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Body snatching parasite creates crab zombies

Posted at 11:33 PM, Mar 31, 2016

It sounds like a plot straight out of a science fiction movie; an alien parasite takes over a body without detection. That parasite takes control and then lays eggs in them. Now the creature spends all of its energy taking care of these invasive babies so they can hatch millions over and over.     

But it's not a plot for a new science fiction movie, it's the reality taking place every day in the Chesapeake Bay. 

Biologist Carolyn Tepolt said the parasitic barnacle called Loxothylacus panopaei or Loxo for short, is called a body snatching parasite. Tepolt and fellow biologist Monaca Noble are studying them.

This parasite was first introduced into our bay in the 1960's when oysters were transplanted here from the gulf. The parasitic barnacle moved right in and started to infect our local mud crabs. There are millions of the fingernail sized mud crabs in the bay and tributaries.

"Lot of things eat them, birds, fish, other crabs, all sorts of things," Tepolt said. "So they are a pretty important part of the bay's ecosystem, even though you may not have actually seen one."

Scientists at the Smithsonian Environmental Research Center have been studying the effects of these "body snatching" parasites on mud crabs for more than a dozen years. 

Noble is gathering mud crab samples from the Rhode River near Edgewater. These crabs to the lab to see what the Loxo parasite does.The parasite will attach itself to a crab and then insert tiny threads that go throughout the entire crab body.

Then the parasite castrates the crab, which is just the beginning of the transformation.

"And the parasite actually changes the crab's behavior so it feminizes the male crab," Tepolt said. "They'll start to look and act like female crabs so their aprons will broaden out and look female. They'll exhibit maternal behavior toward the parasite."

When the crab is infected, the male parasite fertilizes the eggs and the crab is controlled by the loxo parasite to take care of the egg sack. 

"That's part of why they got the name body snatcher because they are really taking over their crab host," Tepolt said. "Taking the crab out of the gene pool, hence the name Zombie Crab. The crabs are still alive, they're still walking around but they're basically just carrying around the parasite, a vehicle for the parasite to move around and reproduce."

After the crab, unbeknownst to him, has given birth over and over, they die. 

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