Rats are small rodents and among them, Norway rats (Rattus norvegicus), or more commonly known as the street or sewer rat is one of the most common and widespread species of rat that there is. These creatures can be found in almost all continents besides Antarctica however, they are most common in North America and Europe. They seem to be almost everywhere that humans are, especially in urban areas where they find refuge in the sewers and streets. Norway rats are notorious for being a pest. They get into the property and leave it damaged, spread many diseases, and spoil food storages.

Male rats are commonly known as “Bucks” while females are known as “Does” and their children are known as “pups” or ‘’kittens’’. A group of rats is known as a “Mischief” of rats.

Why are they called ‘Norway rats?

Considering the fact that these rats are not originally from Norway, it seems unwise to name them after the country. But it was done so, and the true reason behind this inaccurate name is not really known.

Norway rats and scientific research

For many years, Norway rats have been used for research purposes. When we talk about studies done on rats, we usually are referring to this exact species. It is thought of as being the first mammal that was domesticated to research on. Basically, the rats, being mammals, social animals, having a quick lifespan, and having certain biology very close to human beings, are very close to an ideal sort of study subject for scientists. Hence they were domesticated for research. They were bred in a way to produce a model organism. This organism is what is being used by scientists now.

What do Norway rats look like?                                                   

 These rats usually have a coarse brown or grey fur which has black hair dispersed all around it. Their undersides are more or less always a lighter color such as grey to off-white or even yellow. Their eyes, as well as their head, are small while their tails are even shorter than their body. Adult Norway rats have a body of about 7-9 inches including their head while their tails are about 6-8inches. Their nose is blunt and they have small close-set ears that will not cover their eyes when they are pulled down. Their tails are usually scaly and don’t have much hair on them. 

Where do Norway rats live? 

Although Norway rats have ‘Norway’ in their name, they are not actually native to the country. They are in fact, natives to the northern regions of China. In the 18th century, they became more spread throughout the rest of the world because of the growth of international trade. In the present day, these rats are now found throughout the world except for Antarctica. 

In the past, Norway rats used to live in the forests. However, over time, since they were domesticated for research purposes, and bought into different areas, they have now become capable of making a home almost anywhere. They prefer to live in or near areas where humans are. They can live in not only forests, but sewers, buildings, and open fields as well. 

When making their homes in nature, Norway rats tend to live underground in burrows or tunnels. In the starting, their burrows are very short, usually about 20-25 inches. These burrows and tunnels may then grow larger and become interconnected. They eventually become a big complicated system with one entrance opening. The entrance opening is also the only path of exit onto the surface for escape. The tunnels may be used by many several distinct rat families, with the dominant rats active at night and the subordinates active during the day. Besides burrows, Norway rats also have nests and territories which can usually be found near sources of food such as barns or in yards as well. These rats tend not to stray farther than 50-150  feet from their nest. However, in extreme cases, they might be forced to travel longer distances, up to 300 feet, in search of food. 

What do Norway rats eat? 

While being able to eat most foods, Norway rats usually consume foods with a lot of protein and carbohydrates. They prefer high-quality foods such as meats, fruits, cereal grains, etc. Their diets are usually balanced. Norway rats also need water for survival which they get from ponds (if outside) or toilets (in buildings). They require about a half to a whole ounce of water each day. Rats that live outside may enter buildings to feed and then leave right after. Norway rats may also eat small mammals and insects as well and do not shy away from eating birds and other somewhat larger animals as well. 

What is their lifestyle?

Generally, Norway rats tend to live in large groups called packs. A pack is created when a male and female rat separately go and live somewhere and make their own nest. Their ‘societies’ tend to be hierarchical and male-dominated. They base their authority on size. Their young play-fight with each other. Generally, rats huddle together and learn from each other. They are capable of jumping, diving, and swimming as well. They like small, dark spaces and move on their four limbs. They have whiskers, each of which they can individually move. 

Norway rats tend to be territorial. They don’t like intruders in their territories and can be aggressive with them. Female Norway rats are protective of their babies and nests. They become aggressive during the postpartum period. Norway rats are also very curious minded creatures. They like to explore a new place.

These rats have a very keen sense of smell. They rely on their sense of smell to be able to identify each other as representatives of their own or some other pack. They can also tell each other’s sex, age, and even reproductive status using smell.

Norway rats like to be active from evening time onwards into the night. That being mentioned, they can also be awake during the day time. They are not too keen to run into humans and generally avoid them. As a pet, they might live up to 4 years but generally, in the wilderness, their average lifespan is closer to 2 years.  Most of their lifestyle revolves around eating and mating.

How do Norway rats reproduce? 

Norway rats mature at around 3 months old, at which point they are old enough to mate and bear children. They mate with many different partners, which means that they are polygynandrous. They can bear up to 6 litters a year. One Norway rat litter consists of usually 5-10 pups. Meaning that one pair of Norway rats can make up to at least 45 pups a year just by that one pair of rats, minus the ones that the new pairs make. The young pups are without fur and blind at birth. Their eyes open after about 9-14 days. Norway rats can reproduce any month of the year but reproduce more during spring and fall.

Are Norway rats aggressive? 

When in smaller numbers, Norway rats are territorial and aggressive as they have to force intruders out of the burrow. However, when a burrow grows and the number of rats increases, they become less hostile as they aren’t able to keep out every intruder as there would be too many intruders when the colony gets bigger and it would be harder to drive them out. It would be much easier to just give up and let them be. 

Do Norway rats bite? Can they hurt human beings?

