Formica exsecta

This is an active aggressive species building mounds of leaf litter in open woodland, moorland and rough pasture. On disturbance the ants swarm out and bite vigorously. Nests may contain a thousand or more workers. F. exsecta is mainly aphidicolous tending aphids on Juniperus, Picea and other trees but is also predaceous. Colonies extend by nest splitting but single queens also start colonies by securing acceptance in nests of Formica lemani or Formica fusca. Alatas occur in July (Collingwood 1979).

Identification
Bicoloured with gaster dark brown, rest of body reddish with varying amount of dark colour on head and promesonotum. Head strongly excised posteriorly; maxillary palps 6 segmented, long as half head length. Scale strongly emarginate. Eyes with very distinct erect hairs which are normally abundant. Body pilosity variable - erect hairs on all gaster tergites, on clypeus and on dorsum of head, sometimes also on occipital margins. Clypeus not impressed. Length: 4.5-7.5 mm (Collingwood 1979).

Seifert (2000) - Interspecific setae and pubescence differences between Coptoformica species are normally correlated with differences in body measures and indices at least in the queens. Investigations of the enormous setal and pubescence variability of the exsecta samples seen during this study could not convincingly show such correlations and could not satisfactorily separate entities of possible taxonomic significance. The same local population may show a wide range of pubescence and pilosity variance and there is no clear indication that certain setae morphs could be associated with a certain distribution, habitat selection, or biology. As a consequence and in agreement with the view of Agosti (1989), Formica exsecta is considered here as polymorphic, relatively eurytopic species with a large range, similar to the situation in Formica truncorum, Formica pratensis, and Scandinavian Formica lugubris. This conception of F. exsecta contrasts the situation in the other Coptoformica species that are constant, monomorphic entities with a defined zoogeography and more specific habitat selection. Males: Eyes with numerous long hairs; EyeHL 35-50 μm. Clypeus with numerous setae; ClySet 2-5. Mesosoma with numerous standing setae. Craniad profile of forecoxae with standing setae.

Distribution
Seifert (2000) - South to Central Spain, to the N Appennine and to the Balkans at 40°N. Found in high Anatolia and Caucasus; apparently absent from the driest Pontic and Caspian steppe zones. West to SW England and the Scottish Highlands. Northern range troughout Fennoscandia up to North Cape. Distribution in the east in European Russia, across Siberia, Mongolia, NE China (Beishan National Park, 37°N, 102°E) and east to the lower Amur river. The northern distribution in the continental parts of Eurasia is limited by the -8 °C isotherm of soil in a depth of one meter (achieved at 67°N in W Siberia at the Ob river and at 62°N in E Siberia at the Lena river) and the southern distribution coincides with the southern border of foreststeppe (Dlussky 1967). Vertical distribution: in Switzerland and Austria 300-2250 m, bimodal, with very low frequencies from 800-1200 m; Bulgarian mountains 1100-2200 m.

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

Habitat
Seifert (2000) - F. exsecta is more a generalist with a wider habitat selection than usual within Coptoformica species. Very different open or slightly shaded habitats, which must have medium-term stability at least, are inhabited. A high cover percentage of grasses within the field layer is typical but not essential. As for all species of the group, sites with rapid plant succession, with high nitrogen input, or sites within the inundation plains of rivers are not colonised. Formica exsecta and all other members of the group cannot increase nest temperatures by metabolic heat production independent of environmental temperatures as known for populous nests of some wood ant species. The dependence of Coptoformica upon direct insolation is thus increased and nests cannot be constructed in fully shaded woodland habitats. Habitat types used by exsecta are subalpine and boreomontane pastures, clearings and margins of woodland, sunny forests, semidry to xerothermous grasslands, heathland, and dryer spots of bogs and fens.

Biology
Seifert (2000):

Status as threatened species
Red List Germany: three (threatened). In Central Europe it is probably the least endangered Coptoformica species though its populations have significantly declined since 1950. The decline is caused by afforestation of clearings and meadows, vanishing of coppice wood management, decline of sheep pasturing, intensifying of cattle pasturing, intensive use of mineral fertilisers and liquid manure, and high athmospheric nitrogen immission. Dewes (1993) recorded F. exsecta colonies in the Nature Park Saar-Hunsrück preferentially in sites of historic coppice wood management where oak bark for tanneries was harvested.

