Myrmica rubra

A widely distributed, common European species that has been introduced in the northeastern and northwestern United States and western Canada. It is unusual in being an invasive species in temperate habitats; most ants that have spread by human activities occur and are spread in tropical and subtropical areas.

Identification
A member of the rubra group. Yellowish brown. Sculpture dilute; frontal triangle and subspinal areas smooth and shining. Antennal scapes long and slender. Petiole node with short indistinct dorsal area sloping evenly without definite break to its junction with the postpetiole. Head Index: 79.5; Frons Index: 49.4; Frontal Laminae Index: 92.7. Length: 3.5-5.0 mm. (Collingwood 1979)

Distribution
Europe (in the south mostly in mountains), Siberia, to the east until Transbaikalia, to the north until Forest-Tundra Zone; in Transcaucasus and Middle Asian mountains is quite rare; introduced in northeastern and northwestern United States and western Canada.

Distribution based on Regional Taxon Lists
Nearctic Region: Canada, United States. Palaearctic Region: Andorra, Armenia, Austria, Belarus, Belgium, Bulgaria, China, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hungary, Iberian Peninsula, Japan, Jersey, Kyrgyzstan, Latvia, Liechtenstein, Lithuania, Luxembourg, Mongolia, Montenegro, Netherlands, Norway, Poland, Republic of Macedonia, Republic of Moldova, Romania, Russian Federation, Slovakia, Slovenia, Spain, Sweden, Switzerland, Ukraine, United Kingdom of Great Britain and Northern Ireland.

Biology
Radchenko and Elmes (2010): M. rubra is a eurytopic species distributed widely throughout Europe and West Siberia where it can dominate some habitats. It thrives in damp habitats, especially soils with high water tables or habitats in areas of high rainfall. However, it is seldom found living in tussocks on true bogs, in the manner of some populations of M. scabrinodis and M. ruginodis. In western Europe it is considered to be a species of damp meadows and is rarely found in woods and forests, the largest populations usually occur on west-facing slopes with heavy clayey (often limestone) soils, where it builds nests in the soil and under flat stones. These sites often have high rainfall and the moisture is held in the heavy soils. In eastern Europe (Russia, Ukraine etc.) it is considered to be more of a forest species inhabiting many different kinds of forests (except those with light, dry soils), where it builds nests in the soil under moss and in or under rotten wood. In central Europe M. rubra is often very abundant in grass on forest, woodland and hedgerow edges, and in Germany, Poland and France etc. it is particularly abundant in the longer vegetation at the edges of water meadows used for haymaking and grazing. Throughout its entire range it is associated with meadows bordering rivers and lakes. In recent years it has become important in nature conservation as the primary ant host of the endangered butterfly species Phengaris nausithous (Bergstrasser) (see papers in Settele et a!. 2005).

M. rubra colonies do not need a long season of high temperatures to complete their life cycles, in most habitats the ants do not become active until the end of April and are entering a pre-hibernation state by late September (Elmes 1982). They have an active basal physiology (compared to many other Myrmica species) that has adapted to local environments in different parts of its range. Habitat selection seems to be determined by a trade-off between sufficient insolation to complete their life cycle and maintaining a high humidity within the soil nest (assuming other factors such as food availability and nest site suitability being equal). Thus at sea level in the more oceanic climates of western Europe, woodlands are too cold in summer while east-facing meadows get too hot and dry whereas in the much more continental climates of eastern Europe, the hot summers enable them to live in woodlands which dessicate less rapidly than open meadows. Mountains of course, make their own local climates so that for example, in the Carpathians populations favour more open meadow habitats at higher altitudes that are ecologically very similar to the prime habitat in western Europe.

Generally, the microhabitat favoured by M. rubra colonies living by rivers and wet meadows ranges from open grass (about 10-20 cm tall) in the north and west of Europe to much longer grass and reeds (1-2 m tall) in southern and eastern habitats. Much less is known about its distribution in West Siberia: M. rubra is one of the commonest ants in various habitats of West and East Siberia (Reznikova 1983; Dmitrienko, Petrenko 1976) and is particularly common in rivers meadows in north-eastern Kazakhstan (M. Woyciechowski, pers. comm.). The principal competitors of M. rubra are other Myrmica species but in meadows it faces strong competition from Lasius niger (Czechowski 1985).

