Head to head
Brown Rat vs House Mouse
The brown rat and the house mouse are the two rodents that share human buildings across the world, and both are pests, both are lab animals, and both are in the same family. The confusion usually comes from a young rat being mistaken for a large mouse, so the key is to judge proportions rather than absolute size.
| Brown Rat | House Mouse | |
|---|---|---|
| Body length | About 20 to 25 cm | About 7 to 10 cm |
| Weight | About 200 to 500 g | About 15 to 30 g |
| Tail | Thick, scaly, shorter than the body | Thin, about as long as the body |
| Head | Blunt and heavy | Small and pointed |
| Ears | Small relative to the head | Large relative to the head |
| Droppings | Large, about the size of a raisin | Tiny, about the size of a rice grain |
| New objects | Wary; avoids them for days | Curious; investigates quickly |
| Water | Needs to drink daily | Can get by on water in food |
Rat vs Mouse: common questions
How do I tell a young rat from an adult mouse?
Judge the proportions, not the overall size, because a juvenile rat and a large mouse can weigh about the same. A young rat has a head and feet that already look too big for its body, a blunt muzzle, and a thick tail, and it feels heavy and solid for its length. An adult mouse has a small, neat, pointed head, very large ears, small thin feet, and a fine tail, and it feels light and delicate. The tail is a good check, as a mouse's tail is roughly the same length as its head and body, while a rat's tail, even on a youngster, is shorter than the head and body and noticeably thicker. Droppings nearby also tell you which you have, since they differ in size by several times.
Which is harder to get rid of, rats or mice?
They are difficult in different ways. Rats are individually harder to trap because they are neophobic, meaning they avoid anything new in their territory, so a fresh trap or bait station may be ignored for several days until the rats get used to it, and a trap that catches one rat may then be shunned by the rest. Mice are easy to trap but come in larger numbers and breed even faster, and because they need very little space and almost no water they can live deep inside a building far from any obvious sign. In practice, mouse infestations tend to involve more animals and more entry points, while rat infestations involve fewer but warier animals and often a burrow system outside. Both are best tackled by sealing entry points first.
Are rats and mice closely related?
They are in the same family, the Muridae, the largest family of mammals, but they are not each other's closest relatives within it. The brown rat is one of several Rattus species, and the house mouse is one of several Mus species, and the two genera diverged millions of years ago. They resemble each other because both are small, adaptable, fast-breeding, seed-eating rodents that independently became closely associated with humans and human food stores. Both have also become key laboratory animals, and comparing rat and mouse biology is a routine part of medical research, precisely because they are similar enough to be comparable but different enough to be informative.