Snail infected with flatform (Leucochloridium paradoxum)

"Leucochloridium paradoxum", the green-banded broodsac, is a parasitic flatworm. Its intermediate hosts are land snails, usually of the genus "Succinea". The pulsating, green broodsacs fill the eye stalks of the snail, thereby attracting predation by birds, the primary host. These broodsacs visually imitate caterpillars, a prey of birds. The adult parasite lives in the bird's cloaca, releasing its eggs into the faeces.