The green-banded broodsac, known scientifically as Leucochloridium paradoxum, is a parasitic flatworm with one of the most astonishingly complex life cycles in the animal kingdom. To complete its developmental cycle, the parasite must travel from its intermediate host, the land snail Succinea, to its definitive host, songbirds. Once the flatworm larva enters the snail, it consumes the host's digestive system and forms a specialized structure called a sporocyst.
This sporocyst branches throughout the snail's body and invades its eyestalks. There, the broodsac inflates and begins to pulsate rapidly with vibrant bands of green, white, yellow, and brown, perfectly mimicking a wriggling caterpillar. To maximize visibility, Leucochloridium paradoxum alters the behavior of its host through neurochemical manipulation.
While normal land snails instinctively seek dark, humid shelter to avoid predators, infected snails lose their negative phototaxis. The zombie-like host climbs upward onto exposed vegetation and sunlight, displaying its swollen, rhythmically throbbing tentacles to airborne predators. Birds mistake the pulsating eyestalks for caterpillars and pluck them off, ingesting the parasite's larvae.
Inside the bird's digestive tract, the flatworm reaches sexual maturity, reproduces, and sheds eggs in the avian droppings, which are later consumed by new snails, repeating the gruesome, hypnotic cycle of biological mind control.