The Norway rat is the largest of the commensal rodents. The head and the body of the Norway rat is 7 to 10 inches long and the tail is about 6 to 8 inches long. The body weighs about 7 to 18 ounces. The ears and eyes are small and the muzzle is blunt. Their droppings are 3/4-inches long with blunt ends. The adults are sexually mature in 3 to 5 months. The female Norway rat produces 3 to 6 liters per year. The adults may live from 6 to 12 months. They have very poor sight but have great sense of smell, taste, touch, and hearing.