The new shell is not right. The hermit crab may not be comfortable with the new shell, for example, it may be too big or too small. It can also be too easy or too hard to carry.
The old shell is still preferable despite being damaged. The old shell may provide better protection or it may be more familiar and comforting to the hermit crab.
Stress. If a hermit crab is feeling stressed, it may return to its old shell as a way of coping.
Health issues. If a hermit crab is sick or injured, it may retreat to its old shell and stop moving around as much as a means of conservation energy.
Shedding. In most cases, the molting process doesn’t finish in one day and in some cases, the hermit crab's body is to soft for the new shell. In this situation, the crab may return to its old shell to wait until the new shell hardens.
If your hermit crab does return to its old shell, don't worry. Just keep an eye on it and make sure it is eating and drinking. If it doesn't return to its new shell in a few days, you may need to take it to a veterinarian.
Here are some ways to help your hermit crab choose the right new shell:
* Offer a variety of shells of different sizes and shapes.
* Make sure the shells are clean and in good condition.
* Place the shells in a safe location where the hermit crab can easily find them.
* Be patient. It may take some time for the hermit crab to choose a new shell.
If you are not sure what size hermit crab shell to get for your hermit crab, you can use the following general rule of thumb: the shell should be about the same size as the hermit crab's body.