Leptothorax (Leptothorax) curvispinosus subsp. ambiguus Emery, 1895d: 320 (w.) U.S.A. (South Dakota). Nearctic.

Primary type information: Type-material: syntype workers (number not stated). Type-locality: U.S.A.: South Dakota, Hill City [43°56′N 103°34′W] (Pergande) (by restriction of Creighton, 1950a: 263). Type-depositories: AMNH, MCZC, MSNG, USNM. Type-specimen: CASENT0904763. Type notes: Other syntype localities: U.S.A.: Ohio, Cleveland (Wasmann), U.S.A.: New York (Schmelter).