Myrmica ruginodis

A widespread species, transpalaearctic and also introduced in North America, that can be common in a variety of habitats.

Identification
Radchenko and Elmes (2010) - A member of the rubra group. For quite a long period in the middle of the 20th century the name was synonymised with Myrmica rubra before Yarrow (1955) decided that really M. laevinodis was the true synonym of M. rubra. M. ruginodis can be confused with M. rubra (=laevinodis) in some parts of Europe, especially when solitary specimens are examined; however Brian and Brian (1951) demonstrated that a clear discrimination can be made on the basis of propodeal spine length. The simplest way of discrimination between the two species in the field is to examine the length and shape of the spines (seen in profile) with a x10 hand lens.

Collingwood (1979) - Pale to dark reddish brown. Propodeal spines long and robust; area between their bases laterally striate, frontal triangle smooth and shining. Head and alitrunk coarsely longitudinally rugulose. Antennal scapes long and slender, gently and obliquely curved near their base. Petiole in profile massive with truncate dorsal area and abrupt step posteriorly to its junction with the postpetiole gives the easiest distinction from Myrmica rubra (L.). Head Index: 77.5; Frons Index: 48.3; Frontal Laminae Index: 91.3. Length: 4.0-6.0 mm.

Distribution
Transpalaearctic species, distributed from Atlantic to Pacific Oceans, including Japan; in the south - only in mountains, absent from Middle Asian mountains. Introduced to North America.

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Palaearctic Region: Albania, Andorra, Armenia, Austria, Belarus, Belgium, Bulgaria, Channel Islands, China, Croatia, Czech Republic, Democratic Peoples Republic of Korea, Denmark, Estonia, Finland, Georgia, Germany, Greece, Hungary, Iberian Peninsula, Latvia, Lithuania, Luxembourg, Mongolia, Netherlands, Norway, Poland, Portugal, Republic of Korea, Republic of Macedonia, Romania, Russian Federation, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom of Great Britain and Northern Ireland.

Biology
Radchenko and Elmes (2010):

M. ruginodis is the species of Myrmica that is most adapted to cool temperatures, at least of those species studied in detail so far, though see data for Myrmica kamtschatica (Berman et al. 2010). Both the workers and brood have an active basal physiology (Elmes et. al. 1999; Nielsen et al. 1999) that, for example, enables it to complete its life cycle in the same time as a Myrmica sabuleti nest but living at a mean nest temperature that is 4-5°C lower (Elmes and Wardlaw 1983a). As in the case of Myrmica rubra local populations appear to have adapted physiologically to local environments (Elmes et. al. 1998). Consequently, M. ruginodis is found in cooler habitats: all kinds of forests, scrublands, alpine meadows, woodland clearings, moorlands and bogs, but generally it avoids both very wet and dry open sites. It is widespread and abundant in these habitats over most of its range, however M. ruginodis is much less tolerant than Myrmica rubra to anthropogenic pressure (grazing, mowing etc.). Like all Myrmica, latitude and altitude determines the species’ basic distribution: in the far north it lives at more or less sea level, while at southern latitudes it is mainly a montane species. At any particular altitude and latitude the degree to which sunlight can penetrate the canopy (be it forest, scrub or long grass) in any habitat will determine the range of potential nest-site temperatures available to the ants (e.g. see Brian and Brian 1951). Its adaptation to cooler nest-sites (above) enables it to live in cool northern forests and so it is one of the commonest ant species in the Forest Zone of the Palaearctic. In forests and woodlands M. ruginodis prefers to build its nests in (and under) rotten wood, branches and even trunks of fallen trees. However, in managed forest its preferred habits is rotten tree stumps (Brian and Brian 1951; Franch and Espadaler 1988) and often one can find a nest in more or less every stump. In grasslands it prefers to build nests in the surface of the soil in and among the roots of grass (particularly Molinea species - see Elmes 1978b). In wetter boggy areas nests are usually constructed in the tops of moss tussocks. In spring the workers build a small solarium above their nest where the overwinter brood is reared; the solaria are usually a mixture of soil particles and dead vegetation, pieces of grass, moss etc. and can be quite warm in sunshine. Such nests are often temporary and the ants migrate to a new site every few months, often one can find a series of nests belonging to the same colony: first the active nest, another a meter or so away that is in the process of construction and occupied by a few workers and brood, and an old nest a meter or so in the opposite direction occupied by just a few workers and sometimes, an even older nest a meter or so further away from that (personal observations). It was such a colony that Forel observed in 1866 (see notes on var. ruginodolaevinodis above). In more open grassland where colonies build more permanent nests in the soil and under stones, the substrate affects nest densities (Fedoseeva and Demchenko 1997).

