Help! My Hermit Crab is Out of His Shell and Won't Go Back In - What Do I Do?

One of the most frequent types of questions I get about hermit crabs that are out of their shells and won't get back in. Hermit crabs won't do this without a reason - the trick is figuring out what that reason might be and how to correct it. If you find your hermit crab suddenly out of its shell, it is important not to panic, but it is an indication that something is amiss. A list of reasons that this might happen and some ideas on steps to take can be found in my answer to "Help! My Hermit Crab is Out of His Shell and Won't Go Back In - What Do I Do?"