Eggs of Leucochloridium paradoxum present in bird droppings hatch and penetrate through the skin of a succineid snail (Succinea spp., Oxyloma spp., and Catinella spp.) (1). The larvae migrate to the tentacles and form a broodsac. The parasite causes the snail to seek out bright areas, like the tops of leaves, where the parasite might be more visible (2). The large size, bright colours, and pulsating movement of the broodsac attempt to catch the attention of birds that normally feed on insects (3). When a bird eats the broodsac out of the snail’s tentacle (or sometimes the entire snail) the larvae are released into the bird’s digestive tract where they mature into adult tapeworms. The adults produce eggs that get released with the bird’s feces. L. paradoxum is found in wet marshlands throughout Europe (1) and in Japan (4). It is able to infect a wide variety of birds (1), which may aid in its dispersal.
Free-swimming, juvenile Cymothoa exigua males attach to the gills of a fish host (5). Upon reaching a critical size, a single male turns into a female and moves to the mouth of the fish (5). It cuts off the blood supply to the tongue, which eventually falls off. The female then takes the place of the tongue. Males are sometimes found with the female (6), suggesting mating occurs in the mouth of the host. Females keep the fertilized eggs in their body for early development before they are released. Females release a single brood (480 - 720 eggs per female) and die (6). Only one female is ever found per fish host, suggesting that the presence of a female prevents other males from turning female (6). C. exigua is known to infect snapper fish including Lutjanus peru and L. guttatus (6) and is found in both the Atlantic and Pacific coasts of North America (5).
Parasite Comics Team:
Dr. Chenhua Li (Lead, Ideas), Dr. Þórey Jónsdóttir (Illustrator, Ideas), Stephen Pollo (Writer, Researcher), Yuanzhe Wang (Digital Consultant).