Large Amber Snail

• It is the host of the fluke Leucochloridium paradoxum, whose larvae invade the snail's tentacles and turn them into two green and red swellings that pulse like caterpillars so that birds will eat them and complete the parasite's cycle.
• The parasitised snail changes its behaviour: instead of hiding, it exposes itself on sunlit leaves, where birds spot it easily.
• This is the zombie snail, and its story is among the most cited in parasitology. The trematode Leucochloridium paradoxum infects it and colonises its tentacles, forming swollen sacs with green and brown bands that pulse rhythmically and mimic a caterpillar.
• And it does not stop there: the parasite manipulates the snail's behaviour. Infected snails abandon the shade, climb to the high, exposed parts of the vegetation and come out into full daylight — precisely the opposite of what a healthy snail would do.
• The target is a bird. The bird sees the pulsating tentacles, mistakes them for caterpillars and eats them, and the parasite completes its cycle in the bird's gut, from where its eggs pass out with the droppings and go on to infect more snails.
• The snail usually survives and regenerates its tentacles, which allows the parasite to repeat the operation.
• Its shell is thin, translucent and amber-coloured — hence its name.
• Despite living at the water's edge, it is a terrestrial pulmonate snail, not an aquatic one.

Skeleton type

Invertebrate - external calcareous shell (mollusc)

Habitat & environment

Marsh vegetation on riverbanks, marshes and waterlogged meadows

Sources consulted: Wesołowska y Wesołowski (2014), Journal of Zoology; Lewis, trabajos sobre Leucochloridium; Fauna Europaea