Myrmica arnoldii

Despite its typically "socially-parasitic" features, M. arnoldii has only been found living in independent colonies. Dlussky reported that in Siberia colonies lived mainly in larch forests, but also in steppe-like habitats, with nests usually being built in decaying wood and rarely in the soil. This accords with the more recent samples from Mongolia taken by M. Woyciechowski (Krakow): colonies were living on northern and western slopes in mountain Larix-Betula forest at about 1000 m altitude, nests were usually in rotten tree stumps but sometimes in the soil or moss, they were quite populous and usually polygynous. We suggest that M. arnoldii might be a temporary social parasite, or represents a hypothetical step in the evolution of social parasites, or even is a social parasite that has reverted to a free-living lifestyle. In any case, this interesting species would make an ideal subject for further study. (Radchenko and Elmes 2003)

Identification
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).

Key to Myrmica of species of East Siberia, Russian Far East, Mongolia, Korean Peninsula, northern China, and Japan

Distribution
South Siberia from Tuva to eastern Transbaikalia, and Mongolia.

Distribution based on Regional Taxon Lists
Palaearctic Region: Mongolia, Russian Federation.

Nomenclature

 *  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.

Etymology
Radchenko and Elmes (2010) - M. arnoldii: this species was dedicated to the famous Russian myrmecologist K. V. Arnoldi