The gut contents of a brown trout (Salmo trutta) included horsehair worms (Gordius robustus, Nematomorpha: Gordiida) emerging from a camel cricket (Ceuthophilus sp., Orthoptera: Gryllacrididae). This provides more evidence of secondary ingestion than most previous reports of predation on horsehair worms, but it also illustrates the difficulty of distinguishing in practice between direct and secondary predation.
Cochran, Philip A.
"Secondary Predation on the Horsehair Worm Gordius Robustus (Nematomorpha: Gordiida),"
The Great Lakes Entomologist, vol 40
Available at: https://scholar.valpo.edu/tgle/vol40/iss1/9