Rats: What You Should Know About This Pest

Written by: A O’Neill, Licensed Pest Management Professional

What are rats?

Rats belong to the mammalian order Rodentia. They are one of the most prevalent rodents in and near our homes and are social creatures. There are many different species of rat in the world today.

There are two common pest species of rats that we need to watch out for that can cause problems in the home; these are the Norway rat (brown rat) and the roof rat (also called the black rat).

As well as rats, the house mouse, and Deer mouse are the other types of rodents that can make their way into where we live.

So here’s what you need to know about rats, what attracts them to your home, and why you don’t want an invasion from this pest.


Rats are vermin

The common rodents that cause us concern are commensal and are called domestic rodents because they live in close association with people. And that’s because we supply them with their three basic needs: food, shelter, and water.

However, each of these rodents has its own set of habits and preferences, but all can harm our health.

Did you know? Approximately 21 million homes in the United States are invaded by rodents each winter. These pests can carry disease, cause property damage, and pose a serious threat to your family’s health and safety. Taking steps to prevent and control rodent infestations is essential to protecting your home and your family.[1]

Rats have been responsible for so much human suffering from plague epidemics like ‘The Black Death‘ and rat bite fever, to serious economic damage including feeding on stored grains and gnawing through electric cables, and causing fires.

You might be surprised to know that at least 20 percent of the planet’s food gets eaten or contaminated by rodents each and every year.[2]

Why do rats like our homes?

Rats like our homes because they provide them shelter from the elements and somewhere they can nest and reproduce. But most importantly, they find food easily in our homes, which is their big attractant.

Food sources include anything, and just like other public health pests such as cockroaches, this rodent is also not fussy about what it eats.

Norway rat taken a slice of apple to eat
Norway rat. Image: Ed Freytag, City of New Orleans, Bugwood.org

Where can you find rats living?

Where do rats not live? That would be an easier question to answer. Rats live in packs and inhabit various places, including granaries, sewers, basements, attics, barns, gardens, compost heaps, ships, skyscraper buildings, warehouses, shops, and subway tunnels.

They have adapted to living alongside us so well that you might not even know they are there until their numbers become so large, or you see one scurrying out in front of you.

Are rats a problem in big cities?

They definitely are a problem, and their numbers just keep growing. Cities offer them everything they need without having to travel too far to get it.

It was reported that London in the UK had 19,846,504 rats for the 2020/21 period – a 25% increase from the year before.[2]

New York City reportedly had around 2 million rats in 2020.[3]

While Canada has no official numbers, Vancouver and Toronto also report growing rat problems.

Quick rat facts

  • Rats can leap 3 ft (0.9 m) high and 4 ft horizontally.
  • They can squeeze through pipes that are only 1.5 inches in diameter.
  • They can get from one building to the next by walking along power lines and telephone lines.
  • Norway rats are also known as water and sewer rats as they can swim at 0.86 miles per hour (1.4 km/hr) and tread water for up to 3 days.
  • Norway rats are known as sewer rats for a reason, and it’s because they can swim through the sewer pipe and into your toilet, and if the lid is up, then into your home.
  • Rats gnaw continuously! The word rodent comes from the French word rodere, meaning “to gnaw”, and they have to because their incisors grow continuously and up to 0.4 mm a day.
  • Each type of commensal rat differs in size and color, making it hard to identify them correctly just by color alone.
  • A female rat can breed every month as long as she has access to food, water, and shelter.
  • Rats are neophobic, which means they fear new places and things, which explains why they may avoid new traps and bait stations. 

What do rats eat?

Rats are omnivorous, which means they will eat anything they come across, whether that’s plant or animal matter. To give you some idea, their diet includes garbage, food scraps, grass, leaves, insects, small animals, plants, vegetables, fruits, grains, meat, eggs, milk, fish, fungi, honey, and even animal and human feces.

When are rats most active?

As rats are mostly nocturnal, they’re most active during the hour following sunset and just before sunrise when they forage for food and mate. This is why they can be running around your home or business and you don’t know they are there at first.

However, these intelligent rodents are known to change their activity periods from night to day depending on levels of competition from other rat colonies, food and water availability, and our own activity.

Do rats have nests?

Like most pests that invade our home, they are all looking for the same things which are shelter, warmth, food, and water, and rats are no exception.

Rats are more likely to find a way into your home during the colder months of the year when they want to stay warm. They also look for dark secluded areas where they can give birth and rear their young.