Early studies on caste determination, worker behaviour and larval ontogeny were made using M. ruginodis [Sic!] as the model species (Weir 1958c, 1959a; Brian 1951b) before M. V. Brian and his co-workers switched to M. rubra. Also, M. ruginodis was one of the first Myrmica species studied ecologically (see Pickles 1940 and e.g. Brian 1950) and more recently interesting life history traits of some populations have resulted from molecular genetical studies (see Seppa 1992,1994; Seppa and Pamilo 1995). M. ruginodis workers are among the species that are most prolific in producing worker-laid eggs (Wardlaw and Elmes 1998). Understanding its ecology has become important to nature conservation because M. ruginodis one of the primary hosts for the endangered butterfly Phengaris alcon (see papers in Settele et al. 2005). In particular, understanding the species and colony recognition odours and their mimicry by the lepidopteran caterpillars is important, the cuticular surface chemicals of M. ruginodis are quite distinct from those of M. rubra (e.g. Elmes et. al. 2002). Like the other Mynnica species, workers lave long been known to stridulate (Swinton 1878).

The workers are generalist predators, hunting small invertebrates (e.g. Brian 1955b) and forming trophobiosis with aphids, though this is generally less developed than is the case for M. rubra. Some studies have been made of recruitment to food sources (Cammaerts and Cammaerts 1980). In many habitats the eliasomes of various seeds play an important role in the diet of M. ruginodis and they have important mutualistic interaction with the plants (e.g. Kjellsson 1985; Mark and Olsen 1996; Gammans et al. 2006).

It is in the studies of behaviour and population ecology of M. ruginodis that the concept of var. macrogyna and var. microgyna diverges from the taxonomic notion (see taxonomic notes above). As the two forms have no status in taxonomy we refer to them as “normal” and “microgyne” M. ruginodis respectively. Brian and Brian (1949, 1955a) showed that in west Scotland the queens in polygynous colonies of M. ruginodis were visibly smaller (microgynes) than those in monogynous (normal) colonies (mean head width 1.02 ± 0.06 mm vs. 1.13 ± 0.04 mm), intermediate sized queens (head width about 1.06 mm were quite rare). They showed that apart from being more polygynous, microgyne colonies have workers that are generally less aggressive and more tolerant of other workers and queens compared to workers from normal colonies. Microgyne colonies recruit new queens and reproduce by colony fission whereas normal queens are more likely to attempt to establish new colonies by independent (or pleometrotic) colony foundation. Thus microgyne colonies are adapted to spread rapidly into and monopolise habitats that are stable in the long term (such as grassy moorland) and the original colonising gene pool might remain in such a habitat for many hundreds of years. Normal queens are better at dispersing into new habitats where they form relatively short-lived monogynous colonies, though such colonies sometimes engage in secondary recruitment (Seppa et al. 1995) and may even recruit some microgynes. Later we confirmed the size dimorphism shown by Brian and Brian and showed that most populations have at least a small proportion of microgyne queens (Elmes 1978a); also we made the interesting observation that the overall proportion of morphological variation of workers, expressed at the population level, was about the same for both forms but a much higher proportion of this (ca 60%) was expressed within individual microgyne colonies compared to only 40% within normal colonies (Elmes and Clarke 1981). This was compatible with a higher number of unrelated queens producing workers in the microgyne colonies. We also showed that there were differences in the pattern of brood production and control of castes between the two forms (Elmes and Wardlaw 1983a, b).

