Myrmica schencki

Host for the Mountain Alcon Blue (Phengaris rebeli) butterfly.

Identification
Radchenko and Elmes (2010) - M. schencki typifies the schencki species group. Its workers are characterized by the presence of a big vertical lobe at the scape base, by the well-developed petiolar peduncle and not-angled petiolar node (seen in profile) and especially, by the very narrow frons (mean FI 0.23); after Myrmica ravasinii, it has the second narrowest frons among all known Myrmica species in the World. M. schencki is fairly stable morphologically. It most resembles Myrmica koreana,Myrmica caucasicola and Myrmica obscura, but differs from them by its narrower frons. Also the males of all these forms are fairly well distinguishable (see also Radchenko, Elmes and. Alicata 2006; Elmes et al. 2009). In Europe, M. schencki quite often was confused with Myrmica lobicornis, though workers of the latter have the wider frons (FI > 0.27), shorter propodeal spines, and the short petiole with weakly developed peduncle and almost straight, quite steep anterior face that meets with the dorsal one at a sharp right or even acute angle. When males are available such confusions should not occur because M. lobicornis males have a much longer scape.

Collingwood (1979) - Brownish red with gaster and sometimes head darker. Frontal triangle striate. Antennal scape sharply angled near base, with an upright flange at the bend fitted closely into the thin divergent frontal ridge. Frons very narrow, about 1/4 head width. Mesopropodeal furrow shallow and postpetiole low, somewhat cubical in profile and spherical from above. Head Index: 88.4; Frons Index: 24.5; Frontal Laminae Index: 63.3. Length: 4.0-5.5 mm.

Distribution
South Europe to South Scandinavia.

Distribution based on Regional Taxon Lists
Palaearctic Region: Andorra, Austria, Belarus, Belgium, Bulgaria, Canary Islands, China, Croatia, Czech Republic, Denmark, Estonia, Finland, Georgia, Germany, Greece, Hungary, Iberian Peninsula, Italy, Kyrgyzstan, Latvia, Lithuania, Montenegro, Netherlands, Norway, Poland, Republic of Moldova, Romania, Russian Federation, Slovakia, Slovenia, Spain, Sweden, Switzerland, The former Yugoslav Republic of Macedonia, Ukraine, United Kingdom of Great Britain and Northern Ireland.

Biology
Throughout most of its northern distribution, M. schencki is associated with hot, dry grassland habitats including calcareous grassland, glacial sand deposits and seaboard sand-dunes. In its southern distribution it is associated with hot sub-alpine grassland. Much of its distribution seems to coincide with species of Tetramorium and Tapinoma, which are dominant species in such habitats; we have often recorded and excavated M. schencki nests from the middle of Tetramorium caespitum territories: T. caespitum can defend discrete territories that contain several polycalic nest centres connected by tunnels (e.g. see Brian and Elmes 1974). The common factor appears to be the need for relatively high soil temperatures but not completely arid conditions. In biotopes where the soil is potentially very arid, e.g. the sand-dunes of NW Europe, the sub-alpine pastures of the Southern Alps and limestone pavement as in the Burren, Ireland, M. schencki only occurs if there is a relatively high rainfall, which stops complete desiccation of the soils. Myrmica specioides is the only European Myrmica species that can tolerate similarly hot habitats. In many places its main competitors are ants from other genera and we believe that this contributes to its habit of building a small woven funnel at its nest entrance in which a “guard-worker” sits with its head more or less blocking the entrance. Tarbinsky (1981) showed that in the eastern part of its range M. schencki has rather limited foraging distances which generally agrees with our observations.

A population of M. schencki living on sandy soil In Jutland, Denmark has been studied by several authors. Elmes and Abbott (1981) showed that colonies averaged about 1 queen and 300 workers, and the overall mean head widths were 1.19 mm and 1.04 mm for queens and workers respectively. The workers were generally bicoloured but in some colonies a proportion of workers were a uniform gingery orange colour (not to be confused with the pale yellow of callow workers); no queens of this colour were noted but a few queens were almost completely dusky black. Thus colour is quite variable in this species. On the same site nest densities of 0.13 nests per m2 with an estimated 47 workers per m2 (Jensen 1976), giving an estimated colony size of about 250 workers which accords well with the later estimate. This population was shown to have a distinct diurnal foraging activity and was most active when soil surface temperatures were in the range 15-30°C, relative humidity did not affect foraging activity (Nielsen 1981a), a finding confirmed at another site (Nielsen 1981b).

M. schencki has become important to nature conservation study in recent decades because it is a primary host of the larvae of the parasitic butterfly Phengaris rebeli (Hir.) (Settele et al. 2005). Numerous nests have been excavated by different teams from many parts of Europe, and the' general consensus is that the population structure outlined above is typical. This work has led to the development of a spatially explicit simulation model to describe the interaction between M. schencki and M. sabuleti, its main Myrmica competitor on many P. rebeli sites. These models suggest that underlying heterogeneity of “habitat quality” colony fission and the ability to pre-empt a nest site is important to the spatial pattern of nest distribution (e.g. see Elmes et al. 1996; Clarke et al. 1997 and references therein).

