I have mice in a cavity wall - I did have a problem with mice a while ago in the kitchen and it appears my cat then brought them upstairs and they went into the spare room somehow and then burrowed into a hole and made a home. I didn't want to kill them so used live and snap traps and eventually blocked their hole off but went in there the other night and can hear them scratching and squeaking in the wall.
I'm tempted to leave them be but worried what they would do to the cavity wall. They did go on a 'run' through the Victorian cottages in my street... cat now sadly gone so can't use him to help out.
So would you kill or leave? And what damage can they do a cavity wall over time?