• Gnaw marks. New gnawings or holes tend to be rough whereas, old gnawings are smooth from wear and old holes are often greasy.
• Fresh droppings are soft and moist whereas, old droppings are dried and hard; adult Norway’s about 3/4″ (18-20 mm) with blunt ends vs. adult roof’s about 1/2″ (12-13 mm) with pointed ends.
• Tracks/footprints. Front foot 4-toed and print is in front of usually longer hind print with 5 toes. Fresh tracks are clear and sharp whereas, old tracks are at least partially obscured by dust.
• Rub marks or dark, greasy markings on vertical surfaces. Fresh marks are soft, greasy, and easily smeared whereas, old marks are with the grease dry and flaky.
• Found in earthen banks, under concrete slabs, and under walls. If active, free of dust and cobwebs. Main opening usually with hard packed soil, rub marks may be visible.
• Consistently follow same paths, usually along walls, stacked merchandise, etc. Active runways with greasy appearance, free of dust and cobwebs, with fresh tracks and/or droppings.

Damaged goods. Norway rats prefer meat, fish, and cereal (dry dog food a favorite) whereas, roof rats prefer fruits, vegetables, and cereals.