Maccaffertium terminatum Mayfly NymphView 1 PicturesThis is a subspecies (Subspecies: Entomologists sometimes further divide a species into distinct groups called subspecies, which have two lower-case words on the end of their scientific name instead of one. The latter is the sub-species name. For example, Maccaffertium mexicanum mexicanum and Maccaffertium mexicanum integrum are two different subspecies of Maccaffertium mexicanum.) M. terminatum terminatum, formerly called Stenonema. Found mostly in larger rivers in western Montana. This is an immature nymph.
Kathroperla perdita (Sallfly) Stonefly NymphView 1 PicturesThis species is uncommonly collected except from wells. It is a hyporheic species living in the river gravels of river floodplains until it is ready to emerge.
The head shape is an important identifier.