What Are Brown Rats? 

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There are many different species of rats; roof rats, woodrats, and marsh rats are among the pests you may encounter in your home or property. The rat you are most likely to see is the brown rat, which goes by the scientific name rattus norvegicus. 

So what are brown rats? Brown rats are also called Norway rat, common rat, sewer rat, or street rat. These rats are believed to have arrived in the United States on ships that came from Asia during the 1700s. Although they have poor vision, brown rats are agile and have strong senses. They are known to spread diseases and cause damage to structures by gnawing.

The History of Brown Rats

Brown rats boast a long history with humans. They are native to Central Asia and Northern China where they thrived in forests and bushy areas. The species found its way to Eastern Europe and North America as stowaways on ships in the 18th century.

It’s not clear why the brown rat is also called a Norway rat when this species didn’t originate from Norway. One theory is that English naturalist John Berkenhout caused this misnomer as he mistakenly believed the brown rat to have migrated to England from a Norwegian ship, a mistake he popularized in his 1769 book on the natural history of Great Britain.

Brown rats are agile and adaptable which is how they have survived for so long. Brown rat populations can be traced to every continent except Antarctica. It can be said they have been following humans around. From the green forests where they originated, brown rats now prefer to live in urban areas where there are more food sources.

How to Identify a Brown Rat

Brown rats are given this name for their brown-grey coloring. Their fur is coarse and bristly, usually with a bit of black hairs mixed in. Their undersides are lighter in color and may look greyish, off-white, or even yellow at times. When they are bred as pets, Norway rats could also be pure white, black, or brown.

The brown rats’ short fur covers their entire bodies except for their nose, tail, and ears. Their ears are covered in hair while their tails are covered in scales, which helps them balance. They also have a blunt, squarish muzzle.

Norway rats can grow to be quite large, the males especially. On average, they can reach 16 inches or 40 centimeters in length. This includes their tails which are shorter than the rest of their body. In terms of weight, some brown rats can weigh over half a kilogram; their large bodies tend to make their eyes and ears look much smaller in appearance.

Brown Rat Habitats

Brown rats can survive in any place that can provide them food, water, and shelter. As they are omnivorous and can eat anything, they have a wide range of habitat options.

While Norway rats are typically associated with farms and can live in burrows near hedgerows or cereal crops, they have also become more common in towns and cities, especially port areas. In human homes, they are capable of making nests in roofs, wall cavities, and under floorboards. They may also prefer to live in outdoor sheds and gardens.

As they are called sewer rats, you may also find these brown rats residing in sewer systems. From there, they can infiltrate homes and properties through pipes and other entrances.

Brown Rats: Characteristics, Diet, and Behavior

Brown rats are incredibly intelligent animals, which is how they adapted to live alongside humans for thousands of years. With the combination of their characteristics, diet, and behavior, rats can outsmart and outlast many pests in human households.


As they are colorblind, nocturnal creatures with poor eyesight, brown rats rely on their strong sense of hearing, smell, taste, and touch when they actively look for food and water at night. They spend their days sleeping and eating although some rats may be more active in the mornings when the rat population is high.

Brown rats have exceptional senses that guide them in avoiding most predators and threats. They use ultrasound, posturing, and gestures to communicate with one another while their sense of smell helps them recognize other rats. They can also easily locate food and detect any contaminants with their sense of smell and taste, which is why trying to bait them can be difficult.


Norway rats will eat almost anything humans do and more. In agricultural areas, they tend to eat cereals, grains, root crops, and livestock feed. For brown rats in urban areas, household garbage cans provide them a balanced diet of meat, fish, bones, and fruits. They may also eat dog food or bird feed scraps.

If food is scarce, brown rats will also kill and eat small insects, reptiles, mammals, and even birds. Unlike mice, rats need to drink water daily. When they feed on purely dry foods, these rodents will have to drink 0.5 to 1 ounce of water a day. They will look for nearby sources of water and can drink from toilets, sinks, rain puddles, and condensing water from utility pipes or air conditioning units.


In the wild, brown rats can survive for up to two years with their skills in swimming, diving, and climbing. As they grow, their incisor teeth do as well which is why they will gnaw on everything except steel: wood, plastic, lead, bricks, insulation around electrical cables, and so on.

