Do Chestnut, Lemon, or Peppermint Scents Repel Spiders?

The internet suffers no lack of suggestions for methods to repel common household pests, and that sheer volume of claims makes scientific testing of such repellents all the more valuable.

Entomologists, of course, are here to help. Adding to a long line of tests on all varieties of household pest repellents, a new study published in December in the Journal of Economic Entomology puts three natural compounds to the test for their efficacy in repelling spiders.

“My personal research interest is in finding repellents to repel spiders out of the homes of arachnophobic people, to reduce the amount of pesticides used,” says Andreas Fischer, a masters’ student in the Department of Biological Sciences at Simon Fraser University and lead author on the study. “So, we thought to test the three most recommended folklore for spider repellents in hope to find something.”

Fischer—along with colleagues Manfred Ayasse, Ph.D., at the University of Ulm in Germany and Maydianne CB Andrade, Ph.D., at the University of Toronto Scarborough in Canada—tested the top three substances cited in online search results as natural spider repellents: lemon oil, peppermint oil, and chestnuts. To see how spiders reacted to each substance, the researchers conducted choice tests with adult females of three spider species: Latrodectus geometricus (the brown widow) and Steatoda grossa (both of the Theridiidae family) and Araneus diadematus (Araneidae family). All three are common in or around human dwellings in Europe or North America.

The choice test consisted of a Y-shaped tube, with a test substance in one arm of the forked end and no substance (i.e., control) in the other fork; a spider placed in the central tube was recorded as having made a “choice” if it entered and remained in either of the other two arms of the tube for at least 30 seconds.

Results were mixed: Both chestnut and peppermint oil showed apparent repellent effects on Latrodectus geometricus and Araneus diadematus, with the two species avoiding those substances in more than 75 percent of tests, but they did not have any significant effect on S. grossa. Meanwhile lemon oil, though having appeared most frequently in the team’s online search results, did not have a significant effect on any of the three species.

All three spider species tested are mostly sedentary as adults; they build their webs and then generally stay put. Thus, Fischer’s team notes, any repellent effects found in the experiment can only be said to keep spiders from entering an area; they may not induce the same spider to leave an area if it has already settled in. The question also remains as to whether other common species of household spider would be similarly affected.

“We are currently conducting a much more extensive study,” says Fischer, “in which we also test in what way such repellents affect the location for web-building and, in a second step, if repellents can be strong enough to cause a spider to leave her web and relocate. We also plan to identify the specific semiochemicals that cause the repellency.”

For the average consumer, the results offer some evidence to the potential repellency to spiders of chestnut and peppermint oil, but they cast some doubt on that of lemon oil. But, for the entomologist, more questions abound.

“Future studies can try to understand what the ecological reasons for this behavior might be,” says Fischer. “For example, if these semiochemicals occur in other natural contexts spiders generally avoid. Or, if these semiochemicals have physiological effects that might be even toxic.”