Fishfly larvae look a lot like hellgrammites but usually do not grow quite so large. Unlike hellgrammites, they lack gill tufts below the abdomen, and the abdomen tip is forked, with 2 short, fleshy tails, and each tail has a pair of hooks. They are generally fairly light-colored; often tan with a reddish cast.
Like the larvae of dobsonflies and alderflies, fishflies have 3 pairs of jointed legs in the upper part of the body, with each leg tipped with a tiny, 2-parted pincer; they have several fleshy filaments extending from the sides of the abdomen; and the mouthparts are large pincers.
Take care if handling fishfly larvae; they can pinch you with their stout mouthparts. Either hold them just behind the head, or use forceps to handle them.
Similar species: Hellgrammites (larval dobsonflies) are usually dark brown or black, usually larger, and have 8 pairs of pointed, leglike appendages along the abdomen, each with a cottony or hairy gill tuft as the base. There is a pair of hooked, leglike appendages at the hind tip — not a pair of fleshy tails. Alderfly larvae have 7 pairs of pointed, leglike appendages along the abdomen; although, like fishflies, they lack external abdominal gill tufts, they have only a single tail extension. The larvae of some aquatic beetles also have fleshy filaments along the abdomen and/or 4 hooks at the hind end. However, those that have 4 hooks have all of them arising from the same extension, not 2 hooks each from 2 extensions.