Q: I have a mouse that is 4 months old and completely hyperactive. She runs on her wheel for hours at a time (an average of 20ish hours a day) and sometimes just runs around her cage as fast as she can, and up and down the wire. She is also rather aggressive toward us and another mouse that we have (also female). The mice are now in separate cages due to the one’s hyper behavior. The hyper mouse wasn’t always like this, and the behavior appears to be getting progressively worse. Is this completely manic, hyperactive behavior something to worry about?
A: Mice are typically very active at night and often spend several hours on their wheels, but the type of extreme hyperactivity you describe is not normal. For now, leave the mice in separate cages and find another female companion for your non-aggressive mouse. Female mice are very social animals, and they are happiest when they are housed in a small group with other females.
The real concern is that your mouse is also being aggressive toward you and her cagemate, which is very unusual for females. It’s possible that these behavior changes are the result of a medical issue. If the behavior continues, or if the aggression toward you increases, seek treatment from a veterinarian who is good with small animals.