A mouser is a cat that's especially good at catching mice. Some cats have a strong hunting instinct and spend their time stalking, chasing, and catching mice around barns, houses, or farms. A skilled mouser keeps buildings free of rodents that might eat stored grain, chew through walls, or spread disease.

For centuries, people kept cats specifically because they were excellent mousers. Before modern pest control, a good mouser was valuable on a farm or in a shop. Even today, some businesses and homes with mouse problems will adopt a cat known for being a talented mouser rather than using traps or poison.

Not every cat makes a good mouser. Some cats are too lazy or too well fed to bother hunting. Others lack the patience to sit still and wait for mice to appear. But a natural mouser will spend hours watching a mouse hole, ready to pounce the instant something moves. These cats may bring their catches to their owners, like a proud trophy of their hunting success.

The term can also refer to any animal that hunts mice, though it's most commonly used for cats.