Brown rats also reproduce quickly. An average female rat will bear 4-6 litters a year; each litter may have 6-12 offspring born three weeks after conception. After three months, these offspring rats are adults who can reproduce as well. Their breeding period is not seasonal but increases in warmer months.

Because brown rats live in such large families, they have to dig extensive burrows that can support their population. As social pests, brown rats tend to live in large colonies and build interconnected burrows. This underground network can be used by generations and each shelter is filled with shredded paper, cloth, and fibrous materials for comfort.

Brown rats also participate in social hierarchies that they determine by size. The largest male rats belong at the top of the pyramid and live in burrows closest to the food source. Lower-order rats have less access to food and they are the ones you can see scavenging in the daytime. When food supply is low, these weaker rats are the first to die.

The only reasons a brown rat would enter a human residence or property is when food and water become scarce during colder months. They can squeeze into any entrance the size of a quarter so it’s easy for them to find a nesting area on human property. Rodents will look for shelter in basements, sewers, attics, roofs, and lower floors of a building. They tend to nest in piles of undisturbed materials and debris.

Are Brown Rats Dangerous?

If brown rats have invaded your residence or business space, you must deal with them immediately. They can be very destructive and dangerous towards structures and people, especially younger children. These rodents are also well-known carriers of various diseases. Here are some of the dangers a brown rat infestation may pose:

Health Concerns

Brown rats are carriers of certain pathogens and bacteria. Through their urine, saliva, or droppings, they can transmit diseases. Humans can also be infected with these diseases if they get bitten or scratched by a rodent. You may also get sick if a rat contaminates your food or passes through counter-tops in your kitchen where food is prepared later on without disinfecting. Some rat-borne diseases include:

  • Leptospirosis
  • Salmonella
  • Listeria
  • Toxoplasmosis
  • Rat bite fever
  • Viral hemorrhagic fever
  • Q fever (or query fever)
  • Hantavirus pulmonary syndrome (HPS)
  • Lymphocytic choriomeningitis (LCMV)

Damage to Property

Brown rats can cause a large amount of structural damage on your home or commercial property. Because they can chew through anything, they can destroy your walls, floorboards, and furniture. You may even see teeth marks on objects these rodents have gnawed on.

In many cases, brown rats use their teeth to create entrances in the foundation or walls of your home. They also carve out nests from themselves beneath building foundations and inside walls, ceilings, or cabinets.

Among the most dangerous things a rodent can do to your property is to puncture water pipes, chew through gas pipes, and chomp away at the insulation around electrical cables. In this way, they can cause floods, gas leaks, and serious fires.

Harm to Children

While it’s rare for wild brown rats to bite humans, it still happens. The exact number of yearly cases is difficult to determine as these bites are underreported. Urban brown rats also tend to bite people at night when they are asleep, on parts of the body that are exposed such as the hands and fingers.

Although people of all ages can be rat-bite patients, a majority of victims tend to be young children. One theory for this phenomenon is that brown rats are attracted to the smell of milk that lingers on children’s skin. Fortunately, rat bites are usually not severe and the infection rate is very low. However, rare cases have shown that rats can transmit a disease called “ratpox” or rat bite fever through one bite, which parents should be cautious of.

Preventing a Brown Rat Infestation

Like any other wild animal, brown rats enter human residences and commercial reasons seeking food, water, and warm shelter. They don’t intend to cause harm but their natural instincts drive them to do destructive things as they try to access resources inside your home.

It is better in the long-run to prevent brown rats from invading and breeding inside a building because they can cause a lot of costly damages. There are several measures you can take to make sure these rodents don’t take up permanent residence with you.

