How do I tell if is time take a forming beetle out and put it in the cage?

I am watching a beetle larva for a friend. Will it dig its way to the top, or do I take it out? If it is the latter, when is it safe to take out? (I am worried if I wait too long I will kill it, but if I do it too early, I could kill it too.) Don't they normally just dig themselves out in the wild?