Thats great news. Do you make a depression under the slabs and put nesting material in the depression ?
Very simple idea, but I guess the only problem is that you cannot check if they are occupied very easy or status of the nest compared with a box and lid.
Are they just occupied by the queens at the moment ?
Yes there is a depression the size of a football with a crumpled up piece of wire mesh for drainage with dry moss on top of it.I will do another topic with a photo attached to show you better how the nests are constructed.Both nests have workers going in and out.