Although some may compare mice and rats as child and parent, these two rodents are different organisms. Their biology is different and their life history is different. There are key characteristics to distinguish the difference.
The body of a mouse will grow from 2” as a baby to 3 ½” when fully grown. Mice can weigh as little as ½ an ounce and grow up to 1 ounce. Mice can enter buildings through openings as small as ¼”. Mice will have several litters per year, each of 3–16 young; which can be born in 18-21 days after mating.
The presence of rats can be detected by droppings or evidence of fresh gnawing. Tracks can be seen in mud and on dusty surfaces. Runways and burrows may be found next to buildings, along pipes and uncapped sewers.
Rats have litters of 6to 12 young, which are born 21-23 days after mating. Young rats reach reproductive maturity in about three months. Breeding is most active in the spring and fall. The average female rat has 4-6 litters per year.