Description: 

This parasite makes male crabs think that they’re pregnant females. 

Transcription: 

Most of us know barnacles as those small, shelled creatures you find at the beach 

attached to rocks and piers. But, there’s one species of barnacle with a very 

different sort of life cycle. It’s a parasite that castrates crabs and turns them into 

barnacle baby-making machines. I’m Anna Rothschild, and this is Gross Science.

So this parasitic barnacle is called Loxothylacus panopaei, and it starts out its life 

just like most barnacles do—as a free-swimming creature looking for a home.

And, home for this particular parasite is inside of a mud crab. When a young female

barnacle finds a mud crab (and let’s say it’s a male mud crab, though they infect 

females as well) she undergoes a transformation, losing her eyes and legs. 

Then, she injects herself into the crab’s circulatory system. Once inside she starts

forming a root system throughout the crab’s body, castrating him in the process. 

Soon, a sac starts poking out from the crab’s abdomen. This is an “externa,”

the reproductive organs of the adult female barnacle. The externa attracts male

barnacles, and when a male arrives he injects his own cells into the sac, 

which grow into a testicle-like structure. In fact, the adult male barnacle exists 

only as a testicle, fertilizing the female barnacle’s eggs. 

Questions: 

1. What are barnicles? 

2. What kind of parasites do male mad crabs have?

3. Discuss the life cycle of these parasitic barnacles.