Norway rats can undermine building foundations and slabs with their burrowing activities and can gnaw on all types of materials, including soft metals such as copper and lead, as well as plastic and wood. They also damage garden crops and ornamental plantings.
Norway rats tend to remain in hiding during the day and are not usually seen exposed unless driven out of their hiding spaces because of limited space or disturbances. Sightings during the day often indicate a potentially large infestation.
Outdoor burrows surrounding the building may be an indication of Norway rat nesting. Other signs of Norway rats are their gnaw marks on food and objects such as utility lines. Rub marks or grease stains caused by rats running along an edge also can indicate activity. Generally, darker stains indicate greater activity. Perhaps one of the best indicators is their droppings. Norway rat droppings are blunt capsule shaped and are about 7 to 7-1/2 inches long. They can be scattered along frequently traveled rodent pathways.