Although ways to kill silverfish and why one should seem a lot more interesting, I suppose that in deference to the original subject of the thread I should confirm that in my area of the US (Kansas):

Children universally called them "rolypolies" - when I was a child.

Virtually all of the adults of older generations that I've known called them "sowbugs."

I can recall a couple of kids that I knew in gradeschool days that called them "pillbugs" but most of us kids figured "they wuz furriners, sort of" and hadn't learned the local linguistic subtleties. I think they were Adventists or somethin' like that, and came from "back east." Maybe Kansas City or somethin'. That's about as far as East went in those days.

I can't really say that the "old-timers" had all that much knowledge of these bugs' placement in the ecological function of things, but I do remember one day when granddad caught me teasin' some with a stick to make them roll in a ball up so I could flip them like marbles, and objected that I ought to "leave them alone and let 'em work."

I think that was the time that he told me that when a horse hair falls in the water trough and soaks long enough it turns into a water snake, so I think I spent the rest of the week watching the hair I pulled out of old Fannie's mane float around in the stock tank.

Never did get a snake out of it, but grandpa said I just didn't wait long enough. Grandpas are strange sometimes.

John