How to Tell the Difference Between a Girl & Boy Mouse

Mice are very cute and interesting pets. They are clean and friendly, but they can multiply very quickly if you accidentally put a male and female together. Sometimes pet stores make mistakes if the sales clerk is inexperienced or distracted, so it's best to learn to sex the mice yourself so that you can be sure which sex you're getting. If you have a litter of mice and need to find them homes, you can identify their sex even when they are newborn.

Things You'll Need

Magnifying glass (optional)

Instructions

- 1
  
  A very tame mouse will sit in your hand without trying to jump away.
  
  Pick up your mouse and hold it gently but firmly. Try to make the mouse feel safe, but hold it so it cannot jump from your hands and get hurt.
- 2
  Turn your mouse over gently, supporting its head, neck and spine. Again, make sure it can't jump from your hands.
- 3
  Push the fur aside on the abdomen to see if there are nipples. Only females have nipples.
- 4
  Look at the distance between the anus and the urinary/genital opening. In females, these opening are very close together, but in males the penis is located a distance from the anus, on the lower abdomen.
- 5
  Look at the groin area, between the mouse's back legs. If a male is old enough, you will see the testicles. A mouse's testicles are surprisingly large compared to its small body, so if you don't see them, you have a female or an immature male. If the male is old enough to leave its mother, it should have visible testicles.