Unlike most barnacles that are happy to simply stick themselves to a rock and filter food from the water, Sacculina and its kin have evolved to be parasitic, and they are horrifyingly good at it.
Alien species become invasive when their introduction to an ecosystem ends up causing ecological disruption in their new home.
This fame might make it seem there is just one fungus that can create such a nightmare. But in fact there are many species of them, and zombifying ants is not their only speciality.
Hornets put fear into the minds of most, but there is a parasite that the hornets fear (if indeed they are capable of fear).