Just found woodworm in the floorboards and joists in the understairs cupboard while laying some wiring and under further investigation it has spread to the floor boards and joists in the hallway. One of the joists sounds dead and is quite spongy. I've no idea if the worm is still active or if it's long standing damage, Is there any way to tell, there is some wood dust below the damaged areas but that could have been there for years. How serious a problem is this, do I need to treat the whole house immediately or can I just treat the effected area's which at the moment is easily accessible and then treat the rest of the house as I decorate in the next year or so.