Formica rufa subsp. difficilis Emery, 1893k: 651, pl. 22, figs. 9, 14 (w.q.m.) U.S.A. (Virginia). Nearctic.

Primary type information: Primary type material: syntype workers, syntype queens, syntype males (numbers not stated). Primary type localities: U.S.A.: Virginia (T. Pergande) (invalid restriction of type locality by Wheeler, 1913i: 478; no lectotype designated), U.S.A.: New Jersey (T. Pergande) (invalid restriction of type locality by Creighton, 1950a: 500; no lectotype designated). Primary type depositories: AMNH, MCZC.