horsehair worm; gordian worm; hair worm
Refers to any worm of the class Gordioidea; often found in water or as parasites in insects.
See also: 線形虫
I found a horsehair worm in the river.
wireworm
Specifically the larva of a click beetle; an agricultural pest that damages roots and tubers.
See also: コメツキムシ
The potatoes in the field had wireworms.