fly problem!

The message also suggests putting a penny or two in the bags. This may discourage algae growth, perhaps? We didn’t do that, and still had success. In fact, we’ve left the same bag of water hanging in the outhouse window since we learned this trick; to this day it’s clear, and still keeps the flies under control. Maybe this is because we live in a cooler climate? In hotter regions, the pennies might be necessary.

If you have a problem with flies this summer, try this method. If it works for you, tell your friends you learned it from our blog—a far more prestigious source than a forwarded email!

Note: A popular bit of trivia holds that Alaska has no houseflies. I don’t know if that’s true or not. We may technically be free of that particular type of fly, but we have plenty of flies that are very close to them in appearance and behavior.

4 Responses to “A Strange, Easy Way to Discourage Flies”

  1. Astrid says:

    We have tried this a few years ago..I am happy it works for you..it doesn’t for us.

  2. Mark Zeiger says:

    Maybe you have a better class of fly? 🙂

  3. Ekij says:

    Does the plastic bag need to be a clear (transparent) bag or will a standard bin-liner white (translucent) bag work? I assume an opaque bag such as a black bin bag will not work (how could the files know it has water in it?)

  4. Mark Zeiger says:

    Ekij, the piece I read on it specified a clear/transparent bag. The theory seems to be that light refracted through the bag may be what “scares” the flies.

    By the way, the original bag we used still hangs in our outhouse, discouraging flies. We never added pennies to it, and never got any algae in it. Guess we’ve been lucky!

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