Crabs, like all crustaceans, grow by molting. Molting is the process of shedding the hard outer shell in order to grow a larger one. This fascinating process allows crabs to increase in size despite having an exoskeleton that does not grow with them.
What Happens During Molting?
Molting occurs in several stages:
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Pre-Molt Stage: In preparation for molting, the crab reabsorbs some of the calcium from its old shell and secretes enzymes to separate the inner soft layer from the hard outer shell.
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Molting Stage Right before molting the crab absorbs water to expand the old shell. This causes the shell to split open along predefined lines. The crab then extracts itself from the old shell, starting with the rear and working its way forward. This can take 15 minutes or more.
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Post-Molt Stage After molting, the new soft shell begins to harden. Initially the crab is vulnerable but over the next few weeks the new shell will fully harden and provide protection.
Why Do Crabs Need to Molt?
There are several key reasons crabs molt:
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To grow larger – Molting enables growth despite the confines of a rigid outer shell,
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To mature sexually – Crabs molt more frequently when younger, but must reach a certain size through molting before becoming sexually mature adults.
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To regenerate lost limbs – Molting allows crabs to regrow lost legs and claws over successive molts.
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To rid of parasites and fouling – The old shell is discarded along with any attached organisms.
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To repair damage – Flaws in the old shell are shed during molting.
What Happens to the Old Shell?
When a crab molts, the entire exoskeleton is discarded, including the hard upper shell, limbs, mouthparts, antennae, and even the delicate gill structures. Only the soft inner layer remains.
While molted shells may appear intact, they are quite hollow and lightweight compared to a whole crab. The old shell provides important calcium to help harden the new one.
How Often Do Crabs Molt?
Molting frequency depends on the age and stage of growth. Young crabs may molt every few weeks, while older crabs molt less often.
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Young juvenile crabs molt frequently to support rapid growth.
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Subadults molt seasonally, a few times per year.
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Adult crabs molt only once annually, or in some cases even less often.
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After reaching full size, crabs molt mostly for reproduction and limb regeneration.
Molting and Reproduction
Molting is closely tied to reproduction in crabs:
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Females mate only after molting, when their new shell is still soft.
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Male crabs may molt in preparation for mating and to regenerate mating claws.
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Female crabs brood eggs for several months after mating and molt again after the eggs hatch.
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Molting resets the cycle, allowing for a new brood in the next season.
Difficulties During Molting
Molting is a complex process that does not always go smoothly. Issues can include:
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Failure to fully extract from old shell, which can be fatal.
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Problems regenerating lost limbs or repairing damage.
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Shell abnormalities that hinder movement, feeding, and protection.
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Parasites that attack while the new shell is soft.
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Cannibalism by other opportunistic crabs.
Watching a Molt in Action
Few sights in nature are as fascinating as witnessing a crab emerging from its old shell in real time. Some great places to observe molting crabs include:
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Public aquariums with crab exhibits during molting seasons.
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University marine biology laboratories that study crustaceans.
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Crab pots and tanks at commercial crabbing facilities.
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On shore at low tide around sheltered coastal inlets where young crabs congregate.
With a little patience, you may be lucky enough to see a crab molt up close in the wild or in captivity. It’s a unique opportunity to observe this stunning biological process that enables crabs to grow, develop, and survive within their hard external skeletons.
Social Behavior and Tankmates
These crabs have been kept with fast-moving shrimp or small fish, but slow tankmates will likely be preyed upon; providing ample space is essential if attempting a mixed-species enclosure.
One male with two females is a common ratio to reduce territorial disputes. Each crab has a different personality, and females tend to be generally peaceful and more tolerant of one another.
More space means less conflict. Avoid aggressive fish or other animals that could injure or outcompete the crabs. A healthy mix of land and water encourages natural behaviors like burrowing and hiding.
Tank Lighting and Decor
A blue RGB strip light not only enhances their natural color while also mimicking twilight conditions. Bonsai soil mixed with leaf litter works well for the land section, and rocks or driftwood create more hiding places.
Crabs are escape artists by nature, so be sure to cover every potential exit. Providing plenty of cover helps reduce stress and aggression, especially if youre keeping vampire crabs in small groups.
When Do Crabs Molt? Understanding the Molting Process in Crustaceans
FAQ
What triggers molting in crabs?
When the crab is growing too big for it’s shell, cell pathways are triggered and messages are sent telling the molting process to begin. As mentioned before, there is a lot to this process, and it doesn’t just entail the molt, or shedding of the exoskeleton.
How often does a crab usually molt?
A crab will molt about six times during each of its first two years of life.
How do you know your crab is molting?
A molting crab appears quite limp and lifeless, and the body is often partway out of the shell.
Why can’t crabs eat when they molt?
Crabs that are molting are not concerned with food and digestion. Before they molt, they store up food and water. Once they are under the sand, they live on their internal storage.