Myrmica arnoldii

Despite its typically "socially-parasitic" features, M. arnoldii has only been found living in independent colonies. Jansen et al. (2010) treats it as a temporary parasite and suggests its likely host is Myrmica lobicornis. 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
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).

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

References based on Global Ant Biodiversity Informatics

 * Aibek U., C. Sonomdagva, and S. Yamane. 2006. A preliminary survey on the species composition and nesting habits of ants in the Bogdkhan Mountain region, North Central Mongolia. ANeT Newsletter 8: 11-15.
 * Bayartogtokh B., U. Aibek, S. Yamane, and M. Pfeiffer. 2014. Diversity and biogeography of ants in Mongolia (Hymenoptera: Formicidae). Asian Myrmecology 6: 1-20.
 * Dlussky G. M., and B. Pisarski. 1970. Formicidae aus der Mongolei. Ergebnisse der Mongolisch-Deutschen Biologischen Expeditionen seit 1962, Nr. 46. Mitteilungen aus dem Zoologischen Museum in Berlin 46: 85-90.
 * Jansen G., R. Savolainen, K. Vespalainen. 2010. Phylogeny, divergence-time estimation, biogeography and social parasite–host relationships of the Holarctic ant genusMyrmica(Hymenoptera: Formicidae). Molecular Phylogenetics and Evolution 56: 294-304.
 * Pisarski B. 1969. Fourmis (Hymenoptera: Formicidae) de la Mongolie. Fragmenta Faunistica (Warsaw). 15: 221-236.
 * Radchenko A. G., and G. W. Elmes. 2003. A taxonomic revision of the socially parasitic Myrmica ants (Hymenoptera: Formicidae) of the Palaearctic region. Annales Zoologici (Warsaw) 53: 217-243.
 * Yamane S. 2007. Ants of Mongolia. The Nature and Insects. 42: 20-25
 * Yamane S., and U. Aibek. 2012. Distribution of Myrmica species (Hymenoptera, Formicidae) in Mongolia. Japanese Journal of Systematic Entomology 18(1): 171-185.
 * Yamane S., and U. Aibek. 2012. Distribution of Myrmica species (Hymenoptera, Formicidae) in Mongolia. Jpn. J. Syst. Ent. 18(1): 171-185.