Myth: "Hedge apples" (Osage orange fruit) or horse chestnuts can be used to repel spiders.
Fact: The story that the fruit of the Osage orange tree (also called hedge apple, monkey ball, or spider ball) can repel or ward off spiders turns out to be extremely widespread in Midwestern states, where the trees are common. Details vary, but in general it seems that people put these aromatic fruits around their walls in fall to "keep spiders from coming in." Since house spiders don't actually come in from outside, of course this works just fine, but there is no evidence that spiders are repelled by Osage oranges. They live on the trees and even make webs on the fallen fruit. What's more, spiders seldom show any sign of being able to detect airborne odors!
In some versions of the story, the repellent effect has been transferred from spiders to cockroaches, mosquitoes, chicken mites, or mice. Since squirrels regularly chew through these fruits to get the tasty seeds inside, a rodent repellent effect seems pretty unlikely. A recent study did find some cockroach repellency in a purified extract from the fruit – but not in the whole fruit.
Horse chestnuts, Aesculus hippocastanum
Photo: Rod Crawford
In the Pacific Northwest, where Osage oranges are seldom seen, the legend has been transferred to horse chestnuts. I like horse chestnuts and usually have some around, but still have plenty of spiders, so I know of my own experience that this doesn't work.
In the 21st century, peppermint oil has been widely promoted as a sure-fire house spider repellant. No research supports this, though spiders may possibly be reluctant to walk on treated surfaces. A 2012 study found that planting peppermint in orchards decreased herbivore abundance, but had no effect on spiders.
A correspondent in British Columbia has heard a version of the myth in which the spiders are repelled by copper pennies! All these stories show the power of placebo effect. You set out the magical objects; house spider mating season ends; and hey, it worked!