Eustrongylides ignotus is an extremely pathogenic nematode which lives in the wall of the stomach (proventriculus) of herons and egrets and has caused die-offs in nesting colonies of some birds. Its bright color has earned it the nickname of “the big red worm.” The life cycle involves oligochaetes as the first intermediate host and various fish as the infective intermediate host. If the small fish are ingested by larger fish, reptiles, or amphibians, these can act as transport hosts. The color in this larval worm in a mosquitofish has been bleached out by the preservative. If straightened out, it would be longer than the fish.
Contributed by Mike Kinsella.