It is clear that the size and behavioural differences represent a true polymorphism in M. ruginodis that enables the species to exploit and monopolise a much wider range of habitats than it otherwise could. The fact that M. rubra (= laevinodis) also has a semi-parasitic, microgyne form combined with the nomenclatural problems from 1935-1955 (see notes to M. rubra) has confused many people. Synthesisers have often confounded the results for the two species. We recommend that anyone interested in these problems should consult the original literature and bear in mind the name changes. To date we have no understanding of the underlying genetical mechanisrl1 behind the polymorphism, as far as we know the two forms “breed true” and nobody has been able to produce a microgyne queen from a normal mother or vice-versa. As a general rule, monogynous (or with two or three queens) colonies usually have only normal queens, whereas highly polygynous colonies often have a mixture of queens, a few normal queens and many more microgynes. Normal queens in microgyne colonies apparently have a more “microgyne-like” tolerant behaviour, which begs the question as to whether normal queens have an ethological dimorphism with some having an intrinsic microgyne-like behaviour and others having a “monogynous normal” behaviour as described by Brian and Brian (1955). This question still remains to be resolved. Microgyne colonies average about 6 queens (with> 20 queens being common), while normal colonies average 1 queen (with 4-5 queens being very unusual). Surprisingly, the average worker populations of the two types of colony do not vary significantly, the best overall estimate of colony size in Britain is about 500 workers (Elmes and Keller 1993; Wardlaw and Elmes 1996). On upland moorland (> 200 m a.s.l.) colonies are smaller (about 400 workers) than on lowland southern heaths and lowland Scottish moors (700 and 1200 workers respectively), the difference between southern England and Scotland being statistically significant. There has been considerable debate as to whether Japanese populations of M. ruginodis have a microgyne form (Mizutani 1981; Kasugai et al. 1983; Ichinose 1990; Kikuchi et al. 1999). We suggest that probably the microgyne form is not present in the Far East and that M. kotokui populations occupy the ecological niche normally used by microgyne M. ruginodis in the west; this remains to be fully tested.

Nuptial flight occurs in August-September (in mountains as late as mid-October) and over the years have been regularly reported in the literature (e.g. Beare 1913; O'Rourke 1940) and swarms, comprising mostly of males, often have been taken in light traps (e.g. Elmes and Webb 1985). Brian and Brian (1949, 1955) showed that microgynes are more likely to mate in or near to the nest in local swarms and join existing colonies whereas normal queens are more likely to fly to larger more distant nuptial swarms and attempt independent colony foundation. However, in regions where the microgyne form is found, mixed swarms are common but there is no evidence to support the idea of assortative mating between the two forms (Elmes 1991), although larger males are more likely to find a mate than smaller ones. Perhaps only the size of the mother is important in determining the nature of her female offspring and the parentage of the males is not important (a sort of maternally mitigated polymorphism). Similar ideas were discussed in relation to M. lonae (see above).

Finally, the question of the stinging-abilities of M. ruginodis: like most Myrmica species the workers readily deploy their sting when defending their nest against intruders. Their venom is quite potent (Jentsch 1969a, b) but the general perception is that M. ruginodis workers are much less aggressive towards human disturbance than M. rubra and that when provoked into stinging, the sting is less painful (see ecological notes for M. rubra). However, in warm humid conditions on Hokkaido Island Japan we found a dense population of M. ruginodis nesting on the stumps of felled trees in a spruce forest. These workers were very aggressive attacking as freely and stinging as painfully as the worst M. rubra colonies we have observed. Furthermore, in these conditions M. kotokui stung freely and painfully. Thus willingness to sting and the amount of venom injected appears to be an interaction between the level of basic behavioural aggressive responses (probably varying between species and populations) and temperature; it would be interesting to test this under controlled conditions.

Collingwood (1979) - This common species is abundant throughout the woodlands and high moorlands of North Europe to the North Cape. Brian and Brian (1949) showed that this species occurred in two incompletely dimorphic races, one polygynous with many small queens approaching the microgyne condition and one monogynous with single large queens which they termed var. microgyna and var. macrogyna respectively; microgyna was found to readily accept strange queens and to occur in more stable habitats often forming groups of nests as is common with Myrmica rubra; macrogyna is more aggressive and hostile to strange queens, has more populous nests and is more generally distributed, predominating in woodland and more transitory habitats (Brian and Brian, 1955). Both forms occur in Scandinavia but cannot in conventional taxonomy be regarded as either distinct species or biotopic subspecies because of wide overlap in morphology and habitat. Mating flights occur in August near or on the ground.

