I am living at 1000 ft in Tuscany and our appartment has several small lodgers. Sealed tubes, about 1.3cm long and .3cm wide, made out of dried mud. They are often stacked together, then four or five are themselves incased together in a second sking of mud. I have seen large, articulated wasplike insects, and also a massive black bumble type bee taking interest in these shells. Every now and then we find one on the bed, or stuck to a book. Today I accidentally broke two of them when removing them from an item of furnture. Inside were several dead siders, and, perhaps (?) a tiny wasp. I say dead, perhaps they are just inert. I now have them in a glass with a pierced cling film top, to see what developes. Any ideas?
These are likely to be the mud cells of a eumenid wasp, the spiders are food for their larvae. Few species utilise spiders as prey - I will read up and see if I can come up with a likely species.
The large black bumblebee you mention will almost certainly be a Xylocopa species aka a Carpenter bee. These are not bumblebees but a species of solitary bee that nest in soft decaying wood, hence the carpenter name.