While mice and rats share a few common characteristics, the major differences between them is their size and diet. The typical house mouse is 2-4” in length, as opposed to the Norway rat or roof rat, which can measure up to 9” in length. Both mice and rats are omnivores, but rats will eat anything, and generally prefer meat, pet food, fish, and stored cheeses. Mice prefer grains, fruits, vegetables, seeds, and nuts.