Are you feeling crabby today? If so, cheer up! We’re going to learn about some interesting creatures that make great pets at home or at school.

Hermit crabs are crustaceans. Crustaceans are a class of creatures with segmented bodies and exoskeletons (external skeletons) that includes lobsters, shrimp and crabs.

Hermit crabs can live either on land or in water. They’re not true crabs, though.

In fact, they’re more like squat lobsters than true crabs. True crabs have abdomens protected by hard shells.

Hermit crabs have soft, exposed abdomens. This leaves them vulnerable to predators.

To protect themselves, hermit crabs search for abandoned shells — usually sea snail shells. When they find one that fits, they tuck themselves inside it for protection and carry it with them wherever they go.

This habit of living in a borrowed shell gave rise to the hermit crab’s name. Since hermit crabs often retreat completely into their borrowed shells for protection, some people think they act like hermits.

Hermits are people who live alone and do not interact often with others. Hermit crabs aren’t really hermits, though.

They tend to be quite social animals that enjoy living in groups. In the wild, they can often be found in large groups of 100 or more.

As hermit crabs grow, they often outgrow their borrowed shell. When this happens, they have to “shop” for a new one.

Hermit crabs can be very picky about the shell they choose. They want a shell that they can fit into completely in case they need to hide for protection.

Sometimes hermit crabs that live together help each other find new shells. When a new, large shell becomes available, hermit crabs have been known to form a line by it from largest to smallest.

The largest crab moves into the new shell. The next largest crab moves into the shell just vacated by the last crab and so on.

Hermit crabs sometimes like to “decorate” their shells. To help camouflage themselves and add an extra layer of protection, hermit crabs sometimes carry sea anemones on their shells.

Sea anemones are poisonous, so other creatures will usually avoid them and leave the hermit crabs alone.

Many people — and a lot of schools — keep hermit crabs as pets in aquariums. Hermit crabs are great for aquariums because they eat algae and debris to help keep the tank clean.

Most hermit crabs are fairly small. However, one land-dwelling hermit crab can get quite large. The coconut crab can grow to be up to three feet long and weigh nine pounds!

The coconut crab is unique in another way, too. When it outgrows the largest shell it can find, it grows a shell of its own.


34 Join the Discussion

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    • We’re glad you’re the first Wonder Friend to leave us a comment on today’s Wonder, Rahul! Way to go! We are super glad you learned some new things about hermit crabs today! :-)

    • We’re SO HAPPY to hear that you love Wonderopolis, Zane! We love it, too! There is always something new to learn and a new Wonder of the Day® to explore! :-)

  1. I’ve actually begun looking into hermit crabs since October… and lo and behold, here you provided information and a video! :) I actually went and checked out youtube videos of coconut crabs and hermit crabs searching for their bigger homes right after I read this article.

    I hope to be keeping a hermit crab (or two… or three!) as a pet, but I know even though they may appear “easy to take care of,” they actually require a lot to create their home environment, especially if you don’t live in a place with their ideal living situations.

    So yes, hello from the wintery area of Illinois! Thank you for providing something interesting every day for us to learn about!

    • Your comment just made our day, Jen! We enjoy hearing from Wonder Friends all over the world, and really appreciate it when they share a little about themselves (like you did)! You have a very mature attitude about the responsibility of taking care of pets! We think you would make a great caretaker to a hermit crab (or two… or three!). Have a WONDERful day and try to stay warm in wintery Illinois! :-)

  2. We loved the hermit crab video. We think hermit crabs are good pets. We never knew that hermit crabs were more like lobsters than crabs. Thanks for this new information!

    • Hello, Mrs. Rosenthal’s Class! Thank you so much for leaving us this great comment! We’re so glad you learned a new fact about hermit crabs today! :-)

  3. We loved the race! It was really interesting watching the big hermit crab race the little hermit crab for the win. We were very happy for #2.

    We didn’t know that hermit crabs have coloured shells, or that they could decorate them with sea anemones! What a cool word.

    We also thought the video of the crab “shopping” for a new shell was very cool.
    We loved the sound effects! Thanks, wonderopolis for being wonderful. :)

    • Well, we think YOU guys are pretty Wonderful, too, 5A in Gibbons! We really appreciated your comment and all the neat things you thought about the video for this Wonder! If you like the word “anemones,” keep your eye out for a special Wonder of the Day® in the near future! :-)

  4. I absolutely love hermit crabs, they have such a funny look in their eyes.
    Once while diving, we saw a small one that spotted a bigger shell. He immediately went investigating but to his absolute horror there was a much bigger one already in there. He raced away like greased lightning.

