Why do Hermit Crabs need Shells?

What is a Hermit Crab and How does it develop? What is their Size? Do they have Shells at Birth? What is Shell Behavior? Can they Survive without a Shell?
why do hermit crabs need shells

Every animal has their defense techniques and body parts. You must have seen turtles hiding in their shells when they are in danger. Pigeons have a different sense of defense when they are in danger, they close their eyes, believing when they re-open their eyes the danger will pass. Similarly, crabs also have their defense patterns and methods. Today you will get to know about natural hermit crab shells and why do hermit crabs need shells.

1. What is a Hermit Crab?

They belong to the Paguroidea superfamily in the kingdom of Animalia. They are anomuran decapod crustaceans who have mollusk shells. It has a soft asymmetrical abdomen. (Also read Slug Vs Snail)

2. What are its Types?

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Depending on their habitat, these crabs are divided into two groups, namely land and aquatic hermit crabs.

  • Land hermit crabs spend most parts of their life on land but occasionally visit oceans and other nearby water bodies. About 15 species are considered terrestrial hermit crabs.
  • Aquatic hermit crabs include the Clibanarius fonticola specie. It is the single species of marine hermit crab that spends most of its life underwater and rarely walks on land. Also, check out 10 Types of Crabs.

3. How do Hermit Crabs develop?

They develop in different stages and the initial 2 stages take place within the eggs, namely nauplius and protozoa. The 3rd stage is zoea and most of the eggs hatch at this stage. At this larval stage, their appearance is not like a crab and they have the following features,

4. What happens after the 3rd Stage?

The zoea stage is followed by various zoeal moults which means their body parts break, change shape, and reform several times before they reach their final larval stage. The final stage is known as megalopa. Also, check out what is Blobfish (Psychrolutes marcidus?)

5. What is the Size of a Hermit Crab?

A small hermit on the land: why do hermit crabs need shells 5

Before you know why do hermit crabs need shells, note that the size and shape of the hermit crabs depend largely on their species. They can be as small as a few mm or as large as a coconut with their shell. One such crab is the Coconut crab, which is true to its name in consideration of its size and weight. It is 3 feet (36 inches) long and weighs up to 9 pounds (approximately 4 kilograms). (See 12 Catfish Whiskers Facts)

6. Do they have Shells at Birth?

No, they are born without shells. The fragile exoskeleton is exposed and to protect it from predators, they find shells and get into them. (See 21 Healthiest Fish for Fishetarians)

7. Where do these Natural Hermit Crab Shells come from?

The shells of hermit crabs are the abandoned shells of marine gastropods. They can naturally create shells. Clams, snails, and other marine species of the phylum Mollusca produce shells. When the mollusks die, they give out a strong odor that attracts the hermit crabs. Must read the 15 types of Snails and facts about them.

8. Do they Grow according to their Shells?

An undersized shell affects their growth, a well-fitting shell encourages their speedy growth. If the shell is too large, then the crab will stick to its old shell. (See Where do Red Pandas live in USA?)

9. How big the Shell should be?

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As the hermit grows large with age, it needs to change shells. They get into the new shell and leave it when it outgrows. The size of the shell depends upon the size of the hermit crabs. (See Are Sand Dollars Rare?)

10. Why do Hermit Crabs need Shells?

Hermit crabs have a very fragile body and to protect the weak exoskeleton they need shells. The shell acts like their home and their defense mechanism. Their paper-thin abdomen stays safe from sharp objects while they crawl in the wild. (See 45 Types of Fish)

11. How are they attached to the Shells?

Nothing is binding the crabs to their shells. It is like a cap which they wear and take off easily. The uropod (small a leg-like structure located towards the back of the abdomen) grips the interior of the shell by spiraling alongside the interior of the shell. (See What is the Biggest Thing on Earth?)

12. Which Shells do they prefer?

According to the researchers, hermit crabs choose the shells which matched their environment the most. Also, they will examine the safety of their surroundings and then take up the new shell. It is because they are vulnerable without shells and cannot take a risk in changing the shell even if it is of the right size. (See Are Sea Anemones Plants or Animals?)

13. What is Shell Behavior?

Every hermit crab checks an empty shell, if the shell fits perfectly, then the crab leaves its old shell and shifts to the new one. If the shell is too large or small, the crab waits near the shell for any other crab to visit and do the size check.

While discussing why do hermit crabs need shells, you must understand this shell behavior. This process carries on till 20 crabs, holding onto each other in a line in descending order. No sooner than the crab in the perfect size for the new shell arrives, all the other waiting crabs begin exchanging their shells with each other. This process ensures the right-sized shell for each crab. (See 20 Largest Zoo in the World)

14. Do they fight among themselves for Shells?

Yes, there are situations when hermit crabs get into fights instead of forming a line and trying individually the new shell. In the following situations, crabs are witnessed getting into a fight.

  • If the hermit crab is interested in any pre-occupied shell,
  • If the shell is broken,
  • If it has been roaming without a shell for a long time and needs immediate protection, and
  • If there are no other shells available for shifting. (See What Are Shark Teeth Made Of?)

15. What if there are no Shells available?

A large red colored aquatic hermit: why do hermit crabs need shells 4

In cases when there are no seashells for crabs to claim, they take up any possible thing in sight, like any type of debris, custom-made shells, or tin cans. But this behavior often puts their lives in danger because the slippery debris is like a death trap for them which they can enter easily but there is no escape from it. The reasons why do hermit crabs need shells, are to create a death cycle because the old shell abandoned by the crab attracts new crabs and this makes the cycle going. (See When is it Safe to Remove a Wasp Nest?)

16. Can a Hermit Crab live without a Shell?

As you already know why do hermit crabs need shells, you must be aware that shells protect their fragile body and without shells, they need special conditions and parameters to survive.

So, today you got to know why do hermit crabs need shells and from where natural hermit crab shells come. It is time to share this information with your friends and family to enhance their knowledge about the hermit if they are planning to keep one as a pet. (See Why do Penguins not Fly?)

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