Data collected from an ecological study of the mayfly Potamanthus rnyops (Walsh) in Michigan showed intraspecific variability in taxonomic characteristics that have been employed by previous investigators for species separation. Nymphal dorsal maculation patterns varied considerably within a single population. Also, the ratio of mandibular tusk length to head length increased with successive nymphal instars. Certain adult taxonomic characteristics, particularly relative male imago eye size and distance of separation, were either too poorly defined or too variable to be conclusive in species identification.
Lord, Robert J. and Meier, Peter G.
"Intraspecific Variation in Taxonomic Characteristics of the Mayfly Potamanthus Myops (Walsh),"
The Great Lakes Entomologist, vol 10
Available at: https://scholar.valpo.edu/tgle/vol10/iss2/3