The average life span of a rat is one year. Mice mature rapidly and by 1.5 to 2 months of age are old enough to reproduce. They carry their young for 19 to 21 days and have 5 or 6 young per litter and 5 to 8 litters per year. A female mouse can breed again 2 to 4 days after giving birth. House mice breed throughout the year and do not show any seasonal breeding peaks.
Mice build nests of soft materials such as grass, paper, or cloth in hidden secluded areas.
Nests are usually 13 cm in diameter with a small entrance hole on the side. Mice are born naked with their eyes and ears closed. They develop rapidly, and in 2 weeks they are covered with hair, their eyes and ears are open and they are no longer totally helpless. In another week they begin exploring the nest area and eating solid foods. At 5 to 8 weeks of age the mice are independent and ready to breed.