Norway Rat

(Rattus norvegicus) is also called sewer rat, brown rat, water rat, wharf rat, and gray rat. It is found in all the states in the USA, but in coastal states, the Roof Rat is more dominant.

These “super rats” can reach 16″ in length. Each female rat can give birth to 20 pups in her lifetime. Some factors affecting rat populations in cities include continuously mild winters, weather-related disasters, and encroachment of their habitats by new urban development.


The Norway rat is larger and more aggressive than the Roof Rat. As an adult, the Norway Rat can weigh between 12-16 oz. with a body length of 6-8 inches long. The nose is blunt with small ears, and small eyes. Its fur is shaggy and coarse with variation in colors. The tail of the Norway rat is shorter than the head and body combined, and scale-like. The standard method of identifying the difference between a Norway rat and Roof rat is pulling their tail back over the body. The tail of a Norway rat can not reach its head.

Inspecting Norway Rat Infestation

Inspecting Norway Rat Infestation

Their droppings are usually a shiny black but may vary according to their diets. The Norway Rat droppings are 1/4 to 1/2 inch in length. The droppings are capsule shaped and have blunt ends.

  • Norway Rats and Roof Rats will leave a hind foot track of about 3/4-1 inch where a mouse’s track measure’s 3/8 of an inch or less.
  • Norway Rats will leave a mark as they drag their tails between their feet. Using unscented baby powder or flour can be dusted in areas of suspected activity. Lightly use the powder in these areas.
  • Norway Rats can leave gnarled hole about 2 inches in diameter. The holes have rough edges. Their preference is to gnaw on wood but will gnaw on electrical wiring causing damage.
  • Rat burrows can be found along foundations, or beneath rubbish and shrubbery. If the burrow is active it usually clear of vegetation. Rat runways are smooth and well packed. Indoors, these runways

Norway Rats Diet

Norway Rats will eat a lot of types of food but prefer proteins and carbohydrates. Food items from a house-hold garbage can provide these rats with a balanced diet. They will eat meats, fish, cereal grains, livestock feed and fresh fruits. Norway rats that live outside may feed outside or enter buildings at night daily for food and return to their outside habitat burrows after feeding. These rats will kill and eat various small reptiles, mammals, birds and insects.

Unlike mice, they need water for survival. They require the 1/2-1 ounce of water daily if they feed on dry foods. If they are in and around buildings, they can get their water from toilets, sinks, water off condensing utility pipes and rain puddles.

Norway Rats Habits and Biology

The mating and gestation period is about 22 days. Female pups reach sexual maturity in 2-3 months with an average of 8-12 pups per litter and 4-7 litters a year. The young rats are naked and blind at birth, with their eyes opening in about 9-14 days. Adults live about a year and prefer to live in colonies. They may breed all year long, but breeding peaks in the spring and fall of the year.Breeding will decrease during hot summers or cold winters for outside colonies.The average rat lives


The Norway rat prefers to live in underground tunnels or burrows. New rat populations have short (between 12-20 inches long)of burrows, but as the population grows and they mature, the burrows are enlarged. They can have many burrows interconnected, forming a network of underground tunnels. These ground burrows usually have one central opening that they use for an entrance or exit, and a couple of holes that are used for escaping. Several distinct rat families may use the same runway and the same food and water sources, sharing an extensive burrow system. As the rat population increases and if food/water sources are limited, fighting will begin as they defend territories. These fights will result in dominant rats that are the first to feed. Rats prefer to feed at night and are mostly nocturnal. The subordinate rats are forced to reside in a section of the burrow that is further from the food/water sources. These subordinate rats will feed and be active when the primary dominant rats are not active. That is why you may see rats during the day time, which indicates a large population.

When using rodent baits in burrows and outside, the dominant rats are often killed first, with bait shyness developing in a few “smart” rats. As with other rats, Norway rats are suspicious of changes in the environment. This suspicion makes baiting or trapping a little tricky. It may take a few days of undisturbed bait or traps to be trusted enough for them to approach them. See rat baiting tips while using bait stations..

Nests and Territories

They can be found near food sources such as barns, granaries, silos, and livestock if found on farms. If found in urban areas, they can be found in the ground in yards or any available ground space. In most cases, they will be found in underground tunnels but may also live inside buildings their whole lives. Norway Rats can enter homes during the night, seeking food, then return to burrows. If found inside, Norway Rats usually are found nesting in crawl spaces and basements, but may be found in attics and ceiling areas if the population is large.

  • These rats range from 50-150 feet from their nests. Under duress these rats can travel up to 300 feet daily to obtain food and water.
  • The Norway rat’s nest may be built from a soft material such as paper or grass. If necessary, the Norway rat will climb a structure to enter a building. The Norway rat is also an excellent swimmer.
  • Expect most Norway rat activity during the night. Their peak times are either just before dawn or at dusk. If their population is large or if they are disturbed, you can detect activity during the day.

Control Options

Norway rats eat and contaminate food and damage properties by gnawing and burrowing. They spread diseases that affect people and pets.

Below is information on the many rat control options, such as rat repellent, traps, and rodenticides. We also offer prevention tips to help you with rat control, such as rodent proofing your home.

Eliminate Rats With Rat Traps

Rat traps are an effective method of non-toxic rat control. There are 3 types of rat traps commonly used for rodent control: Snap Traps, Glue Traps, and Electronic Traps.

These mechanical traps provide a quick solution to a rodent control problem and can be used many times. One advantage of rat traps is the ability to “recover” the rat to confirm its elimination.

The most important technique for effective trapping is good trap placement in areas of high rodent activity. The most common trapping mistake is using of too few traps.

Statistics show that more rodents are trapped on the first night than on any other night. For this reason, it is essential to use a large number of traps initially.

Some rats are harder to catch and are Neophobic or “extra cautious” of new objects that suddenly appear in their environment. For these cases, rat traps should be placed out, but left unset and baited for a couple days prior to setting the traps.

Eliminate and Prevent Rat Infestation With Repellents 

Ultrasonic rodent repellents are an effective method of controlling rats. These high-pitched frequency sound waves emit a non-repetitive pattern to prevent rodents from habituating to the sound.

For additional effectiveness, the loudest spike in sound replicates the scream of a dominant male rodent. Rodents are very territorial and will constantly fight to establish dominance. The sound of a dominant rodent will discourage others from inhabiting a territory.

It is important to note that ultrasonic frequencies do not travel between walls. So for the most effective rat control, ultrasonic units need to be placed in multiple rooms.

The most common repellent mistake is using them alone to control an established infestation.


Rodent populations will continue to increase in conditions that allow easy access to food and shelter.

Sanitation efforts in conjunction with rodent proofing provide the best solution to reduce or completely eliminate these conditions.

Two excellent tips are to seal off openings to your home and eliminate their likely food sources.

  • To adequately keep rats out of your home all openings need to be sealed off – remember rats only need an opening of 1/2″ or the size of a nickel to gain entry to your home.
  • In addition to exclusion, careful storage of foods and elimination of clutter are valuable steps in the fight to control rats. If Norway rats become established in or around your yard, they are usually obtaining food from obvious sources. These include garbage, outdoor dog pens, vegetable gardens, compost piles, and or bird feeders.

And remember, it only requires one poorly managed house or yard for a colony of rats to take over the neighborhood.

Related Articles:

Two Step Rat & Mice Control Process
Roof Rats: Facts & Control

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