One of my two new mice, Val, was recently bought at Petco from a selection of other female mice. She was the smallest one there - barely an inch long excluding her tail - and has a brown coat and big black eyes. I've been checking on all of my mice every morning, afternoon, and evening to make sure that they're all healthy and settling comfortably into their new home (I just got them last Thursday) and noticed that Val liked to stay inside of her plastic 'igloo' rather than join in any festivities with her other mouse-cage-mates. Should I be worried about her staying inside of her igloo so much? I watch her to make sure that she eats, and she uses her water bottle like normal - however, I'm beginning to wonder if she gets exercise on the exercise wheel in the cage, or runs around like her other friends. On her first day here, she tested out the wheel (a Silent Spinner) and seemed to enjoy it, and now, I have to reach into her igloo, take her out, and make sure she's okay. She likes to sleep, and eats/grooms herself inside there as well. When I first pick her up when she's a bit groggy, she'll move slowly, but then speed up a tiny bit before I put her back. But, I mainly pick her up in the early evening/morning, so she probably isn't at her most active stage yet. After all, they are nocturnal! Is she just young and getting accustomed to her new home? Any advice would be fantastic - thanks!

I have noticed that very young mice seem lethargic. I think this is instinctive behavior avoiding possible predators when too small to escape fast enough, and wants to sleep in to get bigger and stronger. Maybe also territorially threatened by the bigger ones.

Let me start off by saying Val sounds adorbable, holy crap!! pets question and answers,www.5d2d.com
Sounds like you just have a lazy mouse. I had a hamster before, Steve, and he constantly would be in the little house. There shouldn't be anything to worry about unless you start noticing physical changes on her body or anything else. (By your description, I don't think you'd ever have that problem. You're a good parent. :D)

I love hamsters and mice <3