February 20, 2020

5 Parasites Parasitic Organisms Found In Or On Crabs – Being Impregnated By Parasites

I absolutely love crabs, and though I don’t eat seafood 🍤 often because of mercury, I do love to order snow crab legs and steamed crabs with old bay, butter, and lemon on special occasions! I make sure that when I do eat crabs, that they look fully cooked. Generally, I have found the restaurants that I ate at to be pretty good about cooking snow crab legs fully, but not all restaurants fully cook their crabs.

When crabs are not fully cooked, you can end up eating the parasites and worms that live in them, which can make you sick. After all, crabs, like all living things, are also negatively affected by parasites. Some of these parasites can harm humans also when we eat raw or undercooked crabs. Other parasites found in or on crabs can harm them and even greatly reduce their numbers. So today, I will teach you about 5 parasitic organisms that affect crabs.

Parasites/Worms Found In Crabs

Paragonimiasis From Lung Flukes

“Paragonimus infection…can be very serious if the fluke travels to the central nervous system, where it can cause symptoms of meningitis” (“Paragonimus FAQs”, CDC).

Lung flukes are a type of flat worm that are found in raw and undercooked crabs and crawfish that tend to take up residence in the lungs. Lung flukes can cause any number of problems from breathing problems, coughing, typical symptoms of food borne illness (diarrhea, fever, dizziness, tiredness, etc), to coughing up blood.

“People get lung fluke infections when they swallow cysts containing immature flukes (larvae) in raw, undercooked, or pickled freshwater crabs or crayfish” (“Fluke Infections of the Lungs”, Richard Pearson, Merck Manual). 


Vibrio is found in undercooked crabs and crawfish, but just about any undercooked or raw seafood can have it. Vibrio infections occur most often between May and October, when the bacteria is present in very large numbers. 

Vibrio is really the biggest concern when it comes to eating raw or undercooked crab, and the symptoms that accompany vibrio are common to food borne illness (diarrhea, nausea, headaches, fever, weight loss, chills, stomach pain, throwing up, etc).

There are two types of vibrio that you need to know about: “Vibrio cholerae (VC/aka cholera), a bacterium indigenous to fresh and brackish water environments in tropical, subtropical and temperate areas worldwide, may infect crabs living in those environments. Vibrio parahaemolyticus (VP), another kind of bacterium, may be present in crabs living in estuaries and coastal waters” (“Food Safety Focus”, Centre for Food Safety).

Just last year in Maryland, there was an outbreak of vibrio, so the CDC had warned people to stay away from crabs for a while.

Read the full article here
Carcinonemertes Errans

This is a kind of crab STD, in the sense that they get it while mating. The male can give it to the female, and then the parasite can attach to the female and eat her eggs. 

“The parasitic worms spread from one crab to another during mating, and when they have established themselves on a female, they begin to eat her eggs. A female crab can carry up to two million eggs, and a worm will eat around 80 eggs during the two months she carries her eggs. It takes a lot of parasites to threaten the crab’s reproduction — but that is exactly what is thought to have happened in certain areas” (“Estuaries protect Dungeness crabs from deadly parasites”, 2015, University of Southern Denmark, Science Daily).

Loxothylacus Panopaei Aka Loxo

Image source: “File:Loxothylacus panopaei (I0266) (13048731864).jpg”, 2006, Smithsonian Environmental Research Center, Wikimedia Commons.

There is a barnacle that acts as a parasite that gets into the crab’s brain and takes it over. This allows the barnacle to control the crab’s body. This parasite called Loxo, then impregnates the crab, whether it is male or female, and then turns the crab into little more than a zombie with no control over its body. When the crab it invades is male, it turns it female so that it will raise and provide for its parasitic larva (babies).  Scary isn’t it?

“Loxo resembles a typical barnacle larva. A female larva infects a recently molted crab by burying into its shell. Once inside, she undergoes a series of changes and assumes control over the host crab, dictating major functions such as molting and reproduction…(she) eliminates the crab’s ability to reproduce, resulting in the crab instead caring for the developing larvae of the parasite…Loxo also compromises the crab’s immune system. Infection endangers both present and future generations of the mud crab” (“Undersea parasite turns male mud crabs female”, 2012, Marine Science, Science & Nature, Smithsonian Insider). 

 Briarosaccus Barnacles

Not all barnacles are parasites, but these, like Loxo, are parasitic. These barnacles do the same thing as Loxo; they impregnate the crabs. These impregnate king crabs, and then they make them raise and provide for their larva. 

“Barnacles are marine animals with outer shells, related to crabs and lobsters. Typically, they live on rocks or the sides of boats, filtering food from the water. However, Briarosaccus barnacles infect king crabs, turning them into zombies that raise and nurture the parasite’s eggs. The parasite basically takes over the crab’s brain” (“Zombie-generating crab parasites pose intriguing mysteries”, 2016, Lauren Frisch, UAF University of Alaska Fairbanks).

How To Fully Cook Crabs

Photo by Chait Goli from Pexels

Since crabs contain parasites, some of which are harmful to us, it is important that we cook all crabs thoroughly. If the crab is already dead, you can cook it more thoroughly by breaking up the limbs/legs first and then separating them from the body so that the heat can get inside of the crab and help kill some of the parasites inside of it. If the crab is still alive, then you can boil it for a while, then take it out after it is dead, and then remove the limbs and allow them to sit in the hot water and cook longer.

It is recommended to cook crabs at a minimum temperature of 350 degrees in the oven, or 154 degrees if you are going to boil it on a stove. You should cook crabs for around ten minutes at least. 


Photo by icon0.com from Pexels

Crabs can be great to eat on special occasions or holidays, but make sure that you are eating crabs that are well done and fully cooked, so that you are less likely to get sick from them. Also, if the seafood has a bad smell, then it is likely not fresh, so you should not eat it. 

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