boop

I just looked it up—it injects itself into the crab's body and replaces the crab's genitals with itself, grows roots into the crab's organs (including its brain), and controls the crab's behaviors so the crab will take care of the Sacculina larvae as a female crab would its own babies—if the crab is male, the Sacculina parasite will make the crab's body produce female hormones to basically change it to female.

Parasitism is wild because it ranges from organisms that are using another organism's resources but have a very minimal negative effect and for the most part are just hanging out, to stuff like this where the parasite is basically piloting the host's body like a mech suit.

The fun thing about it is that symbiosis exists on a kind of spectrum between parasitism and mutualism, and sometimes organisms can switch between parasitism, commensalism and mutualism throughout their evolutionary history and even individually depending on an organism's situation.

But I think it's usually at the extreme ends of the spectrum where you see these freaky levels of codependency where organisms become unrecognizable in the process of merging together.

unnamed malaise. sequel to this devil's minion true crime radio show AU piece