Field observations revealed cases of predation on horsehair worms by brown
trout (Salmo trutta) in Maryland and Minnesota a rock bass (Ambloplites rup
estris) in Kentucky, and a crayfish in Wisconsin. Some fish contained more
than one worm and may have consumed reproductive aggregations. In laborator
y feeding trials with Gordius robustus, most individuals of several fish sp
ecies either ignored the horsehair worms or rejected them after taking them
into their mouths briefly, but a green sunfish (Lepomis cyanellus) consume
d both individual worms and a compact ball of 18 worms. A literature review
yielded cases of predation on horsehair worms by at least 12 fish species.
Horsehair worms usually were only a trace component of the diet, but some
individual fish had eaten multiple worms.