A member of the arnoldii group. Radchenko and Elmes (2010) - M. arnoldii shares several morphological features with the species of incompleta-group, e.g. shape of scape and frontal lobes in the female castes, and short scape of males. M. arnoldii well differs from almost all other free-living Palaearctic Myrmica species by several features, many of which are considered as the "socially-parasitic syndrome": males have 12-segmented antennae (this feature led Arnoldi 1968b. erect subgenus Dodecamyrmica); the petiole and postpetiole of all castes have ventral lobes, which are most developed in queens; the spurs on tibiae of mid- and hind legs are often reduced (more frequently in female castes); they are small, queens are little larger than workers (AL of workers, queens and males < 1.5, 1.8 and 1.6 mm, respectively) (see also Radchenko and Elmes 2003a).
South Siberia from Tuva to eastern Transbaikalia, and Mongolia.
Palaearctic Region: Mongolia, Russian Federation (type locality).
arnoldii. Myrmica arnoldii Dlussky, 1963: 191, figs. 1, 4, 5 (w.) RUSSIA. Arnol'di, 1968: 1803 (q.m.). Combination in M. (Dodecamyrmica): Arnol'di, 1968: 1803. See also: Francoeur, 1981: 759; Radchenko & Elmes, 2003a: 222; Radchenko & Elmes, 2010: 94.
Radchenko and Elmes (2003) -Taxonomic notes. This unusual species has a rather uncertain taxonomic position. It well differs from almost all other free-living Palaearctic Myrmica species by several features, many of which are considered as socially-parasitic: males have 12-jointed antennae (this feature led Arnoldi 1968 describe subgenus Dodecamyrmica); the petiole and postpetiole of all castes have ventral lobes, which are most developed in queens; the spurs on tibiae of mid- and hind legs are often reduced (more frequently in female castes); they are small, queens are little larger than workers (AL workers, queens and males < 1.5, 1.8 and 1.6 mm, respectively). The body sculpture, colour and shape of petiole (subtriangular when viewed in profile) of queens are similar to that of Myrmica myrmicoxena, and they differ by their slightly larger size and wider frons. Males differ by the number of antennal segments, 12 rather than 13.