Colony foundation
Flight or ground dispersal of single queens is followed by socially parasitic colony foundation in nests of the subgenus Serviformica. Formica fusca (Dlussky, Collingwood, Pisarski, Agosti, Seifert) and Formica lemani (Collingwood, Agosti, Hellrigl, Seifert) are reported as host species. According to Pisarski (1982), socially parasitic colony foundation is only possible in queenless host nests. The same author stated that monogynous nests of exsecta never accept alien queens, with exception of very minute nests. To become polygynous, they must have lost the queen and can then adopt several queens simultaneously. Once shifted to polygyny, huge polycalic colony systems may develop by nest splitting.

Nest construction
Nest mounds are often more structured than in related species. Materials and type of nest construction depend upon insolation, ground water level, soil type, and composition of vegetation. The following type is frequent on mineralic soils: a calotte-like outer hull of the dome, which can often be lifted without breaking (Agosti 1989), is constructed with more dense, strongly adhesive materials (usually finely cut grass pieces). Rather voluminous upper brood chambers (during warm weather the sites for pupae) may be situated between this hull and inner mound material that consists of more lofty plant pieces. The lower mound core is a mixture of humified plant material and mineralic soil. Galleries may reach 150 cm down into the soil. In polygyous nests and during summer, numerous clearly separated chambers of 2 cm width are found below the level of soil surface down to 80 cm. These chambers usually contain a queen, eggs, small larvae, and few workers. In habitats deficient of grasses, other materials as coniferous needles, rabbit pellets, or small pebbles may be used. Nest diameters may reach 200 or even 300 cm (Agosti 1989; Dlussky 1967). In semi-shaded boreal forests, the author observed nest mounds of 150 cm height and 180 cm diameter, the base of which had been abandoned by the ants and covered by mosses (Polytrichum).

Development and microclimatic requirements
Alates develop from eggs laid in early spring. Oviposition starts in Central European lowland habitats in late March but is considerably delayed with growing altitude and latitude. In Finnish monogynous colonies, less than 5% of the spring eggs develop to workers (Chapuisat et al. 1997), but this ratio may reach 50% in Swiss polygynous societies (Schneider pers. comm.). The main source of worker production is late spring or summer eggs. The optimum temperature for “brood development” is 28-30 °C (Grinfeld 1939, cited in Dlussky 1967). The supercooling point of winter-adapted Siberian workers is -20 °C; the long-term minimum at which 50% of workers survive is -8 °C (Berman, Shigulskaja & Leirich 1987; Leirich 1989). The conditions where soil temperatures in a depth of one metre do not decline below -8 °C are given in E Siberia up to 62°N, which coincides with the northern distributional border of exsecta.

Demography of nests and colonies
The ratio of monogynous nests vs polygynous/polycalic colonies differs locally and geographically. Patchiness and general availability of suitable habitats and a payoff between the costs of single queen colony foundation and the costs of reproductive competition in polygynous nests are probable factors influencing this ratio. In S Finland monogyny/monodomy clearly predominates. Big polycalic colonies are known from the Alps, Central Europe, and European Russia. The mean longevity of queens in monogynous nests in S Finland was over 20 years (Pamilo 1991). According to Sundström et al. (1996), 39% of the queens in 57 monogynous S Finnish nests were multiply-mated (polyandrous). The sex ratio of produced alates is strongly dependent upon the number of queens in a colony and the number of mates per queen; in highly polycalic colonies in the Swiss Alps it was about 15:1 (Schneider pers comm.), in Finnish polyandrous/monogynous colonies it was 3.76:1, but in Finnish monoandrous/monogynous nests it was 1 : 2.2. Workers of the latter colonies increased their inclusive fitness by selectively killing male larvae before pupation and (most probably) feeding them to the now rapidly growing female larvae. Ecological and demographic factors (recource limitation!) are believed to interfere with genetic factors (optimisation of kinship value), i.e. males should survive in higher numbers in monoandrous/monogynous nests if there is plenty of recources (Chapuisat et al. 1997). Monogynous nests mainly produce the large male morph (macraner) but polycalic colonies mainly micraners (Pamilo & Rosengren 1984). The micraners can develop from worker-laid eggs, mature later, and show narrower activity peaks. Both micraners and macraners are normally haploid (Agosti 1989). No complete population census has been performed so far in exsecta. The “Aussendienst” population of four monogynous nests of 368 ± 100 cm2 basal area was censused by Pisarski (1982) as 2750 ± 1000 workers, i.e. 7.5 workers/cm2 basal nest area. That means a total population of 18.8 workers/cm2 basal nest area if assuming 40% Aussendienst workers. The total population of exactly censused polygynous bruni nests was 39.3 workers/cm2 basal nest area (Schneider pers. comm.). Both values seem realistic in view of the higher worker density and smaller worker size in polygynous nests. A very large polygynous exsecta nest of 150 cm diameter should then contain > 300 000 workers. Polycalic exsecta colonies may be huge and can dominate a site as known for Formica polyctena. Dewes (1993) described a supercolony comprising 408 nests (the smallest not counted!) spreading over an area of 2 ha. If assuming only 25 000 workers for an average polygynous exsecta nest, the whole population of this colony should be > 10,000,000.

