I'd be concerned about it heating up in the bin. If it was composted first, it would be great bedding. I guess the C:N ratio for hay varies, depending on the type of hay, so it is hard to say whether it would be good bedding.

I use hay a bedding. Well actually it is mixed in with the manure from our horses. Depending on how wet you bin is I would wet it and maybe let it dry out for a day or 2 before adding it. It will take a while to break down more than newspaper. As far as depth goes add a little at a time I would say an inch or 2 and you should be fine.

Thanks for sharing your experiences. I will soak the hay first and put it in the worm bin.

See my post on worms, worms everywhere in hay--