Schistocephalus solidus is a tapeworm of fish, fish-eating birds and rodents. This hermaphroditic parasite belongs to the Eucestoda subclass, of class Cestoda. It parasitizes fish and fish-eating water birds. The fish-eating water bird is the definitive host and reproduction occurs in the bird's intestine. Eggs of the tapeworm are passed with the bird’s feces and hatch in the water where the first larval stage, the coracidium, is produced. The coracidium is then ingested by the first intermediate host, a cyclopoid copepod (e.g. Macrocyclops albidus). The second larval stage then subsequently develops in the tissue of this host. Within one to two weeks, the infected copepod is ingested by the second intermediate host, the three-spined stickleback, Gasterosteus aculeatus. The third larval st