Swarming
Mature alates are found in the nest 28.2 July ± 20.2 d (10 June-4 Sept, n = 33). In contrast to R. Rosengren, M. A. Schneider did not observe micraners to fly higher and farther than macraners. In Swiss polycalic colonies about 30% of females fly, the others are inseminated at the nest mounds. Swarming is restricted to the the first half of the day (between 5.30 and 12.20 h) and starts as soon as the first direct sunlight hits the mound surface. Completely cloudy sky or strong air movement prevents the flight and beginning sunshine in the second half of the day can not release it (Schneider pers. comm., and my own observations).

Food sources
F. exsecta can use a wide range of food sources. Trophobiosis with epigaeic and subterranean Aphidina (and more rarely Cicadina and Coccina) is observed and obviously covers a major portion of the energy needs. Lachnidae are the main trophobionts in coniferous and deciduous forests. Zoophagy may be important and is then comparable to that of Formica polyctena with the difference of a smaller average size of prey items (Wesselinov & Horstmann 1968); all kinds of dead or living Arthropoda and Lumbricidae are consumed. Very populous supercolonies effectively displace different species of predatory arthropods from their territory.

Intraspecific behaviour
Monogynous colonies are highly aggressive against conspecific aliens. Polygynous/monodomous colonies show reduced aggressivity but only polycalic colonies do not establish territorial boundaries against other conspecific polycalic colonies (Pisarski 1982).

Nomenclature

 *  exsecta. Formica exsecta Nylander, 1846a: 909, pl. 18, fig. 20 (w.q.m.) FINLAND. Combination in F. (Coptoformica): Müller, 1923: 146. Senior synonym of dalcqi, etrusca: Bernard, 1967: 323; of exsectopressilabris: Bernard, 1967: 323; Dlussky & Pisarski, 1971: 194; of kontuniemii, sudetica, wheeleri Stitz: Dlussky, 1967a: 100; Dlussky & Pisarski, 1971: 194; of rubens: Dlussky, 1964: 1027; of nemoralis: Seifert, 2000a: 526. See also: Donisthorpe, 1915d: 273; Parapura, 1972: 763; Kutter, 1977c: 283; Agosti & Hauschteck-Jungen, 1988: 280; Kupyanskaya, 1990: 200; Atanassov & Dlussky, 1992: 282; Seifert, 2000a: 525; Radchenko, 2007: 36.
 * exsectopressilabris. Formica exsecta var. exsectopressilabris Forel, 1874: 52 (w.q.m.) SWITZERLAND. Subspecies of pressilabris: Dalla Torre, 1893: 205. Raised to species: Bondroit, 1912: 352; Bondroit, 1918: 63. Subspecies of exsecta: Karavaiev, 1927c: 284; Karavaiev, 1936: 255; Boven, 1947: 189. Junior synonym of exsecta: Bernard, 1967: 323; Dlussky & Pisarski, 1971: 194.
 * rubens. Formica exsecta var. rubens Forel, 1874: 51 (w.) SWITZERLAND. Raised to species: Bondroit, 1918: 62. Subspecies of exsecta: Ruzsky, 1925b: 43; Emery, 1925b: 257. Junior synonym of exsecta: Dlussky, 1964: 1027.
 * etrusca. Formica exsecta var. etrusca Emery, 1909b: 191, fig. 5 (w.) ITALY. Raised to species: Bondroit, 1918: 64. Subspecies of exsecta: Emery, 1925b: 257; Karavaiev, 1926e: 196. Junior synonym of exsecta: Bernard, 1967: 323.
 * dalcqi. Formica dalcqi Bondroit, 1918: 63 (w.) FRANCE. Subspecies of exsecta: Emery, 1925b: 257. Junior synonym of exsecta: Bernard, 1967: 323.
 * sudetica. Formica exsecta var. sudetica Scholz, 1924: 48 (w.) POLAND. Junior synonym of exsecta: Dlussky & Pisarski, 1971: 194.
 * kontuniemii. Formica kontuniemii Betrem, 1954: 230 (w.) FINLAND. Junior synonym of exsecta: Dlussky, 1967a: 100; Dlussky & Pisarski, 1971: 194.
 * nemoralis. Formica nemoralis Dlussky, 1964: 1037 (w.m.) UKRAINE. Junior synonym of forsslundi: Dlussky, 1967a: 105; of exsecta: Seifert, 2000a: 526.

