The Norway rat (Rattus norvegicus) can grow to twice as large as the Roof rat. They have a thicker, heavier body, a shorter tail and they have a more blunt snout. They are usually browner in color than Roof rats. Norway rats prefer to live at ground level, hence their presence in the sewers. They range 50-150 feet in their search for food and shelter. Females produce 6 to 12 young in each litter and have 4 to 6 litters per year. Like all rats, they have poor vision, and rely primarily upon their sense of smell and their highly specialized senses of feel and balance to survive.

As with all rodents, their teeth grow continuously, and thus they gnaw on many surfaces to wear down their teeth. They can chew through almost any material including masonry, steel, plastic, electric cables, water pipes, etc. posing a threat of flooding