Overview of the Norway Rat

The Norway rat is one of the two most common rats in the United States. The second is the tree rat. Also known as the brown rat or sewer rat, the Norway rat is a common invader of homes, businesses, and other structures. We present an overview of different aspects of the biology and life of the Norway rat.

Physical Description of the Norway Rat

A Norway rat has coarse fur. Typically, the fur of a Norway rat is brown but there are rats of the species that have dark gray fur. The stomach area of a Norway rat usually has a lighter shade of brown or gray.

An adult Norway rat can grow to between 6 to 11 inches. An adult weighs between 6 to 18 ounces. When contrasted with the tree rat, a Norway rat commonly is about twice the size of a tree rat.

The Norway rat has a powerful sense of smell. In addition, this species of rat has acute hearing. This species of rodent can hear ultrasound. A typical Norway rat has poor vision at about 20/600. The situation is even worse for an albino or non-pigmented Norway rat, which has a vision of 20/1200.

Reproduction and the Norway Rat

Provided conditions are suitable, Norway rats breed throughout the year. What this means is that provided that they are able to reside in a warm, sheltered environment, they will reproduce throughout the year.

The Norway rat reaches sexual maturity at about five weeks. The gestation period for a female rat is 21 days. Interestingly, if food is restricted for one reason or another, a female Norway rat has the ability to extend pregnancy by over 2 additional weeks.

The typical litter averages 7 pups. (Infant rats are known as pups.) Litters of up to 14 are possible. A female can produce up to 5 litters annually. Rat populations can increase so rapidly that in theory a male and female can expand from that population of two upwards to 15,000 in 12 months. Indeed, if a rat colony sustains a mass extermination, the remaining rats will up their reproductive pace and rapidly restore the prior population level.

Life Cycle and Social Structure of a Norway Rat

As mentioned, a Norway rat reaches sexual maturity at just over a month. A Norway rat can live up to three years. With that said, due to predators and conflict that can exist within a colony, most Norway rats do not make it to a year.

Norway rats live in large and hierarchical colonies. They live in burrows or in other locations like basements or sewers. If food becomes in short supply, the rats lower in the established hierarchy are the first to die.

Living in colonies, Norway rats sleep together and groom one another. Colony members will act aggressively towards an outside rat. Generally a nocturnal animal, Norway rats are most active beginning in the evening until the dawn.

Diet of a Norway Rat

Norway rats are omnivores. The reality is that a Norway rat will eat almost anything it can get ahold of, depending on where the rodent lives. With that said, Norway rats that infest homes are thought to be most fond of cereal.

Norway Rats and Disease

As is the case with many rodents, Norway rats do carry dangerous pathogens that can result in illness in humans, including serious and even potentially fatal disease. These include:

A common misperception is that this type of rat is responsible for spreading the plague. While it is possible for the Norway rat to bear the fleas that can infect humans with the plague, this type of rat rarely is such a carrier.

Eliminating a Norway Rat Infestation

Because of the potential destructive behavior of Norway rats, coupled with possible health risks, if an infestation occurs in your home or business, it is imperative to take prompt action to eliminate the colony. In most cases, this objective can be effectively accomplished by engaging the services of a professional rodent eradicator.

Bear in mind that eliminating the rats themselves is only part of the problem. You also need to thoroughly clean up any rat droppings that remain in the aftermath of an infestation.

Rat droppings can harbor serious disease, including hantavirus. This type of virus can remain alive and viable in Norway rat droppings for an extended period of time, even after they dry out. Dried Norway rat droppings become particularly dangerous because they crumble easily. When they crumble, dust containing the virus or other pathogens can become airborne. If a person inhales the dust containing the virus, that individual can become infected by the hantavirus.

Based on the serious health risks that Norway rat droppings can present, if you find yourself in this situation, you need to seriously consider engaging the services of a rodent dropping cleaning professional.