They have no valve on their bladders, so constantly drip urine wherever they run. This can't be good when they run over kitchen work surfaces
We were lucky because they weren't nesting inside the house, and were mainly just running around in a cupboard where we kept pans and that but no food. We'd find like 3 droppings a week, which in some ways is worse than having a proper infestation cos you can't be sure you've got rid of them