Morphologically M. rubra is comparatively stable over its very wide range (unlike, for example, M. scabrinodis, which is probably undergoing current speciation in Europe – see notes to that species), most of its local adaptation appears to have been physiological and perhaps behavioural. Consequently, given its abundance, it would be an ideal candidate to attempt phylogeographical history of its invasion of Europe using modern molecular analytical techniques. Until this occurs we can only hypothesise from whence M. rubra spread. It seems probable to us, that it survived the last ice age in Middle Asia or maybe the Balkans or southeast Europe, on so-called “tundra-steppes”, and spread rapidly into Europe along the great river margins as the ice melted. Coinciding with man's deforestation of Europe many new habitats were created in the oceanic part of Europe, the forests of which would have been generally too cold for colonisation. Thus in a sense M. rubra is pre-adapted to invade anthropogenic habitats (gardens, agrocoenoses) especially in areas of high rainfall. This might help explain why it has been a very successful invader of the eastern seaboard of USA and Canada. It is most useful to think of M. rubra in terms of “nests”, colonies can consist of single nests, or polycalic aggregations of several nests and even huge aggregations that can be considered as super-colonies (see Garnas et al. 2007). At a typical meadow site in Southern England nests were on average 1.8 m apart (Elmes 197 4a). Most studies to date show that individual nests contain from a few tens of workers to up to eight thousand with a mean of about 1,000 (Wardlaw and Elmes 1996); nests are usually polygynous with a mean of about 15 queens and nests hardly ever exceed a maximum density of 1 queen per 10 workers (Elmes 1973a). Remarkably average nest size does not differ notably from these estimates even in the super colonies of the USA (Garnas et al. 2007). In wild populations workers “turn-over” quite rapidly and live on average less than 2 years (Brian 1972) and most queens are equally short-lived (Elmes 1980; Seppa and Walin, 1996) .The density of queens in nests varies between populations in space and time (Elmes and Petal 1990), a statistical analysis of weather variables indicated that the nest population of both workers and queens increased as the mean late summer temperatures deviated from about 16°C, which was more or less the long-term average for the sites studied. It was suggested that the most probable explanation was that the local population structure was adapted to the long term conditions at a particular site and in years when conditions deviated from this, nests were less likely to fragment (see below) and so on average, were somewhat larger. This fits with the larger picture for local physiological adaptation by populations of Myrmica in different parts of their range (Elmes et. al. 1999) and the observations in particular for M. rubra (e.g. Brian 1973a; Kipyatkov 1979; Elmes and Wardlaw 1983a; Raybould and Pearson 1992). Nests are usually built into the soil and the design of the excavated nest is tailored to the conditions of the nest site (e.g. Evesham 1992). In coastal meadows M. rubra are less tolerant of salted soils compared to M. scabrinodis but nests can survive periodic inundation (Boomsma and De Vries 1980; Boomsma and lsaaks 1982). Young mated queens are available for much of the active year and are often recruited into nests (Elmes 1982) so that local populations can vary considerable for individual relatedness and level of effective polygyny (Seppa and Walin 1996). Consequently nest fission is a common way of reproduction in M. rubra. Nests frequently fragment in spring and in some circumstances become aggressive towards each other (Czechowski 1984). Often fragments recombine in autumn or they may remain associated as a polycalic colony. In some circumstances M. rubra populations may form huge polycalic colonies with hundreds of thousands or even millions of workers, like in some North America populations and very occasionally in some European populations (personal observation). In such populations it appears that there is a high level of food availability, nests grow rapidly and fragment but do not need to move far from the parent nest. This results in a very dense population of nests though individual nest sizes remain on average about 1000 workers. The proclivity for fragmenting into small colonies each containing several queens seems to be a useful adaptation to rapidly invading new habitat and at the same time incipient colonies are easily spread and introduced into new habitats by man's activities (in plant pots, roots of transplanted shrubs and trees – see Groden et al. 2005 and Garnas et. al. 2007). Although workers in supercolonies appear to be very tolerant towards their neighbouring colony members, they can be very aggressive towards other organisms, stinging people and other animals freely (personal observations); however, laboratory studies suggest that M. rubra workers do not have especially different aggressive responses compared to other members of the genus (De Vroey and Pasteels 1978). M. rubra have a well equipped sting apparatus (Billen 1986) and although some people react allergically to the venom, the sting and venom does not seem markedly different from that of other free-stinging myrmicines (e.g. Blum and Herman 1978). Most people (including one of us - AR) think that M. rubra stings seem particularly painful compared to other Myrmica species. However in the opinion of the other author (GWE) when individuals of other Myrmica are provoked into stinging (usually in hot conditions) a single sting can be equally painfully as that of M. rubra, perhaps even more so if the specimen is large: M. rubra having acquired its reputation because colonies are corporately aggressive and individuals sting rapidly and frequently even when fairly cool.

M. rubra is a generalist scavenger and predator hunting various small invertebrates (e.g. Petal 1967), but also utilize honeydew and nectar (flowers and extrafloral nectaries, e.g. Felton 1959), aphids and scale insects. They forage on trees and shrubs more frequently than any other Myrmica species (except perhaps M. ruginodis); though in Europe arboreal foraging is quite rare while in the supercolonies of Maine, USA very many M. rubra workers can be seen foraging high into the canopy (personal observations). M. rubra workers often forage in groups (e.g. Dlussky et al. 1978) and they lay and follow chemical foraging trails (e.g. Cammaerts-Tricot and Verhaeghe 1974; Cammaerts-Tricot et al. 1977). Single foragers (weighing about 2 mg) are able to exert pulling-forces of about 100 mg. developing a mean power of about 5.8 ergs/s (Sudd 1965), a third to a quarter of the strength and power exerted by Formica lugubris Zett. workers.

