Strange things with grubs inside

[Tony F Dordogne]

A couple of chums have found hard brown, almost cement like structures, about an inch long, single chamber, which have contained small spiders and grubs which are feeding on the spiders.  I found one on the inside of one of my compost bins a few days ago, the grubs (two chambers) were large, about 3/4 inch and they were feeding on the small insects inside the chambers.

I don't have a problem with them in the garden but my chums have found them in their homes, usually fixed to cushions and other soft furnishings.

The structures are really hard and when broken open, they crumble like old cement.

Any ideas from anybody what these may be?

[Patf]

Some kind of wasp perhaps? The wasp larva looks like a grub.