Leucochloridium invades a snail’s eyestalks

The worm then mind-controls its host out into the open for hungry birds to pluck out its eyes. The worm breeds in the bird’s guts, releasing its eggs in the bird’s feces, which are happily eaten up by another snail to complete the whole bizarre life cycle.

The worm, though, has a problem: Snails are largely nocturnal, and passerine birds, which hunt by sight, most certainly are not. So once the Leucochloridium has sufficiently developed in the eyestalk, it begins manipulating the behavior of its host, forcing it out into the many dangers of the light of day, where predators swarm and the sun rapidly desiccates. It’s probably using chemicals, but how it’s able to pull off this incredible feat remains a mystery, as do the chemical secrets of any number of other zombifying parasites (though scientists are making progress in decoding the compounds that the Ophiocordyceps fungus uses to assume control over ants).

And when the reckoning comes, the snail ends up with its eyes plucked out. But because birds don’t typically go after snails—only when their eyeballs look like caterpillars—they’ll take off without eating the rest of the body. (If the eyestalk happens to rupture on its own, the faux caterpillar will spill out onto a leaf and pulsate for some time before drying out. The worms really, really want to get eaten.) Mercifully, or perhaps horrifically, the snail will not only survive, but will regenerate the lost tentacles and eyespots and regain the ability to reproduce. That’s actually quite beneficial for these parasites, for the wounded snail eventually becomes another potential host capable of producing many more potential hosts.

https://www.wired.com/2014/09/absurd-creature-of-the-week-disco-worm/