A strange snail was seen crawling on a hill in Taiwan, it was no longer alive but still wandered around like a real zombie, a zombie snail.
Imagine that one day a little snail finds tender leaves and eats them as it always does.
The snail, however, does not know that on those leaves there are also particular bird droppings: there are some eggs of Leukocloride.
The ingested egg develops, inside the snail, in what is known as sporocysts, a pile of whitish tissue that grows like a tumour.
Having no mouth, like many parasite worms, it remains there to absorb the snail’s nutrients.
As if that weren’t enough, Leukocloridium castrates its host so that the energy normally spent to produce eggs and sperm (snails are hermaphrodite) goes instead to support the worm.
When it is ready, the sporocyst sends out branches that dig through the snail’s body and into its eyes where it forms a brood bag full of larvae.
Now the larvae start controlling the mind and begin to pulsate in the snail’s eyes to imitate a caterpillar.
A hungry bird flying over there sees what looks like a caterpillar, approaches, tears out the snail’s eyes and devours them.
The worm reproduces in the bowels of the bird, releasing its eggs into the bird’s faeces, which will be devoured by another snail to complete the entire bizarre life cycle.
The Zombie Snail
The snail in question is the Succinea or amber snail, a very normal snail.
It only becomes a zombie after eating its tender leaves, finds bird droppings and eats them!
What this worm combines is really impressive: it changes the snail’s behaviour, controls it and pushes it into the sun. In the sun the snail will dehydrate.
This is because snails are mostly nocturnal, and passerine birds, which hunt on sight, are diurnal.
At the tip of the snail’s tentacle there is a rudimentary eye pot.
The snail cannot see the colour and the eye does not have the necessary muscles to concentrate.
But the snail has muscles that retract the tentacles, which it can then reposition by pumping them full of liquid.
Leukocloridium swells the tentacle to the point where the snail is no longer able to retract it. In this way the host is left with a massive “stroboscopic” eye that he can no longer hide.
Infected snails are up to three times more active than their non-zombified peers: they can cover a whole metre and a half in just 15 minutes.
Why does Leucochloridium lead the snail to commit this suicidal act?
Because in order to complete its reproductive cycle it must be located in the gastrointestinal tract of birds and finally transmitted to other snails through their faeces.
This is not a painless process for the snail. “It is very likely that it suffers, the molluscs have the necessary receptors to experience pleasure and pain and to secrete substances to relieve the sensation of pain”.