Molting is a natural process for hermit crabs. In order for a hermit crab to grow it must molt. Molting may occur once a year for larger hermit crabs or once every few months for smaller (tiny crabs).
To know if your hermit crab is preparing to molt look for these signs:
- The hermit crab will probably become lethargic (it won’t move much).
- Your hermit crab will start digging.
- The hermit crab’s coloring may become ashy, the coloring probably won’t be as vibrant.
- Your hermit crab will probably eat a lot of food and drink a lot of water.
- The hermit crab may develop some eye crust or the hermit crab’s eyes may look cloudy. This will go away after a molt.
- Your hermit crab will develop a molt sac. This molt sac holds water and helps to break the exoskeleton when the hermit crab actually molts. The molt sac doesn’t store food.
- If your hermit crab is missing a limb it will probably develop a gel limb. Once your hermit crab molts the missing limb will be regenerated, but it may be smaller than the original.
If you notice these signs you may want to isolate your hermit crab in what we call an isolation tank. This is usually a smaller tank with lots of moist sand or eco earth, some water (both saltwater and dechlorinated water), food, and a hiding place. Make sure that the humidity is 78-80% and the temperature is around 78-80 also. Some of us, myself included, allow their hermit crabs to molt in the main tank without problems. This is really a personal choice. If you don’t have a good isolation tank with gauges and proper conditions then you should probably leave them in the main tank to molt. Moving them into a plastic box without good heat and humidity really isn’t good.
The hermit crab molting process may take several weeks to several months. Your hermit crab should dig under the substrate when it’s actually going to molt; if it doesn’t you may be using the wrong kind of substrate. When a hermit crab molts above ground it is called surface molting. Gravel, rocks, wood chips, and pebbles are not good molting substrates. It is better to use sand, forest bedding or eco earth as a substrate in your tank. Sometimes a hermit crab will surface molt even with the right tank conditions. If a hermit crab surface molts in your main tank I would recommend isolating the hermit crab in its own tank immediately. Move the exoskeleton with the hermit crab into isolation. When a hermit crab molts on the surface other hermit crabs may attack it. Since the hermit crab is very soft immediately after the molt it will not be able to protect itself from other hermit crabs.
Once your hermit crab has dug under the sand avoid the urge to dig it up to check on it. Leave your hermit crab alone to molt. Keep the tank warm, humid, and dark. Your hermit crab knows how to molt, there is nothing you can do to help. 
Your hermit crab may be under the substrate preparing to molt, molting, and recuperating post-molt for up to eight weeks. I know, that’s a long time to leave them alone. Larger crabs will typically take longer to molt than smaller hermit crabs. When your hermit crab resurfaces it will be very hairy, have very sharp nails, and if it was being provided a good diet its coloring will probably be very vibrant. Here is a really good picture of a hermit crab’s sharp nails after a molt.
When your hermit crab molts it sheds its exoskeleton like a snake. It then eats its exoskeleton post molt to help it recover. Don’t freak out if you find hermit crab limbs in your tank, it’s probably hollow exoskeleton that your hermit crab didn’t eat. Leftover exoskeleton that your freshly molted hermit crab didn’t eat can be given to your other crabs, it’s good for them! It’s also a good idea to keep other calcium sources in your tank for fresh molters; cuttlebone, crushed oyster shell, and eggshells are good sources of calcium for your hermit crabs.
It will usually take your hermit crab several days to a couple of weeks to fully harden and be active again. If you isolated your hermit crab, you don’t want to put it back into the main tank until it is eating regular food and climbing around the isolation tank like it wants to escape. You will probably find that your hermit crab is very shy post molt and seems like it is afraid of its own shadow, this is normal and it takes about a month for the hermit crab’s normal personality to return.
Just a warning. Many new crab owners think that their hermit crab is dead when it has actually molted. If you come across a crab that looks like it has fallen out of its shell check the shell carefully to see if in fact there is a smaller crab tucked in the shell. When a hermit crab has molted the soft abdomen will not fall out of the shell, only the hard exoskeleton will shed.
Visit Stacy’s photo gallery for pictures of freshly molted hermit crabs and exoskeletons.
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