Thank Goodness the Hitchhiker Was Only an Oyster Pea Crab.

Oyster Pea Crab

Oyster Pea Crab

On Monday, my husband and I were over at his parents’ house and he got busy shucking some oysters a friend had dropped off — Eastern oysters, Crassostrea virginica. I was chatting with my father-in-law when my husband started hollering about something from the kitchen, something strange he’d found in the oyster he had just opened.

He comes over and shows us the shell, and there, perched right inside was a very round, very tiny, very translucent crab. Its innards were clearly visible, fluffy-looking red streaks, and we figured it was dead, since it was inside an oyster and the oysters had been in the fridge. We had quite the laugh, thinking about the silly thing crawling into an oyster at a moment when its shell was gaping open. But we were also totally puzzled: my father-in-law was convinced it was a blue crab; my husband thought it to be a fiddler; I had no earthly idea. So we put it into some tap water mixed with alcohol (gin, to be exact, since it was the nearest thing handy on the counter), reckoning that might “preserve” it since I said right away I wanted to take it to a local university to find out what it was.

A few minutes later, I held it up to a window to check it out more clearly. What it was doing, clearly, was moving — very slowly, very sluggishly, obviously dying but still alive nonetheless. So we put it back into fresh water in a small jar (…okay, so it was a pill bottle, since again, it was the nearest small container that was handy), and popped it into the fridge.

The next afternoon, we dropped it off at George Mason University’s biology office. I had to leave a note, since all the faculty were in a meeting, but the grad student at the desk was all, “Wow, cool. Oh, wow. Cool.”

I never expected such a fast reply, but an assistant professor e-mailed me that very evening:

The critter you found was an oyster pea crab (a full grown female). These are quite common, but can surprise the unsuspecting oyster consumer (as you discovered). They live most of their lives with the oyster in its shell. They feed on food particles filtered by the oyster and sometimes on the oyster itself.

Thanks for sharing it. We will make it part of the collection for our invertebrate zoology class.

Wow, indeed!

Chinese mitten crab

Chinese mitten crab

I was relieved that it was this kind of crab, unsettling as it was to find it inside an oyster, and not another species I’d come across in my Google crab research: the Chinese mitten crab (Eriocheir sinensis), so named for its furry pincers.

Though they’re non-native, it seems that they are not yet what you’d call widespread: as of February 2008, the Smithsonian’s Marine Invasions Research Lab had reported only 13 individuals captured from the Chesapeake Bay, along with a number of others along the coast in New Jersey, New York and in various places in the Great Lakes, where they are believed to have originated through release of ships’ ballast water there. But, according to the USGS, a lone female can lay up to 1 million eggs at one time:

Mitten crabs spend most of their time in fresh water but move to brackish water to reproduce (at least 26 ppt). Their primary food is aquatic vegetation, but will also feed on mollusks, fish, and other crabs. Mature adults are 38-50 mm in carapace width. A female can lay up to 1 million eggs in a one event. One effect of the mitten crab could be the collapse of support structures following successive years of mitten crab burrowing (Ingle, 1986). In the Far East, mitten crabs are an intermediate hosts of lungflukes, Paragonimus ringeri, which occur in humans (Ingle, 1986)

The USGS adds that where it has occurred in California, the mitten crab has become troublesome because of its tendency to congregate around water pumping facilities’ intake pipes.

One way to approach thinking about invasives–along with other elements of environmental change, whether or not you generally agree with it–is this: risk management. (Thanks to my brother for this idea; I read an old post of his several days ago that mentioned risk management.) What are the risks of non-native species introductions–to humans, to native flora and fauna, to infrastructure, to the economy?

I’ll wrap this up by saying that I was on my way to try and find an easy-to-summarize, negative economic example of invasives, but got sidetracked by what looks to be a really interesting news website: Sightline Daily.

23 responses to “Thank Goodness the Hitchhiker Was Only an Oyster Pea Crab.

  1. So is an Oyster Pea Crab an invasive?

  2. Michelle Donahue

    Not as far as I can tell — it’s one of those things that just kind of hangs out and goes unnoticed most of the time, but doesn’t do much, if I remember from what I read when I was researching the matter.

  3. I just found one in my oysters, too. Definitely, a scary experience when you don’t know what it is. I feel a little better now. Sort of feel sorry for the poor gal, so far from home now she’s in Kentucky.

