Sacculina are Pretty Much My Favorite Parasite

Maggie Koerth-Baker is a guest blogger on Boing Boing. A freelance science and health journalist, Maggie lives in Minneapolis, brain dumps on Twitter, and writes quite often for mental_floss magazine.

So one of the chapters in Be Amazing is dedicated to teaching you how to be a better mooch. Naturally, the focus is on parasites.

Just focus on that cute little, panhandling filarial worm, while I tell you about something far less adorable.

Sacculina are one of those creatures that are both absolutely fascinating and also relatively decent evidence against the existence of a loving deity. Think of them as nature's equivalent of Dracula, on the hunt for a Renfield.

Actually more of a barnacle with a parasitic bent, the sacculina starts out life as a weensy, free-floating organism, swimming about the seas. Although she spends her early life footloose and fancy-free, what the female sacculina really wants is to meet a nice crab and settle down. What the crab wants never really factors into the equation.

Once she finds a suitable crab, the sacculina swims around to the belly of the shellfish and, using a sharp hollow point on her exoskeleton, injects herself into the crab's flesh, leaving behind an empty husk. Inside the crab, the sacculina begins to take over, burrowing long, nutrient-sucking tendrils into every part of the crab's anatomy, from the eyestalks to the claws. As she does this, the sacculina changes the crab's behavior; effectively neutering it, preventing it from growing and winnowing down its once-vast list of interests to a single hobby: Eating. After the sacculina picks up a mate or two, the crab will even spend what little energy resources it has helping to tend her baby parasites and giving them a good start in the world. Now entirely under her control, the crab ends up living only to serve the sacculina and help her and her family infect other crabs.

Image courtesy Michael Rogalski



  1. I’ve known people in relationships like that. I think I’ll write a story about one and name one of the characters Sacculina.

  2. Great. That’s all we need, giant zombie crabs!

    … Ok, I gotta admit I am interested in seeing some videos of this freak of nature.

  3. Its like that wasp then lays its in eggs in other aphids, other insects, and occasionally small mammals. Turns them into zombies who take care of their incubating young, as those very same pupae devour the host from the inside. Existence is quite nasty in its ingenuity.

  4. “It won’t all be book promotion, though. Promise.”

    3 – 3 is pretty high in the self-promotion department…


    That post about S. coleoptrata isn’t in the book. There’s another non-booker coming up later today.

    I’m trying to do a couple book posts + at least one non-book thing each day.


    a) Joke.
    b) It is possible this situation makes the crab feel loved, but I doubt it.
    c) Joke.

  6. I do have to wonder–are Sacculina infested crabs cooked and served just like any other?

    I don’t eat crab, but even if I did, I don’t think I would anymore.

  7. Carl Zimmer’s excellent book Parasite Rex covers Sacculina as well as several other fascinating parasites.

  8. daneyul @ 23

    I thought the same thing. I don’t see why they wouldn’t be unless they are easily recognized. Gross. So gross.

  9. If you think that is wild- check out the fungus Cordyceps….

    And imagine the whisper in your ear…. “climb. climb. climb”

  10. Rhizocephalan barnacles! You’re the first person outside my Parasitology class to know of them, and they’re weird enough that I can’t explain them without sounding like I’m making it up. They simultaneously horrify me and make me so happy.

    It’s the male larvae (male adults?) that really do it. Free-swimming penises, just looking for a female….

  11. Wow, that’s even creepier than the Tarantula Hawk, the state insect of New Mexico. It’s a beautiful wasp with an electric blue body & orange & black wings. They find a tarantula & sting it, which paralyzes it. Then the wasp drags the helpless tarantula to its hole in the ground & lays an egg in the spider’s body. When the larva hatches, it feeds on the tarantula, which is still alive. Intelligent design my ass.

  12. I was going to recommend that people who found this interesting should read Parasite Rex but then saw that someone else had already made that comment so I’m just going to repeat that.

    And now we just need a parasite that makes zombie unicorns…

  13. #23, I’ve seen green crabs with advanced infections, and the parasite is unmistakable; I can’t imagine anyone opening up an infected crab and NOT realizing that something was off.

    Maggie Koerth-Baker, my second favourite parasite is a local tapeworm called Ligula intestinalis. Its primary host- the host that carries the adult tapeworm- is a bird, and the intermediate host- the “stepping stone” that carries one of the larval stages- is a fish. The bird acquires Ligula by eating infected fish. Seems simple enough, but the parasite makes things easier for itself by making the fish swim upside down- this disrupts the camouflage of the fish, and the fish’s white belly attracts the attention of the bird.

    My favourite parasite is Dracunculus, mostly because of its awesome name.

  14. the way people carry on, it almost makes it sound like being hijacked by a brain-parasite was a bad thing… Fess up now, how many of you have actually tried it? hmmm?

