The case of the strange caterpillar

Have got about 80 of these on the walls and ceiling of the spare bedroom. They are about 8 - 9mm long. The case appears to be attached to the surface at a single point. The grub extends itself approx half way out of the case, but withdraws back in when there is movement nearby.

Douglas thinks they are Tinea pellionella (case-bearing clothes moth). I am going to rear some on to try and confirm this. Will attempt to feed them on bits of wool.