These are common parasites of aquatic birds and mammals. Adults live in the intestine and release unembryonated eggs which pass in the feces. Eggs hatch after a few weeks, releasing a miracidium. The short-lived miracidium swims about searching for a suitable snail, such as Helisoma spp. or Physa spp.
After the miracidium penetrates the snail it transforms into a mother sporocyst, which usually migrates to a site such as the heart. After several weeks it begins to produce mother rediae which migrate to the digestive gland or ovotestis of the snail and begin producing daughter rediae. The rediae feed on the tissues of the snail, and can castrate it by devouring the gonads. About 1 month after the initial infection, daughter rediae begin producing cercariae, and continue for the life of the snail.
The cercariae seek out either another snail, a leech, or a fish or tadpole as a second intermediate host. They penetrate the body surface or enter through an orifice, and then encyst as a metacercaria. They remain until eaten by a definitive host, and can retain infectivity for many months.