Invasion of the Body Snatchers

A barnacle named Sacculina wants to nest inside a crab. A female Sacculina will look for a place to enter the crab’s body. When it does, it will leave its shell behind, not needing it anymore as it has the crab! Inside, Sacculina sets up shop, growing tendrils through the crab’s body and slowly feeding on it. It castrates the crab (if male) and effectively turns the crab into a female nanny for its young. This makes the crab not only infertile but also uninterested in mating. The barnacle, on the other hand, bores a hole open in the crab’s shell big enough to let male Sacculina in to mate. The zombie crab treats the Sacculina eggs and larvae as its own, having lost the will to do anything but serve its parasite master. Image credit: Hans Hillewaert.