Leucochloridium paradoxum is a parasitic flatworm that uses gastropods as intermediate host. The worm in its larval, miracidia stage, travels into the digestive system to develop into the next stage, cercariae. The cercariae growzinto long tubes, called sporocyste extend to form swollen "broodsacs" filled with tens to hundreds of cercariae. These broodsacs invade the snail's tentacles (preferring the left, when available), causing a brilliant transformation of the tentacles into a swollen, pulsating, colorful display that mimics the appearance of a caterpillar or grub. The broodsacs seem to pulsate in response to light intensity, and in total darkness do not pulse at all (1). The infection of the tentacles of the eyes seems to inhibit the perception of light intensity. Whereas uninfected snails seek dark areas to prevent predation, infected snails have a deficit in light detection, and are more likely to become exposed to predators, such as birds. Birds are the final hosts where the cercariae develop into adult distomes in the digestive system of the bird. These adult forms sexually reproduce and lay eggs that are released from the host via the bird's excretory system. These droppings are then consumed by snails to complete the life cycle of this parasitic worm.
The resulting behavior of the flatworm is a case of aggressive mimicry where the parasite vaguely resembles the food of the host, using this as a ticket into its body. Contrast this with other cases of aggressive mimicry, where only a part of the host resembles the target's prey, and the mimic itself then eats the duped animal.
1) Notes on the Life History of Leucochloridium fuscostriatum n. sp. provis. (Trematoda: Brachylaemidae) Edwin J. Robinson, Jr. The Journal of Parasitology, Vol. 33, No. 6, Section 1 (Dec., 1947), pp. 467-475 doi:10.2307/3273326
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