An important aspect of the interaction between M. schencki and the larvae of P. rebeli is the ability of the caterpillars to mimic various ant signals. Consequently the cuticular chemicals of the ants have been identified (e.g. Elmes et al. 2002) and how they interact with caterpillar recognition (e.g. Elmes et al. 2004; Schrbnrogge et al. 2004). One of the most interesting discoveries was that P. rebeli has a species-specific parasitoid that can detect both the M. schencki host ants and P. rebeli larvae by their odour, and itself has a suite of chemicals that can provoke fighting in the host ants (e.g. Thomas and Elmes 1993; Thomas et al. 2002). Recently the stridulations of queens and workers of M. schencki have been recorded and were shown to be similar to the sounds made by P. rebeli caterpillars which respond to the recorded ant sounds (Barbero et al. 2009). In the laboratory Starcke (1949) made quite an important contribution to the morphology of larvae. The chemistry of some glandular secretions of M. schencki workers have been identified (e.g. Evershed et al. 1983; Cammaerts et al. 1982; Attygalle et al. 1983). Workers have been shown to be quite prolific egg-layers while queens regularly lay some trophic eggs (Wardlaw and Elmes 1995, 1998). Mating swarms occur from the end of July to early September, though often slightly earlier than in some sympatric Myrmica species, we have observed mixed swarms and a mating swarm was described by Pontin (1986).

Collingwood (1979) - This is an interesting species somewhat resembling a large paler Myrmica lobicornis but distinguished by the lower more cubical postpetio1e. According to the Danish myrmecologist Chr. Skott, this species differs from other European Myrmica in having no winter brood, is mainly nocturnal and derives much of its food from the glandular excretions of low herbage such as Hypochaeris and Hieracium spp. The entrance to the nest is frequently built up as a collar of vegetable detritus (Bisgaard, 1944). Colonies are single queened and isolated, situated in sandy banks and dry pasture. Alatae are found in August, mating occurring on the ground near the nest.

Nomenclature

 *  schencki. Myrmica rubra var. schencki Viereck, 1903: 72 (w.q.m.) EUROPE (see Baroni Urbani, 1971c: 35 (note)). [First available use of Myrmica rubra subsp. scabrinodis var. schencki Emery, 1895c: 315; unavailable name.] Wheeler, G.C. & Wheeler, J. 1953a: 120 (l.). Subspecies of scabrinodis: Emery, 1908a: 178; Forel, 1915d: 29. Status as species: Bondroit, 1911: 11; Bondroit, 1912: 351; Donisthorpe, 1915c: 265; Bondroit, 1918: 103; Müller, 1923: 44; Finzi, 1926: 109; Karavaiev, 1926b: 95; Stärcke, 1927: 84; Santschi, 1931b: 351; Karavaiev, 1934: 93; Bernard, 1967: 118; Arnol'di, 1970b: 1843; Tarbinsky, 1976: 42; Kutter, 1977c: 70; Arnol'di & Dlussky, 1978: 535; Collingwood, 1979: 56; Seifert, 1988b: 35; Kupyanskaya, 1990: 109; Atanassov & Dlussky, 1992: 99. Senior synonym of kutteri: Bernard, 1967: 118; of subopaca: Arnol'di, 1970b: 1843; of betuliana: Radchenko, 1994f: 77; of schenckioides: Radchenko & Elmes, 2010: 266. See also: Seifert, 2003b: 145; Radchenko, Elmes & Alicata, 2006: 513; Radchenko & Elmes, 2010: 266.
 * kutteri. Myrmica schencki var. kutteri Finzi, 1926: 111 (w.m.) SWITZERLAND. Junior synonym of schencki: Bernard, 1967: 118.
 * subopaca. Myrmica schencki nat. subopaca Arnol'di, 1934: 172, figs. 36, 37 (w.) UKRAINE. [Also described as new by Arnol'di, in Karavaiev, 1934: 96.] [Unresolved junior primary homonym of subopaca Smith, F. 1858b: 127, above.] Junior synonym of schencki: Arnol'di, 1970b: 1843.
 * betuliana. Myrmica betuliana Ruzsky, 1946: 70 (w.) RUSSIA. Junior synonym of schencki: Radchenko, 1994f: 77.
 * schenckioides. Myrmica schenckioides Boer & Noordijk, 2005: 120 figs. 1-4 (q.) NETHERLANDS. Junior synonym of schencki: Radchenko & Elmes, 2010: 266.

Description
Seifert (2003) - Lectotype worker (top specimen, by present designation) and paralectotype worker (bottom specimen on the same pin), labelled by Emery himself "Graten" (?, poorly legible) and "Jl4yrmica scabrinodis var. schencki Emery", MCSN Genova.

Etymology
Radchenko and Elmes (2010) - named for the notable 19th century German myrmecologist, Prof. Carl Friedrich Schenck (1803-1878) of Weilberg, who first recognised this form.