Worker
Seifert (2000) - Maximum size larger than in other species (CL 1419 ± 82, 1200-1641; CW 1362 ± 83, 1131-1574). Head shape of average Coptoformica type (CL/CW 1.042 ± 0.023, 0.979-1.099); however, long-headed and short-headed specimens may occur within the same nest. Rather long scape (SL/CL 1.008 ± 0.022, 0.931-1.063). Clypeus at least in anterior third, but normally also in median and posterior portions with standing setae (ClySet 3.54 ± 1.08, 2-5). Lateral semierect setae in the ocellar triangle usually present (OceSet 92%). Eye hairs at least in a fraction of the nest population strongly developed, often hook-shaped (EyeHL 27.0 ± 6.5, 0-45; Fig. 10). Pubescence in the occellar triangle frequently dilute, but enormous intraspecific and intranidal variation occurs (sqrtPDF 5.69 ± 0.90, 3.78-9.30). Region of occipital corners with semierect to subdecumbent pubescence (however, in specimens of the etrusca population almost appressed). Craniad profile of forecoxae with semierect setae (nCOXA 8.86 ± 3.89, 0.5-23). Dorsal mesosoma and propodeum occasionally with few standing setae, lateral metapleuron and ventrolateral propodeum more frequently setaceous (nMET 1.86 ± 2.11, 0-9). Outer edge of the hind tibial flexor side conspicuously hairy (nHTFL 10.97 ± 2.82, 5.0-23.0), with two size classes of setae, and subdecumbent pubescence (Fig. 2). Semierect setae on gaster tergites as a rule beginning on the 1st tergite (TERG 1.19 ± 0.46, 1-3); nest sample means of TERG always < 2.4. Pubescence density on first gaster tergite with extreme intranidal and intraspecific variation (sqrtPDG 6.82 ± 1.19, 3.93-9.88).

Queen
Seifert (2000) - Size definitely larger than in other species (CL 1636 ± 44, 1514-1741; CW 1721 ± 42, 1629-1809; ML 2878 ± 116, 2613-3115). Head broad (CL/CW 0.950 ± 0.022, 0.900-1.008), scape long (SL/CL 0.956 ± 0.023, 0.893-1.004). Clypeus at least in anterior third, but normally also in median and posterior portions with standing setae. Lateral semierect setae in the ocellar triangle normally present. Eye hairs normally long and numerous, often hook-shaped (EyeHL 45.6 ± 7.6, 31-69); samples with less numerous eye hairs may occur. Pubescence in the occellar triangle relatively dense (sqrtPDF 4.28 ± 0.49, 3.34-5.75), less variable than in workers. Occipital corners of head normally with semierect smaller setae and pubescence, morphs with almost reduced and such with very developed occipital hairs may occur (OccHD 46.9 ± 22.5, 7-107). Brilliance of dorsal head surface variable, but relatively matt and weakly sculptured surfaces dominate (GLANZ 1.71 ± 0.36, 1.0-2.5). Craniad profile of forecoxae with semierect setae (nCOXA 12.95 ± 4.09, 3.5-23.0). Promesonotum normally with standing setae that clearly differ from semierect pubescence, in weakly haired specimens the differentiation between shorter semierect setae and longer semierect pubescence can be lost (MnHL 181.8 ± 40.0, 0-256). Outer edge of the hind tibial flexor side conspicuously hairy (nHTFL 12.81 ± 3.20, 8.0-22.0), with two size classes of setae and subdecumbent pubescence. Semierect setae on gaster tergites always beginning on the first tergite (TERG 1.00 ± 0.00). Pubescence density on first gaster tergite with extreme intraspecific variation (sqrtPDG 6.17 ± 1.16, 3.83-9.25).

Type Material
Helsinki, Finland. Syntypes 1 male, 1 female, 3 workers [investigated].