Duck flea

Swimmer's itch isn't just caused by ducks! Known as trematodes, the parasites responsible for this illness are found in the form of swimming larvae called cercariae. The parasite requires two hosts in order to develop. The first is the duck, while the second intermediate host is a freshwater snail from the gastropod family, called a limnea. The parasite cannot survive on its own without any of these hosts. Humans are merely an accidental host in this complex cycle. Before dying, the parasite causes a mild but unpleasant skin reaction. Taking a shower just after swimming reduces the risk.