Updated: Jul 14
Australian Land Hermit Crabs are Arthropods, this means that they need to moult their exoskeleton in order to grow.
So, what exactly does moulting mean? When a Hermit Crab moults, they shed their hard exoskeleton, this should not be confused with the shell, the exoskeleton is the hard skin located on the Hermit Crabs body. Their body does not contain bones like that of a mammal, it is made up of soft body tissues that are protected by their hard exoskeleton.
Moulting is an extremely sensitive and stressful time for a Hermit Crab, during this time the crab will dig down deep into the substrate and create a little, dark air cave where they will spend the following weeks or months shedding their exoskeleton, in which their new exoskeleton will be fresh and soft; this makes them quite the target for attacks, which is why it is so important to not overcrowd your tank. The Hermit Crab will stay in their cave until their new exoskeleton has hardened and it is safe for them to return to the surface.
This is why it is so important to supply deep, moist substrate for your Hermit Crabs to safely complete their moulting process.
The amount of time it takes a Hermit Crab to moult will solely depend on their size. The smaller the crab, the shorter the moult cycle; however, they will moult more often. The larger the crab the longer the moult cycle, in which they will moult less often than that of a smaller crab. If you wanted to put it into numbers, it could be anywhere from a few weeks to 6+ months, there is no set time frame, and it will differ for each crab.
Excessive Eating & Drinking - Leading up to their moult, a Hermit Crab will eat and drink excessively, this is done to build up their moult sac (a little sac located on their abdomen in which they store food and water for their moult) they use their moult sacs to survive for months on end while under the sand.
Excessive Digging - Hermit Crabs will start excessive digging and creating moult tunnels in the lead up to the big event. This is totally normal behavior.
Changing of Shells - This one is not a guaranteed sign, but sometimes Hermit Crabs will change into another, bigger or smaller shell before they go down for their moult.
Sluggish Behavior - Hermit Crabs activity during moulting is basically none, often before a moult, they can become quite sluggish and slow.
Eye Changes - Their eyes are usually a shiny black, leading up to moulting, their eyes may appear cloudy.
Freshly Moulted Signs
Hairy Legs - When a crab has freshly moulted, they will have very hairy legs.
Sharp Black Nail Tips - Those tiny little black nail tips will be razor sharp after a successful moult.
Colour Change - A freshly moulted crabs colour may be lighter or darker from before their moult.
Stages of Moulting -
Stage 1 (pre-moult) this is when the Hermit Crab will start to store fat in their moult sac in preparation of moulting.
Stage 2 (moulting) this is when the old exoskeleton will start to shed from the body.
Stage 3 (post-moult) the old exoskeleton has now shed, and the new, soft exoskeleton begins to harden. During this time, the Hermit Crab will consume their old exoskeleton and start to regain their strength. It is very important that they consume their old exoskeleton before they resurface. This is filled with calcium, vitamins and minerals.
How to tell the difference between a shed exoskeleton and a crab? If you find what looks like a dead crab without a shell, it may very well be shed exoskeleton. This will be empty, and if you squeeze it with your fingers, it should crumble in your hand. If it appears heavy and meaty on the inside, it is definitely a crab.
Do Hermit Crabs leave their shell during moulting? No, the Hermit Crab stays inside its shell during the moulting stage.
What happens if a moulting crab is disturbed by myself or another crab? This is a very dangerous time for your crab, it is vital that you do not disturb the crab during moulting by digging, touching or moving it. If they are found mid moult by another crab, they can often be consumed by the intruder.
How many types of moults are there? 2 - Below the sub moulting and surface moulting. A surface moult is an instant emergency and should be handled correctly immediately. You can read about surface moulting in our blog post here https://www.happyhermie.com.au/post/surface-moulting-a-hermit-crab-emergency
Will my Hermit Crab change shells after every moult? No, your crab will change shells whenever they are ready, at any stage.
What do I do if my crab comes up from their moult too early and they are still soft? If your Hermit Crab resurfaces too soon after a moult, they may appear very pale and soft. This makes them extremely vulnerable to attack. They should be isolated away from the rest of the crew until their exoskeleton has completely hardened and they have gained back their strength.
What diet should I offer my Hermit Crab after moulting to support their exoskeleton health? Lots of calcium! Cuttlefish Bone, Sand Dollar, Star Fish, Sea Urchins, Oyster Shell etc. Super foods filled with antioxidants and vitamins and minerals such as Bee Pollen, Blackstrap Molasses, Fruits and Vegetables and high carbohydrate and beta-carotene rich foods.
*A freshly moulted Hermit Crab (inside the shell) with their old exoskeleton.
*Hermit Crab moult sac (black bubble)
**Pictures supplied from Crab Street Journal and Krabitat.