Generally speaking, all rats tend to have pretty big teeth and thus are capable of biting. However, normal, healthy rats try to avoid people so there are fewer chances of being bitten by them. If they do bite though, it can be painful. There is often bleeding as well. Generally, a rat is not likely to bite you unless you directly threaten it in some way, or if it is crazy. I mean that literally. If a rat is carrying a disease it can display violent behaviors and bite people for no reason. The rat will bite an exposed, easily accessible part of the body, such as hands and feet. If they do bite you, don’t worry. It’s probably not serious. Usually, they just wash the bite, disinfect it and release the person who is bitten.  

Do rats carry rabies? Does the Norway rat carry rabies?

The answer is no. Rats and rodents are not known to carry rabies, although they can cause and carry several other diseases and parasites. Their tendency to go anywhere and live in sewers has made them undesirable and a health hazard. 

Norway rats as pets? 

It’s not uncommon for people to want to keep rats as pets. Norway rats happen to be just the same as other rats. They can make awesome pets, granted you get them young, and know how to work with them. Norway rats have smaller eyes and ears than other rats. Moreover, Norway rats are much shyer than other ones and are much more excitable than domestic rats. After getting them, you should make sure to check them for diseases before letting them run around your house. Make sure you also keep them away from other rats until the tests come in clear. Extreme care should be done when introducing wild Norway rats to other rats; make sure to do it very slowly and cautiously with plenty of room for the Norway rat to escape. This is so as Norway rats are much, much more sensitive to pheromones and have been known to die from shock if they are put in with other rats whose pheromones they don’t recognize or are not used to. 

How to prevent a Norway rat infestation. 

If you don’t live in Antarctica, then chances are a Norway rat might stop by your place of residence and decide to start a family there. While this does seem like a scary thought, you’ll be happy to know that there are some ways we can use to convince the rat otherwise. Norway rats have a moth-like attraction to wood, so you should be sure to keep your firewood stored in a place where they can’t reach it as well as removing any random debris piles. This is so as they make perfect nesting spots for Norway rats. Norway rats in search of drinking water will probably settle near a water source such as leaky pipes, so its best to get those fixed too. It is also important to note that you should use steel to fix any holes in the house so that they don’t get in and line all doors with at least 5inches(in length) of steel at the button so that they can’t chew their way through. Make sure that all your food products are properly sealed at all times as Norway rats are notorious for spreading dangerous diseases. In the same manner, make sure that your trash bags are properly enclosed in the trashcan and that the trash cans are cleaned often. This is so that Norway rats do not find them as a food source and settle in near or inside your residence. 


How to know if you have a Norway rat infestation? 

It might be a bit hard to find rats during the day as they are nocturnal animals, meaning they are usually active at night. But there are still some sure-fire ways to check if your house or property has rats or not. 

First comes, gnawing holes. These holes are made when a rat gnaws or bites and chews on an object and is about 2 inches or more in diameter. One of the most common things rats love to do is gnaw or chew on stuff.  Everything, from personal belongings to woodwork and electrical wiring, what a rat can chew will chew. Their gnaw marks are roughly 2inches in diameter.

 Then comes tracks. A normal mouse track will be much shorter than that of a roof rat or a Norway rat. The tracks that Norway rats make are made of their hindfoot and are usually about 3⁄4-1 inches and will also have a mark between their feet tracks as rats tend to drag their tails. Another way of knowing whether or not there is a Norway rat in your home or place of residence is to look for their droppings. Rat droppings are thrice the size of mouse droppings. Norway rat droppings are usually 1⁄4 to 1⁄2 inches in length and are capsule-shaped with blunt ends. The droppings are black and usually have a shine to it but that may vary from the diet. Another way to check is to check your food products in place that you think a rat can easily get to. If they look as if they have been rummaged through, then they most probably have been, Of Course, this doesn’t specifically mean that you have rats in your house, but just in case, you should throw them out and buy new ones, placing them in a place where rodents can’t reach. 

Burrows are also a sure-fire way to check for Norway rat infestations. Norway rats tend to make burrows near walls and food sources, so check for any holes in your walls or other parts of your house. Most of all, be vigilant.

How to get rid of a Norway rat infestation?

There are several ways you can try and get rid of these pesky creatures. 

The most important thing is to try and make sure they are not able to fulfill their basic needs from your home. This means making sure they don’t have access to any water, food ++or shelter. 

Do this by making sure your garbage cans are covered completely in such a way that rats can’t sneak into them for food. Make sure you clean up after eating and store your food in a sealed container. If you have any pets, store their pet food in sealed containers as well.  Empty them out often. Fix any plumbing related issues, especially water leaks, to seal up all sources of water for the rats.  Clean up regularly and make sure to get rid of any remnants of pet feces/droppings. 

To prevent rats from finding shelter of any sort, get rid of piles of debris in your house or yard. If there is firewood in storage, make sure it is kept away from structures. Check around your house and if there are any tree limbs that are touching the house, cut them off. 

Another important thing you need to do is to seal all crevices. These rats are tiny and can get in through holes and cracks. Seal them up in areas such as around doors, chimneys, windows, and dryer vents. Cover dryer vents with a screen.  Close your doors, especially at night when the rats are active. 

At the end of the day, if you notice that the rat problem is not going away, you might have to call in professionals. 

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Dusty Showers has been in the urban nuisance wildlife and pest control field since 1993. Taught by Garon Fyffe, a pioneer in humane nuisance wildlife management, Dusty has a passion for finding humane solutions to human & wildlife conflicts. Dusty was the only individual invited by the Florida Fish & Wildlife Commission in the lat 1990's to help write legislation for legal protection of Florida bats. With an instinct for solving wildlife, Dusty found pest control to be an easy "add-on interest". Dusty started his first business "Animal Instincts Wildlife & Pest Management" in the Tampa Bay, Florida area in 1995. Eventually selling Animal Instincts in 2002, Dusty went on to start Creepy Creatures Termite and Pest Control in 2009, which he still owns and operates today in Palm Harbor, Florida.

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