The answer to 'why is my mouse trails' is that mouse trails are caused by the oils and dirt from the mouse's feet leaving a visible path on surfaces. This is a common sign of an active mouse infestation in your home. Mouse trails are typically seen on floors, walls, countertops, and other smooth surfaces where the mouse frequently travels.
Some common symptoms of mouse trails include seeing the actual trails, as well as signs of chewing, droppings, and nesting materials. Mice are nocturnal, so you may also hear scratching or scurrying noises at night. Mouse trails can lead you to where the mice are entering your home and nesting.