I couldn’t find any persuasive evidence that spiders avoid conkers, so decided to put this claim to the test, says Phil Gates.
Advocates suggest that spiders are repelled by natural detergents called saponins in the seeds. These are toxic compounds, present in many seeds and leaves, but because spiders don’t eat plants any effect on them would most likely be through external irritation of their sensory system.
I tested this on the daddy long-legs spiders Pholcus phalangioides that live behind our settee. I lined half of the bottom of a small tank with crushed leaves of soapwort Saponaria officinalis, which contain very high concentrations of saponins.
When I introduced the spiders they had no preference for either end of the tank, showing no response to leaves leaking saponin-laden sap, so it seems unlikely that the same compounds inside a conker would have any impact.