Life Cycle of the Norway Rat

The Norway Rat (Rattus norvegicus) is a large, common rat characterized by its thick, heavy fur, small ears and eyes, blunt nose, and short tail relative to its body. It can live for approximately 1 year, but during its relatively short lifespan, it will go through many stages.

A female Norway rat will give birth to an average of 9 pups, all 1-2 inches long, after a gestation period of about 3 weeks. The pups are born deaf, hairless, and blind, and are entirely reliant on their mother for food and protection.

After birth, the rats will remain deaf and blind for 4-5 days and stay hairless for another 1-2 weeks. By the second week, the Norway Rat will have gained the strength to walk independently, and by the 5th week, it will finally enter the juvenile stage.

During the juvenile stage, these rats will spend roughly another 2 weeks reliant on the mother, after which they will be fully weaned and begin foraging for food on their own, reaching around 10 inches in length by the time they enter adulthood.

A Norway Rat will reach sexual maturity by 8-10 weeks in total, only growing another 1-2 inches in the adult stage. After they are developed enough for reproduction, the cycle will start all over again. Paired with their rapid growth, the Norway Rat’s 1-year lifespan allows it to reproduce many times —about 3-6 litters per year —making one rat capable of causing an entire infestation in a relatively short time.