Outside in your yard, rats will burrow down into the dirt and create a series of nest chambers between 5 – 8 inches (15 to 20 cm) in diameter. The entrance to these chambers is only around 1.5 inches (2 cm) in diameter, but that’s enough for a rat to squeeze through.

Inside your home, rats will nest inside the walls, in the basement, the attic, underneath equipment, in crawl spaces, and anywhere that is cluttered and secluded. Norway rats are usually found nesting on the lower floors but can be found on higher levels also, and roof rats tend to nest on the upper floors and attics, hence the name.

In the nests, you might find all sorts of items and foods taken from your home as pest rodents can be hoarders. I once found a load of potatoes in a rat’s nest!

What do rats use to build a nest?

Rats build nests out of almost anything. From leaves to sticks, paper to plastic, and from wood to wire. The most common nesting materials include wood shavings, paper products, leaves, grasses, straws, twigs, hair, feathers, clothing material, and fur.

The rat will layer the materials so the nest is not only insulated but also free of moisture.

Rats can cause significant property damage

Rats can cause serious damage to your home. Using their powerful front incisors they chew a whole load of materials, including:

  • Electrical wires in buildings and vehicles
  • Pipes
  • Insulation
  • Walls and ceilings
  • Floors and baseboards
  • Furniture
  • cabinets and countertops
  • Sheetrock
  • Soft metals such as copper and lead.

Gnawing damage can lead to water leaks, mold growth, structural problems, and even house fires.

Dealing with any kind of rodent in your home should be a top priority due to the sheer damage they can cause.

Can rodents make us sick?

As well as being common pests in homes and offices, causing damage to property and food supplies, they can, directly and indirectly, transmit various types of bacteria and viruses.

Direct transmission means contaminating food with their feces or urine. Indirectly, for example, could be when a flea bites an infected rat and then goes on to bite a person.

Here are just a few diseases carried by rats/mice:

  • Leptospirosis
  • Weil’s Disease
  • Plague
  • Salmonellosis
  • Rat bite fever
  • Hantavirus
  • Trichinellosis

Now you know that any rat or mouse is not something you want to find in your home, so how do you prevent them from getting in so you don’t have to worry about them spreading any nasty germs around your home?

Related: Mice vs Rats – what are the differences between these pests?

Keeping rodents out

Gaps in exterior of property where rats and mice could enter
Gaps on exterior of property give rats/mice easy access. Image: Liz Kasameyer, Johns Hopkins School of Public Health, Bugwood.org

The best and most important way to prevent rats from invading your home is to make sure you eliminate their food and water supplies. If there’s a supply of food that they can consistently get hold of, then the rat is there to stay!

Keeping all food, and that includes pet food and food in the pantry and cupboards sealed in glass or metal containers is the way to go. This limits their feeding opportunities as well as keeping everything clean and uncontaminated.

Use a covered trash can to keep things tidy, and be sure to pick up any clutter that might attract pests.

Make sure pet food isn’t left out overnight and water bowls are emptied.

Inside the home, make sure there are no holes or gaps in the baseboards or other places where rats can get in. Seal cracks under sinks and toilets, repair holes in walls, and remove clutter.

Keep your home clean and sanitized and wipe down surfaces frequently with disinfectants.

Make sure there’s a cap on the soil pipe so if a rat climbs up it, it can’t climb out and get into the attic.

If you see rat droppings, see if you can follow them back to where they might be entering your home so you can seal off any potential entry points.

Take a walk around the outside of your home and seal any gaps along foundation walls and basement floors with mesh and then caulk. It’s no good just sealing a gap with caulk as they can chew through it in no time.

Remove any food sources that might attract these rodents, such as garbage, pet food, and bird seed.

Seal gaps under and around doors, windows, and vents.

Repair loose siding and replace rotten wood.

Make sure to keep any shrubbery, woodpiles, and compost heaps at least a few feet away from your home, as these can serve as hiding places for rats.

Keep garbage cans tightly covered because rats have an amazing sense of smell and will find their way in if the bin is not covered properly.

If you notice any signs of rats around your home, then take action immediately. You could try using traps or bait stations depending on how humanely you want them treated.

Use caution when handling dead rats. Wear gloves and protective clothing when disposing of carcasses. Of course, the best way to deal with a rodent infestation is to let a professional exterminator take care of it for you as they know what methods work best.

[1] https://outofsight.pestworld.org/needtoknow/

[2] https://www.in.gov/

3] https://www.pest.co.uk/how-many-rats-in-london/

[4] https://www.nature.com/articles/d41586-020-00501-x