Think of all the debris lodged in a neglected drainage system. Leaves, twigs, pine needles—these are the building blocks that mice and other rodents rely on for their nests. It's no wonder that, particularly in the fall and winter, gutters often play host to mice seeking cold-weather refuge. The real trouble begins when, with their tendency to chew through wood, mischievous mice find their way indoors. One or two may be manageable, but it's a cause for alarm if your gutters become a freeway for dozens and dozens of rapid-breeding rodents. Your best bet? Fill cracks, holes, and gaps in the building envelope, and rid your gutters of any material that may be providing a warm welcome to pests.