    While doing research to find out what it was I found an article from 1913 in the NY Times – apparently, they were delicacies at one time! Ick! Not in my house.

    http://query.nytimes.com/mem/archive-free/pdf?_r=1res=9F07E5D6133FE633A2575AC0A9679D946296D6CF

    I’m a little scared to open the rest of the oysters having found two already! Maybe it’s time to go vegetarian again. :D

  4. are they safe to eat?

  5. Michelle Donahue

    i’m not certain. I didn’t come across anything that indicated they were unsafe to eat, but they’re pretty weird looking and that is probably enough to deter me from ever wanting to try munching on them. but who knows? if you’re an adventurous eater, i don’t think that a tiny crab could hurt too much.

  6. Today I tried my very first oyster ever in Georgetown….. and I found this same thing! How odd. I didn’t eat him though. My oysters were steamed so the little crab got steamed as well. He turned out to be more orange than the photo above.

  7. Michelle Donahue

    My mother-in-law apparently is very familiar with them, and says it’s good luck to eat them when you find them. I shudder!

  8. I’ve been seeing these in the oysters at my oyster bar. They are very facinating. Thanks for posting!

  9. Michelle Donahue

    wow, how weird! several GALLONS of oysters required to find a pint of these things! The language of this old NY Times recipe is pretty hilarious, too. Thanks so much for sharing. Where is your oyster bar, by the way?

  10. I loved the article, too! I enjoyed your post and have shared this with several guests in the restaurant. I’m at King’s Fish House in Corona, CA. Stop by when your are in the area.

  11. Michelle Donahue

    Next time I’m in California, sure! It might be a while though — I’m in Virginia.

  12. Pea crabs are awsome to eat-much sweeter than the oyster. They are good both cooked or raw. Yum-wud love to have a pint right now! They are typically found only in salty oysters in NC. We had a bushel today and it was full of crabs–a real bonus.

  13. Nora Chamberlain

    We found one of these crabs on March 10, 2012. We had purchased oysters in Old Lyme Ct and were shucking them for dinner. My daughter attends the University of Vermont and wanted to save the crab to bring up to her professor on Monday We live by the shore so we went down to the beach and put sea water and seaweed in a container. We put the crab in the water and it survived and was moving around actively. Is it possible for her to allow this crab to live for as long as it will with what she has set up as a habitat? What would she have to feed it? It is quite an interesting creature and she surely does not want to eat it. It really launched some great conversation!!!! catcrazy7@yahoo.com

  14. We just got a few oysters from Kroger locally and found a little pea crab too! Glad to have found this website to explain it.. wasn’t sure if the oyster is still safe to eat. Consider it eaten! Thanks!

  15. Was pretty shocked when I found one in a Blue Point from Whole Foods in NYC today, but down the hatch it went (after reading that 1913 nyt article). Added a nice little crunch.

  16. I was making oysters last weekend and I found several with these crabs in them, I thought they had gone bad and threw them out for the gulls…. now that I know they were a delicacy I am kicking myself for throwing them away so I am going back to that market to search once again

  17. We found one in a blue point from whole foods in MInneapolis MN today

  18. I had one at the Yorktown pub yesterday .fist time I’ve heard of them. but I ate it for good luck. I made sure not to taste it because it looked unusual. hope the lucky oyster story is true !

  19. Whoa! Just opened six Blue Points, first one had a crab, then another was found. Purchased @ Harbor Fish Portland ME. That creeped me out, so google I did. Thank God it’s not a bad thing. Thanks for your comments…phew.

  20. Turned up two full grown femalesin a dozen blue points from Norwalk, Ct and was reluctant to eat the oysters, but got over it . Since these little guys are commensal where they do no harm to their host, or an actual parasite?
    As I have never seen them before and found two in one day, I am also wondering if they have increased as a few folks also mentioned blue point oysters as home to these crabs? Any oyster fishers out there who can enlighten us?

  21. Preston from Wisconsin

    I just found one of these little crabs in my greenshell Mussels from New Zealand, apparantly there are several names for these small crabs depending on which host they are from, but are all from the pea crab family. The moment I saw it I wanted to eat it, so figuring most crustaceans are edible, I scarfed it down. Yummy crunchy little legs and shell gushing with flavor! I wish I could find more, or just eat a bowl full of the little buggers!

  22. My 8-year-old son just nearly sucked one of an oyster shell. What a surprise indeed. I was really hoping it wasn’t a clot of worms in there after I saw the wiggling legs.

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