Adult males and females live in the intestine of waterfowl and aquatic mammals. Females release embryonated eggs which pass in the feces and are eaten by amphipods. Within the amphipod an acanthor hatches from the egg and uses its hooks to penetrate into the hemocoele of this intermediate host. The parasite develops into an acanthella and then a cystacanth.
The presence of a cystacanth alters the behavior of the amphipod, depending upon the particular species of Polymorphus involved. These behavioral changes make the amphipod more susceptible to predation by the definitive host, and also affect mate choice by infected amphipods.