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Natural Fly Repellent

Updated on October 31, 2012

What Do We Mean by "Natural" Anyway?

Many of the active ingredients in natural fly repellents and insecticides are natural in the sense that they exist in nature. Most are extracted from plants, but they don’t exist in nature in the same concentration in which they are used in a repellent. After having been extracted and concentrated, can they still be thought of as natural? In this article, I use the term natural to mean not manmade, but there is often no clear line between what is and isn’t natural.

Natural Does Not Mean Non-Toxic

When people use the term natural, they are generally using it in contrast to the term synthetic. When it comes to insect repellents, there is a tacit assumption that something that is natural is less toxic in a general sense than something synthetic.

We need to keep in mind that just because something is natural, doesn’t mean that it is non-toxic. After all, cobra venom is natural, but extremely toxic. Just because a substance comes from natural sources doesn’t mean that we can be cavalier about how we handle it.


Pyrethrin refers to either of a pair of chemicals obtained from a species of Chrysanthemum. Pyrethrin acts not only as a fly repellent, but as an insecticide and is a common active ingredient in fly sprays. Its effectiveness is well documented. While pyrethrin itself is a natural ingredient, it is often paired with piperonyl butoxide, which is not. Pyrethrin breaks down quickly in sunlight and insects, while initially knocked down, can detoxify it and recover. The piperonyl butoxide prevents the insects from detoxifying the pyrethrin, killing them.

There are some pyrethrin sprays out there that do not contain piperonyl butoxide and there are some that are OMRI approved. OMRI is the Organic Materials Review Institute and is the organization that approves materials for the use in organic agriculture in the United States


Don’t be confused by ingredients with names similar to pyrethrin, like permethrin. There is an entire class of synthetic chemicals call pyrethroids that are used for insect control. These chemicals are designed to be more toxic to insects and less toxic to mammals than pyrethrin, but they are synthetic, so if natural is what you are after, stick with pyrethrin. Pyrethrin itself is of low chronic toxicity to humans.

Essential Oils

Essential oils are a broad class of volatile organic oils extracted from plants. Many have well known insect repellent and insecticidal properties and there are a variety of fly repellent sprays available that contain these oils. Do they work? My research indicates that the answer is sort of. The efficacy of these products doesn’t seem to last as long as those containing synthetic chemicals and they need to be applied more frequently.

Many people want to use essential oil fly repellent sprays on their horses and livestock. This isn’t likely to cause any harm, although I would pay close attention to any skin sensitivity that the essential oils might cause. My concern is that the animal isn’t going to be protected for very long. Essential oils are said to be volatile because they evaporate easily. Most of these products need to be applied every couple of hours.

Are Essential Oils Safe?

The United States Food and Drug Administration classifies many essential oils as Generally Recognized as Safe (GRAS) and they can be used as food additives. However, they still need to be handled with care. There are lots of DIY recipes for essential oil fly repellents on the internet. Be careful handling these very concentrated oils. I have blistered both my wrists quite badly with thymol, an extract of thyme.

Bag of Water and Penny Poll

Have you ever used a clear plastic bag filled with water and a penny to repel flies?

See results

The Old Bag of Water With a Penny Trick

Some of you might have heard that a clear plastic bag of water with a penny in it will repel flies. I have seen this tried in a horse barn and I can’t say that I saw any positive effect whatsoever. It’s not going to hurt anything though, except maybe waste a plastic bag.

Other Home Remedies

There is a bewildering array of potions, concoctions, and brews that are said to repel flies. Besides essential oils; vinegar, mouthwash, and garlic are frequent ingredients. While these substances might have some repellent effect there is no scientific proof, just anecdotal evidence. Give them a try; they might not work, but they are not likely to hurt anything.


Flower and vegetable oils. (1993, December). Retrieved from

Goodyer, L. I., Croft, A. M., Frances, S. P., Hill, N., Moore, S. J., Onyango, S. P., & Debboun, M. (2010). Expert review of the evidence base for arthropod bite avoidance.Journal of Travel Medicine,17, 182-192. Retrieved from Review of the Evidence Base for Arthropod Bite Avoidance.pdf

Gouge, D. H., & Olson, C. (2011, August).Choosing a bug repellent. Retrieved from

Gray, L. (2009, April 6).Natural fly repellent. Retrieved from

Ibrahim M. A. et al. (2001). Insecticidal, repellent, antimicrobial activity, and phytotoxicity of essential oils: With special reference to limonene and its suitability to control insect pests.Agriculture and Food Science in Finland,10, 243-259. Retrieved from

Isman, M. B. (2000). Plant essential oils for pest and disease management.Crop Protection,19, 603-608. Retrieved from

Johnson, A. (2009, August 27).Catnip shows promise as fly repellent for cattle. Retrieved from

Moon, R., & Gilkerson Wieland, B. (2008).Fly control around horses. Retrieved from

Citronella (oil of citronella) (021901) fact sheet. (1999, November). Retrieved from

Piperonyl butoxide. (n.d.). Retrieved from

Pyrethrins. (1994, March). Retrieved from

Pyrethrins & pyrethroids. (n.d.). Retrieved from

Townsend, L. (2007, May).Insect control for horses, horse barns and stables. Retrieved from


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    • Teresa Coppens profile image

      Teresa Coppens 5 years ago from Ontario, Canada

      Interesting article Wib. They are a nuisance around early spring and later in the summer here. I find that wasp traps (filled with sweet juice)kills off just as many flies and keeps the population down near the house. Walking in our forest in spring and fall, that's a whole different problem. Deer still seems to be the most reliable but even that's not foolproof. Great overview Wib.

    • nifwlseirff profile image

      Kymberly Fergusson 5 years ago from Villingen Schwenningen, Germany

      I've never tried the copper coin trick, Australia got rid of it's 1 and 2 cent coins a long time ago.

      I have used citronella essential oil on the underside of a baseball cap while hiking (on the brim, not where it touches skin). It does seem to help, but stinks terribly!