  15. my all time favorite fish to open up and marvel at the sheer number of gut parasites in is the common spiny pufferfish in Japan. Amiable,slow moving, take your hook ten times in a row (the same fish) and almost completely useless.

  16. Nice Takuan!!

    For sheer numbers of parasites, my fave fish is the sea raven. Not only does it growl at you when you pick it up, you can often see knots of roundworms bulging just beneath its skin.

    I do this for a living, and I love my job.

  17. “The disease then enters a neurological phase when the parasite passes through the blood-brain barrier. The symptoms of the second phase give the disease its name; besides confusion and reduced coordination, the sleep cycle is disturbed with bouts of fatigue punctuated with manic periods progressing to daytime slumber and night-time insomnia.”

    that sounds disturbingly familiar

  18. Maggie, Xenie likes you. You friend. Try to remember yourself before you knew anything. Then trust your old self more in her knowing. Sharing on a blog can be brutal if you read the posts. Icky stuff . Never take a digital post personally. That is the first law of cyber space. Globally.

  19. #44 I am convinced that you are massively intelligent. You proved it to me many times over. Any disease of the brain that turns you into a blithering idiot should be opposed. Normal life should be looked at as a possible cause. Perhaps we are only different in the nature of our parasites and drugs I wonder?

  20. @30 GHEDE

    Toxoplasma gondii doesn’t just change rat behavior.

    If, like half the population, you’re a human infected with T. gondii, you’re about twice as likely to die in a traffic accident. That’s the same increased risk as having a blood alcohol level of 0.06. Infection has also been associated with schizophrenia.

  21. I still don’t understand the “either/or” paradigm of agnostic scientists. ESPECIALLY scientists- as ones who study energy and its dynamics.
    I get that scientific discoveries counter most Biblical claims and ideologies. But that’s just organized religion, which is extremely limiting to growth in any direction. What about the possibilities of a grand universal force that is outside of limited explanation.
    It just seems to me that the universe is much grander and amazing than we can comprehend, and I would think that the more open minded and deeper you explore into science, the more mysterious and magical your perspective of it becomes. I understand writing off an outdated, dogmatic deity, but to write off ALL concepts of a higher mind or energy by scientists seems to be itself limiting, small minded, and stunting our evolution just as much as these flocks of mindless, religious sheep.
    If we never looked into a microscope or telescope, imagine how ignorant and scientifically stunted we would be now. I think the same case could be made for not looking into the mind, the aether-4th dimensional realm, etc.,etc.
    Not to be so serious and stuff,it IS a great article:)

  22. @48
    I’ve found that studying science does indeed make the natural world seem more magical and mysterious. The more you study any complex subject (in my case, molecular biology), the more you learn to think of even more questions that we don’t know the answers to yet. It’s a really humbling experience.

    But this doesn’t lead me (or many of my colleagues, AFAIK) to religion. Because so much of science is about looking at complex systems and finding that there’s an unintuitively simple, mechanistic explanation for it. So when we see some new, wonderful and fascinating phenomenon all of our experience tells us that there’s going to be an elegantly simple explanation, if only we can find it.

    Er, the tl;dr version:
    We don’t turn to God to explain the mysteries of the universe because we’re used to finding that mysteries usually have pretty simple answers. This doesn’t mean that God doesn’t exist, it just suggests that he doesn’t need to exist as an explanation for all this cool stuff we see.

    RE “looking into the mind, the aether-4th dimensional realm, etc.,etc. ”
    If you can come up with a hypothesis and a way to test it, then congratulations – you’re doing science! The mind is the subject of enormous and intense study, as are further dimensions.

    If there’s something that scientist aren’t looking in to, it’s because no-one can think of an interesting and objectively testable question. It’s all very well hand-waving and making impressive statements about aether, but until you can nail down exactly what you mean and use that to make a testable prediction, the scientific method can’t help you.

  23. Funny, all I could think of when I read this was, “Huh, sounds like my ex-wife”.

    Sorry, I know it’s trite and all, but, well, it’s also true, so I couldn’t help myself.

  24. @49
    That sounds good. That’s my feeling as well.
    But I WAS saying that I agree science leads us to paradigms beyond religion. (I personally despise anything that keeps expansion of thought and experience stunted in any way-I’m more of a fan of ERIS than that control freak King James)
    And I agree that things like 4th (or higher) dimensional study and such is difficult without better understanding of said realms. It seems very difficult especially dealing with things outside of our experience – things that are almost impossible to nail down or make a testable prediction with current models.
    The atom bomb or micro-processor couldn’t have been created 500 years ago because it was outside of the models and thinking of that time. I guess we’re just S.O.L. until discovery plods along to new hights and perspectives of our universe as time goes by.

  25. Maybe people can also be infected with a currently unknown parasite that causes us to exihibit and persue greed, ego, religion, love…

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