Just thought of something else... if this is indeed new behavior for Yoshi, and if Yoshi is indeed a little lady, she may be wanting to lay eggs. Even if there have been no males around, she could be carrying an infertile batch (slugs). Is she at all chubby? Feel any unusual round bumps? Is she also digging or disturbing her substrate more than usual? If you suspect this at all, you need to set up and egg box for her that she'll feel secure laying eggs in. If she is too stressed or doesn't have a spot to lay them, she could get egg-bound, which is NOT good. I wouldn't bet that this is what is going on, and even f it is the odds of her getting egg-bound are even smaller, but it is something to be aware of...