Myth: You unknowingly swallow an average of four live spiders in your sleep each year.
Fact: This very widespread urban legend has no basis in fact. It exists in various forms; another common version is that you swallow an average of 20 in your lifetime. (At 4 per year, that would make a very short lifetime of 5 years...) A correspondent in Pennsylvania had heard a version that involved swallowing a pound of spiders (while sleeping) in one's lifetime. (That would be over 20,000 average spiders, for a lifetime of 5,000 years at the 4 per year rate).
For a sleeping person to swallow even one live spider would involve so many highly unlikely circumstances that for practical purposes we can rule out the possibility. No such case is on formal record anywhere in scientific or medical literature. Millions of people have some time or other watched another person sleep; so why don't we have one eyewitness account of a spider trying to enter the sleeper's mouth?
Since this page first appeared, I have heard from one person who found a small harmless spider hiding in her ear (which is possible), two who claimed to have had one in their noses (but had no evidence that it wasn't already in the hanky), and a few who stated that years ago, when they were young children, they spat out or brushed from their mouths an object they interpreted (while still groggy with sleep) as a spider or spider leg. Those stories are so similar they may qualify as a distinct urban legend. Of course nobody ever preserved the evidence, and I remain unconvinced that a spider would visit a huge breathing monster and enter its mouth.
In 2007, news stories recounted a doctor's finding two spiders in a boy's ear. I'm quite sure two spiders didn't end up in the same ear without human aid. The only credible account came from a woman who'd had a ballooning spider blow into her open mouth in a grassy field on a windy day – but that, too, happened when she was a child!