Written by Raymond Nakamura
Once upon a time, Raymond earned his doctorate studying the hydrodynamics of sand dollars. Nowadays, when he’s not employed as personal assistant to his lovely and demanding daughter, he enjoys creating fun and educational experiences in science and history using facts and fiction, words, pictures and whatever else is handy. Follow him on Twitter @raymondsbrain


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Sunday, October 2, 2011 - 1:56pm

Do horse chestnuts keep spiders away?

While walking our kids to school one morning, I yakked with another Dad about the recent abundance of spiders (he was pulling a web from his hair). He said, "We put chestnuts around our house to keep spiders away." I'd never heard of this before. He acknowledged the weirdness of the idea but insisted on its efficacy.

I crawled around the Web and found various versions of this kind of spider repellent, not only chestnut but also horse chestnut, walnut, or the large round fruit of the Osage orange tree. Still others suggested it was the wood, not the nut or fruit. I did not come across anyone mentioning the spikey casing still on. Maybe people with arachnophobia would just like to believe it would be that easy to keep spiders away.

In Britain, the notion may be more widespread. Their Royal Society of Chemistry held a contest to find the best evidence for or against the idea that spiders dislike conkers, which is what they call horse chestnuts.

The winning entry came from a grade five class from Cornwall. They showed that their spiders did not seem concerned about walking over conkers compared to other materials.

They were lauded for their efforts and sure it's great that they aren't afraid of spiders, but kids these days seem to get patted on the head for every little thing. I did not expect horse chestnuts to have any effect on spider behaviour, but I'm not sure the idea was tested sufficiently, as the Ranger's Blog has pointed out.

1. Not all or even many of the spiders tested would occur in a house. So if the question is whether horse chestnuts keep spiders out of your house, it might be useful to find spiders that would be in your house. Here are some notes about some misconceptions people might have about spiders in BC.

2. Harassing the spiders may not be a suitable test of their substrate preferences. It would take longer, but it seems like you'd have to wait to see what spiders do over time. Something else I hadn't realized before was that household spiders aren't coming in from the cold and you aren't doing them any favours by putting them outside.

3. Horse chestnuts are inedible, which may support the idea that they contain some chemicals noxious to spiders. Some have suggested you need to open the chestnut up or poke holes in it to take effect.

Even if it turns out that horse chestnuts or these other items do not have any effect, I am intrigued as to why people would believe this in the first place. I can imagine a situation where you might happen to have conkers around at the this time of year and the spiders disappear for other, perhaps seasonal reasons.

I have horse chestnut trees all down my street, and I don't have many spiders in my house. If you have a lot of spiders in your house and would like to test chestnuts on them, then let me know in the comments and maybe we could collaborate.

Comments

I've used the chestnuts,

I've used the chestnuts, spikey things off and seems to work. Also have found that peppermint oil sprayed around doors, windows etc, have kept them out. There are a lot of things you can use that are not harmful to kids or pets.

I think it's to do with a

I think it's to do with a chemical in the chestnut wood, not the chestnut itself. I've never heard anything about chestnuts keeping spiders away, but I HAVE heard that they won't attach their webs to chestnut wood beams. Maybe that's the source of the story?

Horse chestnuts are different

Horse chestnuts are different from regular chestnuts. .. they are poisonous to humans and animals if ingested. .. while regular chestnuts are entirely edible... therein lies the difference. ..

I've tried chestnuts, with

I've tried chestnuts, with holes drilled in them, with zero effect. The spiders will even attach webs to them. I suspect the effecacy of chestnuts is more of a seasonal coincidence. By the time the chestnuts fall, the worst of the spider invasion is over.

Oh my gosh really. Apparently

Oh my gosh really. Apparently everyone says it works. Should I try it????

I live in the countryside and

I live in the countryside and I have had a huge amount of spiders this year, couldnt find conkers, i have now. i had very few last year due to putting conkers in places they tend to enter, ive found it really helps!

I am 90% sure that chestnuts

I am 90% sure that chestnuts work on spiders because I have tried successfully and it worked. Maybe there is a chemical in them that keeps them away.

When we first moved to BC

When we first moved to BC someone told us about chestnuts being able to rid a house of spiders. We have chestnuts in wicker baskets all over the house, garage and crawl space. Does it help - well, our neighbors have spider problems and we don't - so, we will keep putting chestnuts in our house.

I know from trying it that

I know from trying it that horse chestnuts do not work. I also had recommended to me peppermint oil, which I'm trying now, however, looking on the net, there are many brands of non-harming spider repellent which I'm about to try out- I don't mind the spiders, but their webs are a nuisance in my workshop!

I have used conkers around my

I have used conkers around my house last 2 years! Used to get massive spiders everywhere.....judder, judder!! Since using conkers I've not had even one big spider! They have had no effect on harvester spiders though, although I can tolerate them!! :)

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