Now for something that will be enough to give anyone nightmares. No one likes the idea of parasites, right? Tiny organisms living within bodies many times bigger than them, doing their own thing is enough to give people the shivers. Well, parasites can do much, much worse than just living inside of another animal.
The parasite in question: the green-banded broodsac, or Leucochloridium paradoxum, is a flatworm typically found in Europe and North America, which has two hosts: snails and birds. This parasite alters the behavior of snails, effectively turning them into zombies.
It all begins when the snail accidentally eats the tiny flatworm, whilst grazing on leaves. The parasite then travels to its stomach, and swells up into huge ‘broodsacs’, which invade the tentacles of the snails, turning them into thick, colorful, and pulsating tubes (as seen below).
This brilliant transformation makes the tentacles closely resemble a caterpillar, which is not good news for the snail. This change to the tentacles messes up the snail even further: they stop finding safe, dark places to hide, and in doing so, make themselves more conspicuous.
Even worse news. Birds love caterpillars, and do not pass up an opportunity to snatch one. Forcing the host to resemble the prey of another species is called ‘aggressive mimicry’, and rightly so. After being eaten, the parasite can reproduce within the bird’s digestive system, as the bird is its definitive host. Once the flatworm has reproduced it exits the bird in its feces, and is picked up again by an unassuming snail. Then the nightmarish cycle starts over.
This messed up life cycle seems too ingenious to even be real — the process is so finely tuned and precise that it even alters the behavior of the snail to help things along, turning the snail into a real-life zombie!
Watch the cycle in the video below:
Hopefully a parasite like this will never transmit to humans, although there is one that affects ants, and it is absolutely brutal.