Mice vs rats – what are the differences between these pests?

Do you think you have a rat or a mouse problem? Is one of these pests more concerning than the other? Learn about the main differences between rats and mice so you can better identify which one is causing problems in your home. We’ll start by answering some of the most commonly asked questions about these rodents.

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

Mice and rats: are they the same?

Mice and rats are both commensal rodents and belong to the mammalian order Rodentia, but that doesn’t mean they are the same. In fact, they are not the same because mice belong to the Mus genus and rats belong to the Rattus genus.

Do mice turn into rats?

No, because they are separate species and do not interbreed. Mice, therefore, are not baby rats and neither do they grow into rats.

What are the key differences between rats and mice?

While some similarities between them can make it hard to tell the two apart, there are some differences between mice and rats that will hopefully help you identify which one you’ve seen.

For example, while rats tend to have longer tails than mice, they also tend to be larger than mice. But, it can be hard to tell a baby rat from an adult mouse. This is just one difference between these two, so let’s look at how else they differ.

House mouseNoway ratBlack rat
Size and weightThe size of the house mouse varies depending on where it lives and the availability of food.
Most house mice are about 5 to 8 inches (13 to 20 cm) in length from nose to tail.

The average weight of an adult mouse is 0.5 to 1.0 ounce (14 to 28 grams). Some can be larger and reach lengths of 25 centimeters and weights of 40 grams.
Rats are significantly larger than mice, especially the Norway rat. An adult is around 16 inches (41 cm) in length, including the tail.
The Norway rat’s tail is shorter than its body.
They weigh an average of 12 ounces (340 g), so you can see how much bigger they are compared to the house mouse.
The black rat is slightly smaller than the Norway rat but bigger than a mouse.
The black rat grows to 6-8 inches (16-20 cm) and weighs 8-12 oz (226-340 g).
ColorAdults range in color from light brown to dark gray, but most often the majority of their body is medium brown, with the belly being a lighter shade of their general color or even cream colored.As the Norway rat is also known as the brown rat, its fur is as expected, brown with specks of black and a lighter-colored belly and feet.Dark gray to black colored fur with a lighter belly.
FeaturesTheir eyes are relatively small, but their ears are fairly large for the size of their bodies.
Their thin tails are almost hairless and roughly the same length as their bodies and heads combined.
Mice have longer and pointier noses than rats.
The body of a house mouse is slender, whereas rats are stocky and heavier.
A rat’s nose is shorter and blunter than a mouse’s.
The tail is thick, fur-less, and scaly. The ears are small and covered in short hairs.
The nose is shorter and blunter than a mouse’s.
The tail is thick, fur-less, and scaly.
The ears are larger than a Norway rat’s and almost hairless.
Difference between rats and house mice

Differences in mice and rat droppings

Although mice and rats share several similar traits, it can still be difficult to know which one is infesting your home, especially if you haven’t actually seen one but you are finding droppings.

How else do you tell if it’s rats or mice? You can get a good idea of which one it is by the fecal pellets. Not only will you know what is infesting your home, but you will also find out where they are and the size of the infestation.

An infestation is easily identified by droppings, and a pest control technician looks for these to confirm whether it’s a mouse or rat infestation, or if it’s another pest altogether, such as American or Oriental cockroaches, as these roach droppings are often mistaken for rat or mouse feces.

  • The droppings from the house mouse are tiny. They are rod-shaped and 0.25 inches (0.3-0.6 cm) in length, and usually have one or both pointed ends. A single mouse produces around 60 pellets a day.
  • Deer mice and white-footed mice produce fecal pellets that look almost the same as those of house mice.
  • Rat droppings are larger, especially those of the Norway rat, whose droppings have blunted ends, so they kind of look like capsules and are around 0.75-1 inch (2.5-2 cm) in length.
  • About 50 pellets are produced daily by this rat, which are usually found clustered together in corners and behind objects.
  • The droppings from the black rat are slightly smaller at 0.5 inches (1 cm) in length, and they are spindle-shaped and more curved than the Norway rat’s droppings. They are usually more scattered instead of being found together.
  • The color of their feces varies between shades of brown and black. But this also depends on what food they feed on in your home.
  • Mice and rat poop can also contain hair, which is ingested when grooming themselves.
  • In contrast, old droppings are hard and crumbly, while fresh poop glistens and is more pliable. The size and amount of fresh feces give you some indication of the size and severity of the infestation.

