I have these in my hisser tank. When the substrate dries out I tend to see them more, when it's really damp then they tend to drown. They are kind of annoying but as you said, harmless. Other than messing up your substrate I don't see them as a problem.Looks like it could be the moths I have in mine. My dubia and giganteus colonies are full of these moths. Did you find in in sort of a silk-lined tunnel thing? I haven't noticed any adverse effects, but it sure can be annoying to have 5 moths fly out every time you open a bin.