    Another time, we took one up to examine it closer. The shell was too small and he fell out of it on my glove. We gave the shell back and very quickly he jumped back in. It was such a funny sight to see it cling for dear life with his two smallest claws. Like, if you want to pull your hood over your eyes.

    • Thank you so much for sharing your personal connection to this Wonder of the Day®, Klara! Your stories about seeing hermit crabs while you were diving are AWESOME! What a great experience for you to see them in their natural habitat! :-)

    • Even though this Wonder wasn’t what you thought it was going to be, we still hope you learned some new things about hermit crabs, San! Thanks for hanging out in Wonderopolis today! :-)

    • We’re glad you liked this Wonder, Mak! Thank you for always leaving us such enthusiastic comments! We appreciate you! :-)

    • Hello, Elango! We’re glad you are excited about hermit crabs and hope you learned lots of new things about them by exploring this Wonder of the Day®! :-)

    • We’re glad you think Wonderopolis is entertaining, Albert! Thank you for stopping by this Wonder of the Day® and leaving us a comment! :-)

  5. Hi,

    I never really knew that a coconut crab can be 3 feet long and weigh 9 pounds. I found it interesting how they put poisonous stuff on their shells.
    Did you know that the cause of hearing the ocean in a seashell is because the veins in the shell vibrate?
    Thank you so much for making me wonder!

    Team Clark 19 :)

    • Thanks for teaching US something new about shells today, Team Clark 19! We never knew that before! We think a future Wonder of the Day® about why we hear the ocean in a shell would be a GREAT idea…thank you for sharing your knowledge! :-)

  6. I have a hermit crab that is pretty big. I looked for some larger shells for him and I could only find the kind that are more angular than circular and now his legs don’t fit all the way in the shell. Will he be ok until I can find him a circular one? Thanks!

    • Hi there, Mara! We bet it’s SUPER cool to have a pet hermit crab! While your hermit crab protects itself from harm and predators with its shell, your pet is not it its natural habitat… but it still needs a proper home. However, crabs can be picky about shells, so offering your pet two or three shells that are bigger than the crab will help. You don’t want your pet to be cramped! :)

  7. I have just recently gotten 2 Hermit crabs I want to get one of those clear shells for it dose anyone know if I am waisting my time? As I have read up on them & they like to be well hidden? I only have them In a tub I was wondering if you need to filter the water like a fish tank? I found out they are quite clever one of them I left the lid off it and one of them built the sand up right to the top of the
    Tank. They must be clever cause I have herd them digging away for nights & Nights. I think they must get board? Dose anyone know how to get them to make baby’s?

    • Thanks for sharing your thoughts, Anthony Francis! Maybe you could find a book about hermit crabs at your library. They are interesting creatures! :)

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Have you ever wondered…

  • Why do hermit crabs live in borrowed shells?
  • How are hermit crabs different from true crabs?
  • Are hermit crabs really hermits?

Wonder Gallery

hermit crab_shutterstock_72446029Vimeo Video

Try It Out

Are you an introvert or an extrovert? Everyone has a unique personality.

Introverts tend to keep to themselves and focus inward. Sometimes they are like hermits if they live alone and are socially isolated.

Extroverts, on the other hand, focus on others and are very outgoing. Extroverts prefer to be around others most of the time, whereas introverts might rather spend time alone with a good book.

Whether we’re introverts or extroverts, we all crawl into our own emotional shells from time to time. When things stress us out, we may retreat from others to protect ourselves from getting hurt.

For example, if we don’t get invited to a party, we might convince ourselves that we didn’t really want to go anyway. We may avoid others to avoid feeling bad about not being invited.

Do you remember times when you’ve put an emotional “shell” of protection around yourself? We all do it from time to time.

Most of the time, there’s at least one area of our lives where we’re hiding inside our shell. Try to figure out areas of your life where you might be hiding inside your shell.

When you identify such an area, think about how you might be able to come out of your shell just a bit. It may be as simple as trying new things, meeting new people or making new friends.

You can get started right now! If you’ve never commented on a Wonder of the Day before, it’s time to come out of your shell and tell us what you think.

You can comment below, email us, post a comment on Facebook or even Tweet us a comment. We can’t wait to hear from you!


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Explore Science NetLinks’ How a Blue Crab Changes as It Grows lesson to learn about the changes that a blue crab goes through during molting.


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