...squirrels in my house

Okay - they're not really in my house but they are in the basement. The furnace guys told me that I have a friend who was heard scurrying through the basement walls and crunching walnuts, Now, I'm all for animal rights but this is my house...squirrels live outside, in the woods, in trees, where there are plenty of nuts and twigs and things to make nests. Some action must be taken! Just wait 'til Steve gets home!