Norway Rat | Nebraska Invasive Species Council

Photo: © nm321, some rights reserved (CC-BY-NC)

General Information

Species Name: Rattus norvegicus

Also Known As: brown rat, sewer rat

Family: Muridae (Old World Mice/Rats)

Origin: China

Why Is It Invasive?

Norway rats often live alongside people and can contaminate and consume food, damage infrastructure through burrowing and gnawing, and can transmit diseases to people.

Identification and Ecology

Physical Description

Norway rats can grow nearly two feet long, with their tail equal in length to their body. They can weigh as much as 2lbs and males usually are slightly larger than females. Norway rats dense short fur covering their body except for their tales, nose, and ears, and coat colors range from gray to brown.

Life Cycle

Norway rats live for about 2 years and females become sexually mature around 4 months of age. Each litter has an average of 8 pups and gestation lasts for 22-24 days. Pups will leave the nest between 3-4 weeks of age. One female is capable of having 8 litters annually.

Behavior

Norway rats live in large colonies that are typically male-dominated. They are nocturnal, are excellent climbers, and can fit through holes 1/2 inch in size. When infesting homes they will usually be found dwelling in basement or ground floor areas.

Diet

Norway rats are omnivorous and have a huge range of foods they will consume, but they prefer fresh meats and grains.

Habitat

Norway rats can be successful in a variety of habitats, but are often found alongside humans.

Photos

Brown rat eating a slice of apple on a wooden surface.

Credit: Ed Freytag, City of New Orleans, Bugwood.org

Brown rat on dirt near a wall with scattered greenery.

Credit: Ed Freytag, City of New Orleans, Bugwood.org

Brown rat on a wooden floor against a plywood wall.

Credit: Ed Freytag, City of New Orleans, Bugwood.org

Signs of Infestation

Gnawing

Norway rats gnaw on wood, chords and wires, and storage containers. You may notice holes in food containers, or small, multitudinous teeth marks on harder surfaces. You may even notice small pieces have been removed from meats, fruits, and other fresh foods that are left out on countertops.

Burrows

Norway rats will create burrows next to building or along fences.

Squeaking, Scratching, and Gnawing Sounds

Norway rats communicate to each other through squeaky vocalizations, which you may hear if it is quiet enough. You may also hear them gnawing on wood, chords, and other solid surfaces or hear their claws scrape floors as they move around.

Droppings

Norway rats may leave droppings in areas they have inhabited.

Photos

Damaged wall corner with peeling drywall and carpet debris.

Credit: Liz Kasameyer, Johns Hopkins School of Public Health, Bugwood.org

Norway rats will chew through hard substances and damage structures.

Rodent burrow near fence and bait box on grassy sidewalk edge.

Credit: Gary Alpert, Harvard University, Bugwood.org

Rats will create burrows along fences and next to homes.

How Do They Spread?

Norway originally arrived to North America in the 18th century on trading ships. Since, they have been highly successful at establishing across the continent through human intervention and natural expansion.

Distribution

Norway rats are widespread across the United States and are now a common pest. They can be found in urban and suburban areas.

Control

While many control methods can be performed by individuals with no special training or credentials, consider calling a professional pest management company for large infestations or if you are not comfortable performing the control methods on your own.

Cultural

Cultural methods are primarily preventative and will need to be implemented in conjunction with mechanical methods during an active infestation.

Practice good sanitation to prevent attracting house mice into your home. Dispose of food waste in a tightly closed garbage or compost container and remove food waste from your home regularly. Clean up around pet food areas, remove old fruits and vegetables from your home, and properly store food in sealed containers.

Manage around your home that are well-suited for house mouse shelter by cutting lawns short, keeping gardens tidy, and sealing homes, sheds, and outbuildings. Keep equipment at least 18 inches off the ground if able. Consult a home construction company regarding rodent-proof construction.

Mechanical

Once an infestation has occurred, population reduction is almost always necessary. Utilize humane methods like wooden snap traps or rodenticide traps. Many traps and baits can purchased at hardware stores. Place baits in areas with evidence of mice activity. Be sure to place traps in areas away from children and pets and carefully select the method that is best-suited for your home's safety needs.

Electronic devices are typically ineffective, as rats quickly adapt to repeated sounds. Predators like cats and dogs are typically also no effective at population control.

What to Do if Sighted

If you see signs of Norway rat infestation in your home, refer to the above control methods and implement a control program promptly. Wear personal protective equipment like rubber gloves and a face mask when cleaning areas that have been inhabited by Norway rats and when removing deceased rats. Wet droppings, urine, and nests thoroughly with a household disinfectant before cleaning. Remove and dispose of foods that have been contaminated by Norway rats and thoroughly clean areas that have been inhabited for using.