These are the largest stoneflies in Ohio (up to 2.5 cm). The common name is Salmonfly but Giant Stonefly is also commonly used. There are two or three species in the family Pteronarcyidae in Ohio, Pteronarcys dorsata (Say) is the most prevalent of the three, albeit quite rare itself. P. dorsata is indistinguishable as the nymph from P. pictetii Hagen, but presence of the latter is questionable. In their recent review, DeWalt, et al (2012) don't include it in their lists, but Stewart & Stark (2002) list it for Ohio. Gaufin (1956) states that P. pictetii as "reported for Ohio by Needham and Claassen (1925) [no county given]" but checking Needham and Claassen (1925), P. pictetii is listed under P. nobilis [now an outdated name] with a wide range that would include Ohio. At best, it has not been collected in Ohio since 1925.

Pteronarcys dorsata is listed in DeWalt, et al. (2012) as found in Columbiana Co. Ohio EPA reports 63 specimens found in 14 streams (Bolton, 2010). It has been reported in the Clear Fork of the Mohican (Ashland Co.) by several citizen scientists, David Spreng, Jon Horn, Jon Bossley and Don Dean; and, recently in the Kokosing R. (Knox Co.) by Robert Davis and Don Dean.

The other species, Pteronarcys cf. biloba has been putitively identified in Ashtabula County by the Ohio EPA in their routine water samples (Bolton, 2010) from a single nymph. This would be the westernmost extention of its range and rare in Ohio. It was also reported in Lake Co. by Martin Tkac in his doctoral thesis (Tkac, 1979) as Allonarcys biloba [an outdated synonym for Pteronarcys biloba] from one male and one female nymph.

The species of Pteronarcys can be distinguished from other stoneflies by their size, dark color and the fact that they have branched gills on the 2 abdominal segments nearest to the legs, as well at the base of the legs. P. biloba has horn-like protrusions on the sides of the abdomen, whereas P. dorsata lacks these protrusions.

These stoneflies are shredders and breakdown leaves. They are found in and near leaf packs in rapids of cold water streams. The nymphs reach their largest size in May just prior to eclosion as adults

Pteronarcys biloba

Pteronarcys dorsata