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  • José H. Leal

Zombie Snails!


In the past few days, the online media has been abuzz with a renewed appreciation for the strange parasitism of the worm known as Green-banded Broodsac (Leucochloridium paradoxum) on European Amber Snails (genus Succinea). Green-banded Broodsacs invade eyestalks (also known as tentacles) of snails after growing inside the victims’ bodies. Often, both eyestalks become occupied. Once inside the eyestalk, a worm starts a “dance,” pulsating back and forth. The worms' motion and color pattern make it look like caterpillars sticking out of the snail’s head. Caterpillars are a favorite food for birds, and the acidic environment of birds’ guts are favorable to worm development and breeding. The worms apparently are capable of directing the snails onto open areas, where their caterpillar-like eyestalks are easily spotted by the birds. Eventually worm eggs will come out in bird feces, only to be eaten by a healthy snail, and the cycle is thus completed. Click here to see a clip of the parasitized snail and read more about this odd zoological pairing in Wired.


Green-banded Broodsac Worms (Leucochloridium paradoxum) infesting Amber Snail (Succinea species). Photo copyright Stas & Lana, CC-BY-NC-4.0, as posted in iNaturalist.