Winged sexuals (gynes and males) are produced in June and “mature” inside the nest until July. The ontogeny of larval development and caste determination has been extensively studied by M. V. Brian using M. rubra as a model species and has been found to be very complex; for example, the hormonal state of the queen influences larval hormone production and ontogeny (Brian 1959, 1974), trophic conditions are involved (Brian and Abbott 1977) as are the age and numbers of workers (Brian and Jones 1980), seasonality has an effect (Pearson and Raybould 1997) and even gut parasite load might have some impact (Pearson and Raybould 1998). A model based on these interactions show that gyne production might be periodic (Brian et al. 1981) and this may account for the observation that the mean size of workers and queens in nests is positively correlated with worker number and negatively correlated with queen number (Elmes 1974b).

Nuptial flights occur from late July and have been reported as late as October. Compared to many other Myrmica species, M. rubra mating swarms can be quite large aggregations and they have frequently been reported flying quite long distances to join swarms on church towers, high trees and mountain-tops (e.g. Hubbard and Nagell 1976; Woyciechowski 1990b; personal observations). We have on occasion observed nests having recruited a mixture of their own daughters and other young queens (all fertilised), but we are not sure whether their daughters mated in or near to the nest prior to joining the parent colony or flew to a distant swarm, mated and found their way home again. While the latter seems improbable it is what happens in the case of honey bees.

Bertelsmeier et al. (2015) examined elements of interspecific aggression between this species and several other highly invasive ants. In laboratory assays Myrmica rubra was adept at avoiding aggressive interactions. When confronted by workers of other invasive ant species M. rubra either acted indifferently or moved away.

Foraging/Diet
See the general biology discussion above for an overview of diet and foraging. Novgorodova (2015b) investigated ant-aphid interactions of a dozen honeydew collecting ants in south-central Russia. All of the ants studied had workers that showed high fidelity to attending particular aphid colonies, i.e, individual foragers that collect honeydew tend to return to the same location, and group of aphids, every time they leave the nest. Myrmica rubra showed no specialization beyond this foraging site fidelity. Foragers tended Chaitophorus populeti (Panzer) and Aphis pomi De Geer.

Bologna and Detrain (2015) examined foraging behavior in a laboratory experiment with M. rubra obtained from locations in Belgium. They found that the ants became satiated and showed a large decline over time in retrieval of elaiosome bearing seeds of Viola odorata. Seeds were offered once a week for 5 consecutive weeks and again at week 12. A similar experiment with dead fruit flies showed a consistent foraging response where the ants collected most of the offered fruit flies.

Introduced Range Studies
Naumann and Higgins (2015) examined the influence of this species on native insects. Abstract: Pitfall trapping revealed that the European fire ant, Myrmica rubra (Linnaeus) (Hymenoptera: Formicidae), represents an unusual example of a temperate invasive ant species. In British Columbia, Canada, M. rubra populations are associated with a decreased incidence and abundance of other ant species in three different plant communities when compared with M. rubra-free control areas. M. rubra represented more than 99.99% of the total ant fauna caught in the infested areas, and the numbers of M. rubra captured in the plant communities ranged from over 10 times to over 1300 times the total number of all ants collected in corresponding M. rubra-free areas. Total numbers of some taxa of insects and non-insect arthropods, including those likely to be competitors or prey of M. rubra, were reduced where the invasive species was present. Biodiversity indexes for the overall suite of captured arthropod species were lower where M. rubra was present in all three plant communities but most of this decrease can be attributed to the difference in the ant fauna.

Experimental Studies - Social Immunity
Diez et al. (2015), a study examining pathogens and colony hygiene - Abstract: Ants have developed prophylactic and hygienic behaviours in order to limit risks of pathogenic outbreaks inside their nest, which are often called social immunity. Here, we test whether ants can adapt the “social immune response” to the level of pathogenic risk in the colony. We challenged Myrmica rubra colonies with dead nestmates that had either died from being frozen or from infection by the fungus Metarhizium anisopliae. Ant survival was compromised by the presence of the fungus-bearing corpses: workers died faster with a significantly lower survival from the 4th day compared to workers challenged with freeze-killed corpses. When faced with fungus-bearing corpses, workers responded quickly by increasing hygienic behaviours: they spent more time cleaning the nest, moving the corpses, and self-grooming. Ants in fungus-threatened colonies also decreased contact rates with other workers, and moved corpses further in the corners of the nest than in colonies in contact with non-infected corpses. These results show that ant colonies are able to assess the risk level associated with the presence of corpses in the nest, and adjust their investment in terms of hygienic behaviour.

