Actually... That isn't true and I think the story of how that rumor originated was because of a woman who wanted to prove how easy it was to start a rumor and convince others to see it as fact. And it worked, a little too well...
"In a 1993 PC Professional article, columnist Lisa Holst wrote about the ubiquitous lists of “facts” that were circulating via e-mail and how readily they were accepted as truthful by gullible recipients. To demonstrate her point, Holst offered her own made-up list of equally ridiculous “facts,” among which was the statistic cited above about the average person’s swallowing eight spiders per year, which she took from a collection of common misbeliefs printed in a 1954 book on insect folklore. In a delicious irony, Holst’s propagation of this false “fact” has spurred it into becoming one of the most widely-circulated bits of misinformation to be found on the Internet."
https://www.snopes.com/fact-check/spiders-inside-her/
https://www.snopes.com/fact-check/spiders-inside-her/