I'm not entirely sure why anyone would want to exclude spiders from their home, my preference would be to have a flyeater in each corner of the room to eat the flies. Flies spread disease. Spiders modulate Diptera activity.
Anyway, every autumn, the deceived wisdom that putting conkers, the glossy brown seed of the horse chestnut tree, Aesculus hippocastanum, around your home will scare the spiders away comes up. It's evergreen content for columnists. But, it is a myth, it has been debunked several times over the years. I have been trying to find the origins of this particular piece of pseudoscience to no avail. Most searches simply bring reference up to an old publicity campaign by my work alma mater, the Royal Society of Chemistry which ran a competition to test the hypothesis and rewarded some primary school kids who demonstrated that the conkering theory is bonkers.
A search of PubMed brings up a paper from one Jane Bates who writes for Nursing Standard, in 2009 she mentioned that her friends thought it hilarious that she puts conkers around her house to ward off spiders. And, well they might, like I say, it's deceived wisdom. There are no anti-arachnid chemicals exuded by conkers and if anything spiders adore conker trees, you will find numerous species weaving their webs among the spiny danglers.
Of course, the seeds of the horse chestnut tree do produce natural products, all living things make chemicals. Extracts from the horse chestnut are already used by the pharmaceutical, food supplement, and cosmetic industries. The active components are saponins of the oleane type, but the seeds of this tree also contain flavonoids, specifically glycosides of quercetin and kaempferol.
A study published in August 2018 detailed the virucidal and broad-spectrum antiviral activity of one such compound from the seed, beta-escin. This chemical modulates cytokine production depending on the stimuli (viral or non-viral) and the cell type under study [Michelini et al., J Pharm Pharmacol (2018); DOI: 10.1111/jphp.13002]. Escin is actually a mixture of triterpenoid saponins and earlier in the year another team discussed the anticancer, anti-proliferative, pro-apoptotic, and anti-inflammatory effects properties of these compounds [Cheong et al., Cancer Lett (2018) 422:1-8. DOI: 10.1016/j.canlet.2018.02.027].
As ever, there is a materials science link. In 2014, researchers isolated starch from conkers and demonstrated it to have a maximum decomposition temperature of 317 degrees Celsius. Processing of this starch with glycerol and melt blending gave them a thermoplastic material, which they describe as having "exhibited adequate mechanical and thermal properties". [Castaño et al., Carbohydr Polym (2014) 4;112:677-85. DOI: 10.1016/j.carbpol.2014.06.046].
At a time petroleum-derived plastics seem to be accumulating at a worrying rate in our environment, in landfills, and the seas, biodegradable materials of sustainable origin might offer an alternative. Given that starch is a biodegradable raw material perhaps the seed of the horse chestnut could become the conkering hero. But, if it does, what are all those children who bake their conkers and dangle them from strings for the classic school playground play off of "conkers" going to do each autumn if the sustainable chemical industry brigade have hoovered up the arboreal droppings for their own purposes? And, then there's the arachnophobes...well, they can seek therapy and make their homes fly-free zones instead.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.
Footnote. After reading this article, a friend reminded me that British children were encouraged to collect conkers during World War II as they were a good a source of starch for making acetone and thence cordite at a time when food starch was in short supply. It was Professor Chaim Weizman at Manchester University who worked out how to make acetone from conkers. Of course, he later became the first president of Israel. More here.