(Horrible title, sorry - I just can't think of a better way to word it.)

Over in this thread, /u/historiagrephour was answering a fascinating question regarding beliefs about women on ships during the Age of Sail when this came up (quoting from /u/historiagrephour):

This effect of female nudity over nature was recorded by Pliny in his encyclopedic Natural History (Book 28, Ch 2) where he wrote that a menstruating woman who uncovers her body has the ability to scare away hailstorms, whirlwinds and lightning. If she walks naked around the field, caterpillars, worms, and beetles will fall off the ears of corn. And, even when not menstruating, a woman can still lull a storm out at sea by stripping down to nothing.

Historically, there are a lot of beliefs surrounding menstruation that contemporary people would charitably call "unusual," but there's usually some trail you can follow to a logical conclusion. The Biblical concept of uncleanliness during menstruation, for instance - I can understand how someone could "logic" that out.

Take another snippet from the comment made by /u/historiagrephour:

...a number of ships' figureheads were bare-breasted female figures. It was thought that her open eyes would lead the ship to her destination while her bare breasts would shame the sea gods into calm.

This, too, is from Pliny's Natural History - and I can "logic" this one out. I probably wouldn't have gotten there on my own, but I can see how someone could think for a bit and arrive at the idea that a bare-breasted figurehead would keep the sea shamed into calm.

That first one baffles me, though. Pliny basically describes bare-chested women on their period as a subdued version of Storm from the X-Men, plus some Orkin pest control powers. Surely - surely - there was not empirical evidence to indicate that menstruating women held the power of death over corn pests.

How in the world did this belief take hold so firmly as to make it into Pliny's Natural History as apparent fact? I sort of think of Tecumseh's Eclipse when I ask this question - was there some sort of event that led to this particular belief about the power of menstruation? Maybe a menstruating Roman woman of whom I'm currently unaware once stepped onto her balcony as a hailstorm coincidentally retreated and ... beetle season ended? How the heck did people of the time come to believe this?