Does Peppermint Oil Work to Get Rid of Ants?
We’ve learned our lesson using powerful chemicals to control pests, such as the invention, and subsequent banning of D.D.T (Dichlorodiphenyltrichloroethane) in the 1940s. DDT was heralded as an extremely effective insecticide, intended to eradicate pests that carried malaria and dengue fever, yet its effects on nature were destructive and widespread.
The widespread usage of D.D.T ended up killing important ecosystems such as birds and fish, not to mention mosquitos developed a natural tolerance to the stuff.
For that reason and others, the world now looks fondly on more natural insect repellants. Countless blogs proclaim the virtues of all-natural, homemade house pest remedies, such as garlic sprays, mint leaves, and sprinkling cayenne pepper around ant nests.
Many of these natural remedies have been shown to be quite ineffective in scientific studies, except for a very small few. Two natural insect repellants often stand out above others, for their efficacy and safety in use. The first is diatomaceous earth, and the other is peppermint oil.
Organic Lesson says that household pests such as ants are repelled by the scent of peppermint while mentioning other useful ways to control house pests with non-chemical methods.
Many of the organic pest control blogs out there offer many solutions, but rarely explain how or why these solutions work. Then we get myths like coffee grounds being effective at controlling pests, based on anecdotal evidence, while other blogs debunk these myths.
In this article, we’re going to summarize a collection of actual scientific studies focused on peppermint oil as an insect repellant.
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Do Ants Hate Peppermint
If you were to walk around a peppermint plant, you might be surprised to see that ants are using the plant as their home. In fact, they don’t seem to mind if you accidentally step on it and make a mess of their home.
Ants hate peppermint because it smells like a predator’s scent – mint is one of the strongest predators in nature and the smell will make them move out of its way.
A field study done in Germany found that ants responded to the smell of peppermint by moving up away from the plant. The peppers were positioned at different heights on different plants but all had a mint scent on them. The peppermint plants with no mint scent had no ant movement around them.
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What is Peppermint?
Peppermint (Mentha piperita) is a perennial herb used for culinary and medicinal purposes. It is a hybrid of water mint (Mentha aquatica) and spearmint (Mentha spicata), and can be found widely cultivated in Asia, Europe, and North America. The essential oil it contains is a primary source of menthol, along with the active substances menthone and pulegone.
Used medicinally, peppermint is used as a carminative (relieves flatulence) and antispasmodic. Menthol is also found in soaps, oral hygiene products, fragrances, and mentholated tobacco products.
Peppermint oil is the fifth most-produced essential oil in the world (Schmidt 2009), and it is most widely produced in the United States, China, and India as the leading peppermint-producing countries (Denny and Lawrence 2007).
US peppermint production throughout the 19th century was centered in Wayne County, NY. The oil is harvested by high-pressure steam distillation, where fresh mint would be packed into a retort, and steam is passed through the chamber.
The oil would float on top of the water and then be distilled by different boiling points of water and oil. Newer more modern methods introduced higher pressures, wider ranges of temperature control, vacuum distillation, and crystallization, which has resulted in greater yields, higher quality, and a greater variety of products for specialty applications.
Studies on Peppermint Oil as an Insect Repellant
There have been numerous laboratory studies conducted to evaluate the repellency and contact toxicity of numerous essential oils and other natural pest control methods.
University of Georgia
The University of Georgia conducted experiments on six essential oils and their ability to repel the Argentine ant (Linepithema humile) and the red imported fire ant. Both species crossed barriers that were treated with essential oils, including peppermint, and monitored for results after 24 hours of exposure.
The mortality rate for Argentine ants exposed to peppermint oil was almost 90%, and the results were confirmed in a subsequent study that found 1% peppermint oil to be an effective repellent for Argentine ants, for a period of one week.
That bolded part is an important takeaway because it means that the peppermint oil must be reapplied every week to be continuously effective at controlling ant populations.
South China Agricultural University
Field studies at the South China Agricultural University found that “the repellency and toxicity of peppermint oil particles caused fire ant nests to be abandoned”, and significantly deterred the foraging of red imported fire ants.
Bits of sausage were treated with essential oils of different types, including peppermint oil, and placed near fire ant nests, where cameras were set up to record the ant workers’ behavior towards the treated sausage pieces.
The results found that “the number of worker ants recruited was significantly less than the control when the exposure time is greater than 10 min” in regards to sausages treated with peppermint oil. However, the most effective oil was Capsicum annuum, distilled from chili pepper plants.
Read More: How to Get Rid of Ants
Why Does Peppermint oil Deter Ants?
It’s simple enough to say that ants are repelled by the smell of peppermint oil, but for science buffs, let’s dig a little deeper.
The major chemical compounds found in peppermint oil include terpene, alcohol, and menthol. Each one of those chemical compounds is a natural fumigant, which means that insects and rodents are repelled when their smell receptors pick up on the compounds.
Exactly why they are repelled by the smell of these compounds boils down to evolutionary traits. Insects and plants share a long evolutionary history with each other, which means that plants have developed their own defenses against insects and herbivores from feeding on them.
Terpenes are secondary metabolites widely distributed in the plant kingdom. Plants produce mixtures of terpenes, which are easily isolated by hydrodistillation as oils. The toxicity of various terpene compounds (described as the compound’s LC50) depends on the plant, and some insects have also evolved bio mechanisms for dealing with the toxicity of certain terpenes, but some terpenes remain too toxic for insects to handle.
You can read the rest of the above-linked study on the toxicity of terpenes to insects, but the short version is, plants developed a way to wage chemical warfare against insects, which is why peppermint oil extract is effective at repelling ants.
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- Please note: not suitable for consumption. Keep the product out of the reach of children. Always test the discrete surface before spraying. Wash thoroughly after each use and avoid contact with eyes and skin. Protective equipment is recommended for the eyes and hands. If the product comes into contact with the eyes, wash thoroughly with water.
Other Studies Worth Checking Out
- Peppermint oil on human skin was effective against three mosquito species. From: Ansari, M. A., Vasudevan, P., Tandon, M., & Razdan, R. K. (2000). Larvicidal and mosquito repellent action of peppermint (Mentha piperita) oil. Bioresource Technology, 71(3), 267-271.
- Beta farnesene in peppermint confused aphid phermones. From: Crock, J., Wildung, M., & Croteau, R. (1997). Isolation and bacterial expression of a sesquiterpene synthase cDNA clone from peppermint (Mentha x piperita, L.) that produces the aphid alarm pheromone (E)-β-farnesene. Proceedings of the National Academy of Sciences, 94(24), 12833-12838.
- Of 53 tested plant oils, bay, caraway seed, clove leaf, lemon eucalyptus, lime, pennyroyal, peppermint, rosewood, spearmint, and tea tree oils were highly effective against the greenhouse whitefly. From: Choi, W. I., Lee, E. H., Choi, B. R., Park, H. M., & Ahn, Y. J. (2003). Toxicity of plant essential oils to Trialeurodes vaporariorum (Homoptera: Aleyrodidae). Journal of Economic Entomology, 96(5), 1479-1484.