Nomenclature

 * dimidiata. Myrmica dimidiata Say, 1836: 293 (q.) U.S.A. Junior synonym of ruginodis: Weber, 1947: 448.
 *  ruginodis. Myrmica ruginodis Nylander, 1846a: 929, pl. 18, figs. 5, 30 (w.q.m.) FINLAND. Hauschteck, 1965: 325 (k.). Subspecies of rubra: Forel, 1874: 76; Emery & Forel, 1879: 460; Ruzsky, 1904a: 288; Bondroit, 1910: 498; Forel, 1915d: 28; Menozzi, 1918: 82; Karavaiev, 1927c: 258; of laevinodis: Mayr, 1886d: 450; Ruzsky, 1902d: 29. Junior synonym of rubra: Santschi, 1931b: 339. Status as species: Saunders, E. 1880: 214; André, 1883a: 317; Nasonov, 1889: 33; Forel, 1892i: 315; Bondroit, 1912: 351; Donisthorpe, 1915d: 115; Bondroit, 1918: 103; Santschi, 1919e: 244; Müller, 1923: 41; Finzi, 1926: 85; Stitz, 1939: 83; Novak & Sadil, 1941: 76; Holgersen, 1942: 8; Collingwood, 1958b: 68; Bernard, 1967: 120; Collingwood & Yarrow, 1969: 56; Kutter, 1977c: 67; Arnol'di & Dlussky, 1978: 530; Collingwood; 1979: 53; Seifert, 1988b: 6; Atanassov & Dlussky, 1992: 86. Senior synonym of diluta: Mayr, 1861: 63, Radchenko, 2007: 28; of dimidiata: Weber, 1947: 448; of ruginodolaevinodis: Bernard, 1967: 120; Boven, 1977: 115; of mutata: Seifert, 1988b: 6; of macrogyna, microgyna: Bolton, 1995b: 282; of silvestrii, sontica, yoshiokai: Radchenko & Elmes, 2010: 236. See also: Radchenko, 2007: 30.
 * diluta. Myrmica diluta Nylander, 1849: 41 (w.) RUSSIA. Junior synonym of ruginodis: Mayr, 1861: 63; Radchenko, 2007: 28.
 * ruginodolaevinodis. Myrmica rubra var. ruginodolaevinodis Forel, 1874: 78 (q.m.) SWITZERLAND. Raised to species: Stitz, 1917: 347. Subspecies of rubra: Finzi, 1926: 86; Stitz, 1939: 84; Sadil, 1952: 241. Junior synonym of ruginodis: Bernard, 1967: 120; Boven, 1977: 115.
 * silvestrii. Myrmica ruginodis var. silvestrii Wheeler, W.M. 1928d: 100 (w.) JAPAN. Subspecies of rubra: Weber, 1947: 451. Raised to species: Collingwood, 1976: 301. Junior synonym of ruginodis: Radchenko & Elmes, 2010: 236.
 * sontica. Myrmica kurokii var. sontica Santschi, 1937h: 367 (w.) JAPAN. Currently subspecies of kurokii: Weber, 1947: 470. Junior synonym of ruginodis: Radchenko & Elmes, 2010: 236.
 * yoshiokai. Myrmica rubra subsp. yoshiokai Weber, 1947: 451 (w.) JAPAN. Raised to species: Collingwood, 1981: 26. Junior synonym of ruginodis: Radchenko & Elmes, 2010: 236.
 * macrogyna. Myrmica rubra var. macrogyna Brian, M.V. & Brian, A.D. 1949: 397 (q.m.) GREAT BRITAIN. Junior synonym of ruginodis: Bolton, 1995b: 281.
 * microgyna. Myrmica rubra var. microgyna Brian, M.V. & Brian, A.D. 1949: 397 (q.m.) GREAT BRITAIN. Junior synonym of ruginodis: Bolton, 1995b: 281.
 * mutata. Myrmica rubra var. mutata Sadil, 1952: 242, fig. I (w.) CZECHOSLOVAKIA. Junior synonym of ruginodis: Seifert, 1988b: 6.

Etymology
Radchenko and Elmes (2010) - from a combination of the Latin words ruga = wrinkle and nodus = knot or lump, to describe the rugose surfaces of the petiole and postpetiole.