Exochus pygmæus Cresson, 1864:285, ♂. ♂, Illinois (leg. Dr. Samuel Lewis); Davis, 1897Davis, G.C. 1897. A review of the Ichneumonid subfamily Tryphoninae. Transactions of the American Entomological Society 24 (3/4):193-348.:213, Type (Amer. Ent. Soc.); Townes & Townes, 1959Townes, H.K. & M. Townes 1959. Ichneumon-flies of America north of Mexico: 1. Subfamily Metopiinae. Bulletin of the United States National Museum 216 (1):1-318.:124, Type ♀, 'xm' = xf (Philadelphia). Synonymized with Triclistus pallipes Holmgren, 1873 by Townes & Townes, 1959Townes, H.K. & M. Townes 1959. Ichneumon-flies of America north of Mexico: 1. Subfamily Metopiinae. Bulletin of the United States National Museum 216 (1):1-318.:124. - Cresson, 1868Cresson, E.T. 1868. A list of Ichneumonidae of North America, with descriptions of new species. Part II. Transactions of the American Entomological Society 2:89-114. (distribution). - As Triclistus pygmaeus: - Davis, 1897Davis, G.C. 1897. A review of the Ichneumonid subfamily Tryphoninae. Transactions of the American Entomological Society 24 (3/4):193-348. (distribution); Dalla Torre, 1901-1902Dalla Torre, C.G. 1901-1902. Catalogus Hymenopterorum hucusque descriptorum systematicus et synonymicus. — Volumen III: Trigonalidae, Megalyridae, Stephanidae, Ichneumonidae, Agriotypidae, Evaniidae, Pelecinidae. Pars II. Breitkopf & Härtel, Leipzig. VIII + 1141. (distribution); Krombein et al., 1979Krombein, K.V., P.D. Hurd, D.R. Smith & B.D. Burks 1979. Catalog of Hymenoptera in America North of Mexico. Volume 1. Symphyta and Apocrita (Parasitica). Smithsonian Institution Press, Washington D.C. 1-1198. (distribution).
Triclistus taiwanensis Uchida, 1932:267 Synonymized with Triclistus pygmaeus (Cresson, 1864) by Krombein et al., 1979Krombein, K.V., P.D. Hurd, D.R. Smith & B.D. Burks 1979. Catalog of Hymenoptera in America North of Mexico. Volume 1. Symphyta and Apocrita (Parasitica). Smithsonian Institution Press, Washington D.C. 1-1198.:554.