The 'Grit Experiment' by pjames link below is what Barbara is referring to. It was a simple experiment to test whether grit is beneficial in a worm bed. I think he concluded that grit did not help. It was not a very scientific experiment. It was done out of curiosity.

My takeaway is grit is not necessary for worms to reproduce and do well. Apparently many vermicomposters do not add grit.
However, grit may be beneficial, and certainly not harmful. Worms have gizzards and grit is in abundance in their natural habitat.

If grit is beneficial and should be added to the bn, some questions I would have are:

1. What kind of grit is best (soil, rockdust, sand, ect.) ?
2. How much grit do I add, and how small does it need to be?
3. How often do I add grit?
   4)Does grit help with digestion yielding more castings?
4. Does grit result in greater reproduction?
5. Why do I not recall a thread about bin trouble, where the advice given was to add grit? I rarely see add grit advised other than some soil when starting a new bin. I think that is to add microbes.

I really don't have any experience going gritless. I am a itty bitty grit worm farmer, with open bottom bins and dirty horse manure. I do not intentionally add grit, it is just there.
I do wonder why these very old castings have grit exposed (white specks of soil) rather than embedded in the cast.

Good luck, Pete

Here is a link that might be useful: Grit Experiment

I was thinking that was the advantage of using egg shells.