If there are lots of fresh pellets of different sizes, then both babies and adults are present, which tells you an active breeding population is present and will become a significant pest issue.

Droppings will be found in areas with a lot of activity, so set traps or bait stations there. Primary areas include runways, corners, food sources, and harborages.

How to tell a rat from a mouse by the gnawing marks

Another way to identify the rodent is by the size of the grooves left by chewing and gnawing. Both pests target baseboards, wires, wood, and everything in between, but mice leave tooth marks of only 1–2 mm wide, whereas rats leave marks of 3.5–4 mm wide.

Can you have a rat and mouse infestation in your home at the same time?

The term “muricide” describes how rats have a predatory instinct to kill mice. Rats will not tolerate mice in the same areas as them and will eat (or partially eat) the mice. Having competition for food is not in the rat’s nature.

I have never seen both a mouse infestation and a rat infestation inside a building at the same time. However, I have seen evidence that both have infested a building, but at different times.

This is not uncommon, as mouse infestations are often seen after rats have left or been eliminated. Mice use their sense of smell to detect the freshness and decay of the pheromones left by rats; if the pheromones are old and the mice don’t see any rats while inspecting the outside areas, then they will move in.

However, there are instances where they coexist, but that is only when there are unlimited food supplies and ample harborages. This is more likely to occur in a food production type area than in your average house.

If you happen to live where you get both Norway rats and black rats, then you can find both of them in a building, but they tend to stay in separate areas. The black rat is also called the roof rat, so it likes the upper areas of your home, such as the attic, while Norway rats prefer to burrow in the ground outside or stay on the ground level of your home.

Is a rat infestation worse than a mouse infestation?

Let’s be clear, you really don’t want either of these pests in your home. They are both destructive and can cause significant damage.

Both have a constant need to gnaw, and they will gnaw your furniture, baseboards, food, drywall, insulation, and worst of all, electrical wires. Rats and mice can be a fire hazard!

Rats have stronger teeth than mice, so they can chew their way through the hardest of surfaces and materials.

Mice, on the other hand, are prolific breeders, so your home can be overrun with baby mice within days. These little critters can easily hide anywhere as they can fit through a gap or crack that is only 5-7 mm wide. That’s about the width of a pencil![1]

Are mice or rats harder to get rid of?

Generally, rats are harder to get rid of because they are neophobic, which means they are suspicious of anything new they find in their surroundings.[2] It takes them a long time to investigate a newly placed bait station or trap, so it can take a lot longer to get rid of them.

Mice, on the other hand, are much more likely to approach something new right away, such as a trap or bait, making them somewhat (sometimes) easier to control.

Do mice carry the same diseases as rats?

Salmonella and Campylobacter, which cause salmonellosis and campylobacteriosis, respectively, are just two of the harmful bacteria that cause food-borne illnesses spread through food and water contaminated with rat or mouse feces.

And if that’s not bad enough, the fecal pellets and urine of either of these pests contain proteins that can trigger asthma and allergies if you are prone to them.

Diseases, such as plague can also be transmitted to us and our animals by the ticks, mites, and fleas that they carry. According to the World Health Organisation, “plague is transmitted between animals and humans by the bite of infected fleas, direct contact with infected tissues, and inhalation of infected respiratory droplets.”[3]

Rats and mice are public health pests, so it’s vital to get rid of them as soon as you notice any activity.

Mice and rats

Now that you know the differences between mice and rats in terms of how to identify them, you also know just how harmful it is to have either one of them in your home.

If you suspect you have one of these rodents, there are steps you can take, such as placing traps and bait stations in the areas you’ve identified as having high activity. Alternatively, and this is the best option, especially if you aren’t comfortable using these types of traps, is to hire a professional pest control company to do the job for you.

However, before you call in an exterminator, read my page about how to choose the right pest control company, so you know what to look for and what questions to ask about the company.

1. https://www.pctonline.com

2. https://www.ncbi.nlm.nih.gov

3. https://www.who.int