Rattus Norvegicus is the scientific name for the Norway rat. They are classified as a species of least concern due to their abundance in America. They can swim, climb, and burrow while searching for food.

Norway rats constantly explore their environment and memorize everything about it. They don’t have great eyesight, so they depend on their other senses, especially their sense of smell. Anything new to their environment, like a bait trap, may be avoided for days. They are clever; after investigating a trap, they may discover a way to take the bait without tripping the mechanism, absconding with their prize, and frustrating your efforts to make your home rodent-free.

Norway rats can be 16 inches long and weigh up to one pound, they can fit through a 1.5-inch hole or crack. Even if the entryway is smaller, these rodents can easily gnaw around it to make a hole larger.

Norway rats have incisors that constantly grow throughout their lives, averaging 5 inches of growth a year. Rats will chew on any hard materials to keep their teeth filed down. Norway rats can chew through many materials, including aluminum, wood, vinyl, drywall, plastic, mesh, and thick fabrics.

What Is A Norway Rat?

The Norway rat has many aliases, including brown, sewer, street, Hanover, Norwegian, city, water, and wharf rat. Their nicknames are representative of the many environments in which they live. These animals came to America on cargo ships from Norway, but they were originally from Asia. The Norway rat is also a common species used in research laboratories, leading to another nickname: the lab rat.

Norway Rat Characteristics


Norway rats, including the tail, are typically 15-16 inches long. They have short, coarse fur that is either gray or brown and with a lighter shade on their bellies. Males are slightly larger than females. The ears and tails of Norway rats are bald; unlike other rats, their ears do not fold down over their eyes because they are shorter.

Nocturnal Foraging

At dusk, as daylight fades, Norway rats search for food, build nests, and create burrows. Because they are nocturnal, you may not spot a Norway rat during the day, which, in turn, may make it difficult to notice you have an infestation until after the rats have done damage to your property or contaminated your food or water. Pay attention to any noises you hear at night. The sounds of rodent activity can give you advance warning that rats are in the process of compromising your home.


When it comes to food, a Norway rat’s diet is very diverse. Norway rats living in the wild forage for nuts, seeds, grains, mice, small birds, bird eggs, and plants.

Norway rats have adapted well to urban environments, primarily because of their access to human food. Most rats eat food scraps that are thrown out in the trash or brush. Because of the abundance of food scraps, Norway rats don’t need to travel too far for a meal. However, if they don’t find enough food outdoors, they will find a way into your home, contaminating pet food, cereals, chips, and other pantry items.


Within 300 feet of a food source is where Norway rats build their nests, and it’s in a nest where you’ll find their offspring. Norway rats generally live two to four years and can reproduce up to seven times yearly. With each birth, an average of six pups are born. Four months after their birth, females are mature enough to start reproducing themselves.

You can see how quickly an infestation may occur. One female can produce 42 pups in one year, and all the females out of those litters can also produce 42 pups yearly. Hundreds of Norway rats could occupy your home in one year.

Do Norway Rats Live Alone?

Norway rats never live alone. Instead, they live in large groups or colonies, consisting of as few as 15 and as many as 150. Some females may spend time in a nest alone when birthing a litter. However, Norway rats tend to share nursing duties. It is common for females to nurse pups that are not their own.

Norway rats develop a hierarchy, with dominant males and females getting better nesting areas, foods, and sub-groups forming below the dominant species. Colonies are not friendly with each other, and males can become aggressive with Norway rats outside their group.

Where Do Norway Rats Live?

The colonies, if burrowing underground, create numerous tunnels and nesting areas. One area is where they store food, one is where females give birth, one is for nursing and weaning, and the rest are burrows for denning. Norway rats can climb, but they prefer to live below structures.

If a colony is in your home, it is likely in your attic, crawlspace, basement, or walls. If space can’t be found in any of those places, Norway rats will live in sewers, docks, sheds, warehouses, grain bins, silos, and near restaurants.

Damage Caused by Norway Rat Infestation

Norway rats can cause a good deal of damage inside and outside a home. An infestation will destroy crops, contaminate livestock feed, and cause structure instability to anything the rats burrow under, including riverbanks, driveways, homes, and roads.

Norway rats will gnaw through anything they encounter, both under and above ground. They will chew through water pipes, electrical wires, windowsills, doors, and vents. If inside your home, you can expect to see gnawing on drywall and baseboards, shredded insulation, or even nests inside your insulation.

Norway rats also leave greasy smudge marks on walls, floors, and anything their fur touches. Additionally, they can be very annoying due to the numerous sounds they make. If you hear chirping, squeaking, squealing, clawing, grunting, climbing, and fighting noises, it could be a group of Norway rats.

Like all other rodents, Norway rats leave trails of urine and feces as they travel. Droppings can be ¼ of an inch long, and the mold spores that grow on them can affect humans. Norway rats carry diseases that can be transmitted to humans through a bite, such as trichinosis, salmonellosis, and rat bite fever. Hantaviruses are the most dangerous diseases rats carry. Among many symptoms, humans develop severe respiratory infections when exposed to these viruses.

Because ticks, fleas, and mites live on rats, you become exposed to the diseases these insects carry too, such as Lyme disease and Typhus. Indirect and direct health risks come from bites, inhaling mold spores on droppings, touching urine or feces with your bare hand, or eating foods the rats have contaminated.

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