How a Rainbow Crab Moults Its Exoskeleton
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How a Rainbow Crab Moults Its Exoskeleton

Real life experience of a Rainbow crab just after moult.

If you have every wondered just how these crustaceans manage to climb out of their bodies then I am about to explain.

 What is a crustacean?

 Crustacean is the name given to a very large, diverse group of arthropods. You will know them as crabs, lobsters and the like. Basically it’s a creature with an exoskeleton.

Photograph by author. Young Rainbow crab.

 What is an arthropod?

 This is the word that describes an invertebrate creature with an exoskeleton and a segmented body with jointed legs.

 What is an exoskeleton?

 True crustaceans have what is called an exoskeleton. Basically their hard skeleton is on the outside of their flesh and organs as apposed to inside like ours. Of course as these rainbow crabs only start off very small and grow very rapidly in the first few years of life, they have to get rid of their old exoskeleton so they can grow. They will moult every few months as youngsters but this slows down to about once a year as they reach maturity, which is when they are aged around three to four years old.

Photograph by author. Rainbow crab.

 The first signs of the Rainbow crab going into moult will be that he will stop all eating. They can go several months without eating, with no side effects or consequences to this voluntary starvation. They will only moult when they feel safe. As they are land crabs (which means they live on land but they still do have to go into the water to take oxygen out of the water via gills which live on the outside of their bodies) they may seek the shelter of a riverbank burrow, a large rock formation or some hidden water in the wild. If you keep one as a pet make sure he has lots of calm hiding places to choose from.

 What happens to the shell?

 It is not just the shell that gets a make over but the whole crab. If your crab has suffered any injury and lost a limb it will replace that limb when its new body emerges from the old skeleton.

Photograph by author. The opened shell and limbs. 

 Although I have never had the privilege to witness my crab actually emerging from his old skeleton I have seen him a few minuets later, just after he has come out.

 It is a very stressful time for a crab because when he emerges his body is soft, he has no protection at all until his exoskeleton hardens which can take a couple of days. You must never disturb them in the middle of moult it could kill them.

Photograph by author. The new shell and limbs are still soft.

 First of all the shell brakes open around the middle. Just like an Easter egg to reveal the goodies inside! This enables him to then pull all his limbs free from his old skeleton casings and squeeze his body out. The hairs on the limbs are left still protruding from the old discarded skeleton, the only thing that doesn’t get renewed are his stalk eyes because they obviously just poke through the skeleton and are not actually part of it. I leave the old skeleton in with the crab so he can eat it and replace lost calcium.

Photograph by author. He hides behind his rock.

 I find this a truly amazing happening and will never get board of seeing the new out come each time he moults. I hope you enjoy the photographs of my Rainbow crab Rufus.   

Photograph by author. He has now ready to start eating again. Ham or cucumber?

 Photograph by author. Colours all back to normal now his shell is hard. 

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Comments (16)

Your crab is cute. Whatever happens don't adapt to his mentality...A nice post my friend.

Terrific write Lisa, very informative and interesting! Crabs, lobsters and other crustaceans always remind me of the bugs of the ocean. For example a lobster looks a lot like a scorpian. You have my vote and buzz as always my friend!

Amazing pet Lisa, my first knowledge on rainbow crab.

Cool! You name it Rufus! I'll have the ham please! :D

This was a brilliant discussion. I've always found crustaceans fascinating.

ok- crabs just can be my pet peeves:D I felt weird just looking at the pictures, lol! :)

Nice article with great pictures!

A good discussion, Lisa. Dugg this one ;)

Make all the more excellent by the use of pictures. Ham or Cucumber? is that what they eat? wow..

It's pretty amazing evolution for these crabs to replace a brokened limb in this process. "Rufus" looks pretty cool and great photos of your pet. I had no clue people care for these Rainbow crabs as pets. Pretty unique pet, for sure. Well written article and very informative on a interesting process. Great work and enjoyable read.

That's great having a personal encounter of a molting crab. Nice documentation.

Nice crab and very good article. Well done

I love the rainbow crab. They are really amazing. Read this one again and posted at FB xx Thanks for all your support :)

Thank you sweetie x

Heather Laboda

Hi, my halloween moon crab (a crab similar to Rufus) has stopped eating and pooping for about a week now, I am concerned. Are there any other signs to look for if he is going to molt. I have noticed that he is taking on more water and his gills (the white stuff on his backside and around his legs) seem to be more enlarged. His activity is still somewhat normal for his personality (skittish, likes to pinch), but he just doesn't seem to be his usual crabby self. He also seems more sluggish when moving around. I have had him for a year and I have never experienced him molting. His name is munchy, because he normally eats anything and everything I put in his crabitat. Unfortunately there aren't any pet stores in my area that are knowledgeable about these little crabs.

sadly the crab in the photos died a couple of months ago age 8. I was devistated and still miss his funny ways, so I am reposting all the articles about him.