Approximately how many litters can a female mouse produce in a year?

• A. 5
• B. 10
• C. 15
• D. 20

Answer: (B)

Mice reproduce very quickly because their reproductive cycle is short and they can become pregnant again soon after giving birth. Gestation lasts about 19–21 days, and after birth the pups are weaned in roughly three weeks. With favorable conditions year-round, a female can cycle through roughly four to five litters in a year, which adds up to about ten litters annually. This rapid turnover is why mice are such prolific breeders in pest situations. The other options would imply fewer or more cycles than the biology typically supports in a year under good conditions, so around ten litters is the best approximate.