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What is the Difference Between Rats and Mice?

Tricia Christensen
Updated May 21, 2024
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Rats and mice have many differences and similarities. It is challenging to determine specific areas of difference and commonality since there are a number of types of both animals. Usually the two species are compared by evaluating the differences between house mice (Mus musculus) and Norway or black rats (Rattus norvegicus and Rattus rattus). These may also be called pet rats or mice or domesticated versions of each species.

Mice and rats cannot interbreed though they are related. Evolutionary biologists believe the two species share an ancestor, much in the same way that tigers and cheetahs are probably related. Each type of animal evolved differently, selecting certain characteristics that appear to have been of most help in ensuring survival.

Simply from a visual standpoint, you’ll notice immediate difference between Norway or Black rats and house mice. Rats are much larger. At maturity, they weigh about 12.35- 22.93 ounces (350-650 g), and have about a 9-11 inch (22.86-27.94cm) body length. They have long tails, which are an average length of 8 inches (20.32 cm). Their tails are thick and heavy.

A mouse, conversely may be one-tenth the weight of a rat, and weighs approximately 1-1.76 ounces (30-50 grams). Mice are shorter, about half the size of rats. They have an average body length of about 3-4 inches (7.62-10.16 cm), and their tails may be slightly more evenly balanced with their bodies, measuring about 3-4 inches. Mouse tails are very thin, and sometimes barely perceptible as compared to the much wider and longer rat tail.

At least in comparison of rats and mice in the species mentioned above, rats’ ears tend to be smaller in proportion to their heads, and they may appear larger, with more blunt features than do their distant relatives. Mice generally have delicate features and have more pointed faces that do rats. From a chromosomal standpoint, differences become even more striking.

Though there is relationship between rats and mice, their separate species are different on microscopic levels. Rats have a higher number of pairs of chromosomes, 22, as compared to the mouse’s 20 pairs. When kept together as house pets, they may create problems for each other. Rats may kill mice and eat mice, most commonly in undomesticated settings, and presence of rats in a home can seriously disturb a mouse. They may breed less or be panicked. If you want both rats and mice as pets, you should consider keeping them in separate rooms.

If you’re considering either animal as a pet, rats tend to be the better choice. They are usually more intelligent and relate better to humans than do mice. There are exceptions, and some wonderful mouse pets exist. In general, though, rats prove to be the better and more easily trained pet.

These differences between rats and mice can change depending upon different species compared. Both have fairly short lifespans in the wild, with about 70% dying before they are a year old. In captivity, lifespans may be similar. Mice might live longer, about five years, but many die at two to three years old. Rats may live about three-four years in captivity. The short lifespans of these animals may not make them ideal pets for young children.

Frequently Asked Questions

What are the main physical differences between rats and mice?

Rats are generally larger than mice, with thicker bodies, longer heads, and larger feet. Adult rats can weigh between 350-450 grams, while mice typically weigh 40-45 grams. Rats also have coarser fur than the softer fur of mice. Additionally, rat tails are thicker and less hairy compared to the thin, hairy tails of mice.

How do the behaviors of rats and mice differ?

Rats are more cautious and will typically avoid new things in their path until they get used to them, a behavior known as neophobia. Mice, on the other hand, are more curious and will often investigate new objects quickly. Rats also tend to be more aggressive and may live in larger, more complex social structures than mice.

Can rats and mice interbreed?

No, rats and mice cannot interbreed. They are different species with significant genetic differences. The house mouse (Mus musculus) and the Norway rat (Rattus norvegicus), for example, belong to different genera and have incompatible chromosomes, which prevents them from producing offspring together.

What are the differences in the diets of rats and mice?

Rats are omnivorous and have a more varied diet, consuming everything from fruits and grains to meat and fish. Mice are primarily herbivorous, preferring grains, fruits, and seeds. However, both rodents are opportunistic feeders and will eat a wide range of foods depending on availability.

How can you tell a rat's nest from a mouse's nest?

Rat nests are often larger and more complex than mouse nests. Rats will use a wider variety of materials, including twigs, paper, and cloth. Mice nests are smaller, often located in more secluded areas like wall cavities, and are made from finely shredded materials like paper or insulation.

What are the implications of a rat or mouse infestation?

Both rats and mice can cause significant damage to homes and are potential health risks due to the diseases they can carry, such as hantavirus and salmonellosis. Rats, due to their larger size, can cause more structural damage by gnawing through materials like wood and electrical wires, potentially leading to fire hazards.

AllThingsNature is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Tricia Christensen
By Tricia Christensen , Writer
With a Literature degree from Sonoma State University and years of experience as a AllThingsNature contributor, Tricia Christensen is based in Northern California and brings a wealth of knowledge and passion to her writing. Her wide-ranging interests include reading, writing, medicine, art, film, history, politics, ethics, and religion, all of which she incorporates into her informative articles. Tricia is currently working on her first novel.

Discussion Comments

By anon933052 — On Feb 14, 2014

Pet mice do not live five years. The average lifespan of a mouse is 1.5 to 2 years, even when kept in captivity and fed the highest quality foods and given the best of love and care. In 2009, a scientist bred a mouse whose growth hormone receptor was knocked out, leading to this mouse living to an advanced age of five years old. This was part of "Methuselah Project," a study about longevity. A mouse bought from a pet store or breeder will not live this long.

By afterall — On Jan 31, 2011

I have had friends with pet rats, and they swore they were some of the best pets ever. While I wouldn't want one, I can see why. They're much cleaner than their stereotypes suggest, and they don't have the same musky smells that other rodents, like ferrets, have even if they're clean. I think they also are not violent if raised in a nice home, though they could certainly defend themselves.

By hyrax53 — On Jan 28, 2011

While there are many physical differences between rats and mice, they do have some similarities. Both are more intelligent than you might expect, though rats are smarter. Also, both are good animals for psychological or biological experiments, though mice are usually preferred for this due to their smaller size.

By anon81335 — On May 01, 2010

please send me a list of all species of both rats and mice in the world.

Tricia Christensen

Tricia Christensen


With a Literature degree from Sonoma State University and years of experience as a AllThingsNature contributor, Tricia...
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