Fungi
This taxon is a host for the fungi (Shrestha et al., 2017) and (Espadaler & Santamaria, 2012).

Nomenclature

 *  rubra. Formica rubra Linnaeus, 1758: 580 (w.) EUROPE. Latreille, 1802c: 248 (q.m.); Wheeler, G.C. & Wheeler, J. 1953a: 118 (l.); Hauschteck, 1965: 325 (k.). Combination in Myrmica: Latreille, 1804: 179. Senior synonym of laevinodis (and its junior synonyms bruesi, champlaini, longiscapus): Yarrow, 1955b: 114; Arnol'di, 1970b: 1839; Boven, 1977: 115; Arnol'di & Dlussky, 1978: 530; Collingwood, 1979: 52; Seifert, 1988b: 5; of europaea: Radchenko, Czechowski & Czechowska, 1997: 483; Czechowski, Radchenko & Czechowska, 2002: 17; of microrubra: Steiner, Schlick-Steiner, Konrad, et al. 2006: 777. Current subspecies: nominal plus khamensis, neolaevinodis. See also: Emery, 1908a: 169; Brian, M.V. & Brian, A.D. 1949: 393; Smith, D.R. 1979: 1350; Pearson, 1981: 75; Seifert, 1988b: 5; Onoyama, 1989a: 131; Atanassov & Dlussky, 1992: 83; Radchenko & Elmes, 2010: 228.
 * laevinodis. Myrmica laevinodis Nylander, 1846a: 927, pl. 18, figs. 5, 31 (w.q.m.) FINLAND. Subspecies of rubra: Forel, 1874: 76; Emery & Forel, 1879: 460; Wheeler, W.M. 1906d: 315; Emery, 1914d: 156; Forel, 1915d: 28; Menozzi, 1918: 82; Karavaiev, 1927c: 259; Creighton, 1950a: 104. Status as species: Saunders, E. 1880: 215; André, 1883a: 316; Dalla Torre, 1893: 110; Ruzsky, 1905b: 662; Bondroit, 1912: 351; Donisthorpe, 1915d: 110; Bondroit, 1918: 104; Müller, 1923: 40; Finzi, 1926: 83; Stitz, 1939: 78; Holgersen, 1940: 184; Novak & Sadil, 1941: 76; Weber, 1947: 441; Bernard, 1967: 119; Baroni Urbani, 1971c: 22; Kutter, 1977c: 65. Senior synonym of longiscapus: Mayr, 1863: 433; of champlaini: Smith, M.R. 1951a: 789; of bruesi: Creighton, 1950a: 104. Junior synonym of rubra: Yarrow, 1955b: 114; Arnol'di, 1970b: 1839; Arnol'di & Dlussky, 1978: 530; Collingwood, 1979: 52; Seifert, 1988b: 5; Radchenko, 2007: 30.
 * europaea. Myrmica laevinodis var. europaea Finzi, 1926: 84 (w.) NORWAY. [First available use of Myrmica rubra subsp. champlaini var. europaea Forel, 1911h: 457; unavailable name.] Santschi, 1931b: 339 (m.). Subspecies of laevinodis: Stitz, 1939: 83; of rubra: Bolton, 1995b: 279. Junior synonym of rubra: Radchenko, Czechowski & Czechowska, 1997: 483; Czechowski, Radchenko & Czechowska, 2002: 17.
 * bruesi. Myrmica laevinodis var. bruesi Weber, 1947: 453 (w.q.m.) U.S.A. [First available use of Myrmica rubra subsp. laevinodis var. bruesi Wheeler, W.M. 1906a: 38; unavailable name.] Junior synonym of laevinodis: Creighton, 1950a: 104.
 * champlaini. Myrmica rubra r. champlaini Forel, 1901h: 80 (w.) CANADA. Subspecies of laevinodis: Weber, 1947: 454; of rubra: Creighton, 1950a: 103. Junior synonym of laevinodis: Smith, M.R. 1951a: 789.
 * longiscapus. Myrmica longiscapus Curtis, 1854: 213, pl. 23, figs. 11-14 (w.q.m.) GREAT BRITAIN. Junior synonym of laevinodis: Mayr, 1863: 433.
 * microrubra. Myrmica microrubra Seifert, 1993: 10, figs. 1, 4 (q.m.) GERMANY. Junior synonym of rubra: Steiner, Schlick-Steiner, Konrad, et al. 2006: 777. See also: Czechowski, Radchenko & Czechowska, 2002: 19; Radchenko & Elmes, 2003a: 236.

Etymology
Radchenko and Elmes (2010) - from the Latin word rubra = red, to describe its generally reddish colour.