  1. Eliminate all entry points by sealing gaps and repairing any openings. Rats can easily pass through a 15 mm. entrance to get inside a building so it’s important to close off any cracks and crevices. A quick solution would be to stuff steel wool because rats cannot gnaw through steel.
  2. Anything that is edible should be properly sealed and stored in tight containers. Garbage cans and compost bins are particularly attractive to hungry brown rats looking for food scraps. It’s also important to empty trash cans regularly and clean up after your pets’ food bowls so rodents won’t be attracted to the leftovers in your home.
  3. Avoid feeding garden birds excessively. Rats and mice alike can climb up bird feeding stations to eat bird food. Be sure to sweep up any bird seeds that are scattered around your property as well. A good alternative is to buy a squirrel-proof feeder instead to keep other animals from getting to the bird food.
  4. Move stuff around. Rodents are neophobic. They have a fear of new things and situations so keep them on their toes by rearranging your furniture frequently. Rats don’t like it when the landscape gets disturbed and they will be warned off from getting too comfortable. You can even position furniture around as obstacles that keep them from coming inside.
  5. Keep pets around. Rats are more sensitive when they smell dogs and cats so they won’t linger around your property. Of course, pets are just a deterrent. It’s not advisable to keep a pet to catch rats as the rats could still transmit disease to other creatures.
  6. Remove any water sources and close all taps. Rats are always on the hunt for a steady supply of water. If your property doesn’t have a source, they will move elsewhere. Keep your drains secure, eliminate sources of moisture, and add baffles to your drain pipes for good measure.
  7. Get rid of all potential nesting sites. Rats love cluttered areas that few people visit so it helps to keep your attics and basements tidy. You should also take care to clean up your lawn and garden. Rats can nest in overgrown places, piles of wood or leaf debris, and even shrubs. When your garden plants are cut short and your lawn is free of rubbish, rodents will think twice to take over your space.
  8. Ask your neighbors if they are experiencing any rat issues. Because brown rats are social creatures, they tend to spread in neighborhoods. If your local community has observed increased rat activity, each household should clean up and prepare against a potential infestation.
  9. Call a professional exterminator or pest control. Professional rodent control experts can plan preventative measures for your property, identify entry points, and set up traps or bait stations to keep your building free of rats.

Signs You May Already Have a Rodent Infestation

Brown rats and other rodents prefer to stay away from humans as much as they can. They are secretive and suspicious so unless you have a large population of rats living in your home, it’s unlikely you will see one in the open. Some telltale signs of a rodent infestation include:

  • Droppings: Norway rats excrete up to 40 dark, capsule-shaped dropping every day. These droppings are usually found near entry points or passages the rats frequent. Rat droppings look dark and shiny when fresh but grey and dusty when dried up.
  • Urine smell: Rat urine emits a powerful, musty smell. Like any other animal, their urine is composed of urea and water. Once the urea breaks down, nitrogen is released and creates ammonia -- the source of the strong smell. When rat urine is dry, it will also have crystallized, chalky bits of calcium in it.
  • Footprints: Many rats leave foot and tail marks in dusty areas. To check if there is an active rat infestation, sprinkle fine flour or talc powder on the floor and see if any fresh tracks appear the next day.
  • Grease marks: Brown rats are creatures of habits. With their poor eyesight, they tend to follow established routes along walls and surfaces. When they pass by these routes, they brush by and leave grease stains. If the stains are dark, this indicates greater activity as the rats pass by frequently.
  • Bite marks and holes: Check the holes around the wooden areas of your building. If the hole is smooth, it tends to be older from wear. However, rough new bite marks could indicate rodents chomping on the wood. Damaged food products and packets with gnaw marks should also alert you of a rat’s presence.
  • Nesting materials: Piles of shredded papers, leaves, cloths, and other materials may indicate a nearby rat burrow. If you see these nesting materials lying around or bitten through, keep track of the area and monitor to see other signs of rodent activity.
  • Sights and sounds: When an infestation is severe, it becomes more obvious to homeowners and residents through rat sightings and sounds. At night, you may hear scurrying noises when they move through walls or pipes around the building. You might also spot their burrows around the building, hidden under dirt mounds and leaves.

Let Pinnacle Pest Control Handle Your Rat Infestation

Rodent control is most effective when you have experts handling the mice and rats on your property. Pinnacle Pest Control has been helping Sacramento residents and business owners manage pests since 1998.

For over 20 years, our team has implemented rodent control procedures and preventative measures for hundreds of satisfied clients. Since we began, Pinnacle Pest Control has grown into a highly-trusted rodent control service provider in Northern California. To learn more about our services, schedule an inspection with us today.

Learn more: What Rodent Has the Longest Lifespan?

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