No, conkers almost certainly don’t keep spiders away. Despite being a centuries-old household tradition, particularly in the UK, the idea that placing horse chestnuts around your home repels spiders has no strong scientific backing. When researchers have put it to the test, spiders show no fear of conkers and will happily crawl right over them.
What the Experiments Actually Found
The most well-known test of the conker theory came from a challenge issued by the Royal Society of Chemistry. Primary school pupils at Roselyon School in Cornwall designed their own experiments to settle the question. They placed spiders in boxes alongside conkers and stones, then watched what happened. Most spiders climbed directly over the conkers without hesitation. In another test, spiders in a water tank were given a choice between escaping across a wooden bridge or a bridge made of conkers. Most chose the conker route. The Royal Society of Chemistry declared the results had “finally disproved the age-old theory.”
The folk belief held that spiders were frightened by either the shiny surface of conkers or their distinctive smell. Neither turned out to be true in controlled settings.
One Study Found a Partial Effect
The picture isn’t entirely black and white. A peer-reviewed study published in the Journal of Economic Entomology tested the three most commonly cited natural spider repellents: lemon oil, peppermint oil, and chestnuts. Researchers used a two-choice setup where female spiders could move toward or away from each substance. Chestnuts did strongly repel two of the three species tested, including the common European garden spider. However, the third species showed no response at all.
This suggests that certain spider species may detect and avoid chemicals in horse chestnuts, while others are unbothered. It’s a far cry from a reliable household repellent. The spiders you’re most likely finding in your home in autumn, common house spiders and cellar spiders, weren’t among the species tested. So even this partial evidence doesn’t tell us much about the exact situation most people are trying to solve.
Why Spiders Appear When Conkers Fall
Part of the reason this myth persists is timing. Conkers drop from trees in September and October, which is exactly when spider sightings inside homes spike. But the spiders aren’t arriving because conkers have stopped protecting you. Two separate things are happening at once.
Autumn marks mating season for many spider species. Males that normally stay hidden begin roaming actively in search of females, which makes them far more visible. At the same time, dropping temperatures push spiders toward the warmth and shelter of buildings. Their prey (flies, mosquitoes, and other small insects) also migrates indoors as the weather cools, and spiders follow the food. Rainy spells accelerate this pattern even further. So putting out conkers right as spiders are most motivated to come inside sets you up to think the method has failed, or, if you see fewer spiders by chance, that it worked.
What Might Actually Help
Peppermint oil showed the most consistent repellent effect in that same two-choice study, strongly deterring two of the three spider species. Diluting peppermint oil in water and spraying it around window frames and doorways is a common recommendation, and it has at least some experimental support. The effect fades as the scent dissipates, so you’d need to reapply regularly.
Physical barriers tend to be more reliable than any repellent. Sealing gaps around doors, windows, and pipe entries removes the routes spiders use to get inside. Reducing clutter in corners and along baseboards eliminates the sheltered spots they prefer. Keeping outdoor lights off at night, or switching to yellow-tinted bulbs, attracts fewer flying insects to your walls, which means fewer spiders following them in.
A Safety Note About Conkers and Pets
If you do scatter conkers around your home, be aware that horse chestnuts are toxic to dogs and cats. They contain compounds that cause gastrointestinal irritation, with symptoms including drooling, vomiting, and diarrhea. Larger amounts can lead to more serious problems: loss of coordination, muscle tremors, and in rare cases, seizures. The seeds are also the right size to cause a bowel obstruction in smaller dogs. If you have pets that chew on found objects, conkers on the floor are a genuine hazard, even if they’re not much of a spider deterrent.