The spiders you swallow when you sleep

You've heard this one, right? You swallow x number of spiders while you sleep per night, per year, in your lifetime etc. Every time you hear about it, it's a different number, over a different period of time. Now I'm asking this: what possible study could even be done to determine how many, if any, spiders we consume? I'm sure at some point in our lives we eat spiders while we sleep, but I posit that any statistic on the subject has been entirely fabricated. I just heard Kelly Ripa state it as a fact (8 per night!) and I wondered if it would even be possible to do a real study. If you did it in a sleep study environment, that certainly wouldn't be an accurate representation of the proposed real world scenario. What is up with this bizarre factoid?

And please, if you know of an actual study, I want to know.