Ron is cutting a hole in the wall for the vent pipe (chimney) for our new pellet stove. Stuff started spilling out and we realized they were buckwheat. Not hulls, whole buckwheat. And they were used to insulate the house.
Edited to add & clarify: The layer of wall goes like this – newish wallpaper, a recent thin skim coat of plaster, old plaster with hair visible in it, lath (thin strips of wood), buckwheat, boards, blown-in cellulose insulation, outside boards.
No wonder we can’t hear a thing in here. And yes, we have really deep windowsills. 
I’ll add pics as I take ‘em.
Son of Edit: here ya go! It’s like two whole walls.
Wouldn’t bugs come to eat the buckwheat?
Too cool! I would imagine bugs aren’t a huge problem as long as everything is sealed well. The same sort of thing is true for strawbale construction. If it is well-sealed then the straw not only remains bug free, but it stays so fresh that animals have been known to try to eat recently exposed but 100+ year old straw encased in walls.
That’s kinda what we have going on. I mis-typed, they are just buckwheat hulls (outer seed casing), so anything a bug or rodent would want is already gone. Plus they are well-sealed in the walls. The back of the laths look new, that’s how sealed it is. And the stuff is all 100 years old.
It is indeed very cool.
Years and years and years ago we lived in a turn of the century home. When the plaster fell apart in an upstairs bedroom we discovered that the entire level had been insulated with crumpled newspaper. Suddenly it made sense why it was so damn cold up there during the winter.