Formica frontalis SANTSCHI, 1919

Seifert, Bernhard, 2021, A taxonomic revision of the Palaearctic members of the Formica rufa group (Hymenoptera: Formicidae) - the famous mound-building red wood ants, Myrmecological News 31, pp. 133-179 : 171-172

Formica frontalis SANTSCHI, 1919

Formica truncorum var. frontalis SANTSCHI, 1919 [type investigation]

Investigated was the lectotype worker (by present designation), labelled in Santschi’s handwriting “ Formica truncorum F. v. frontalis type Sants”, “ Espagne Pozuelo de Calatrava (de la Fuente)”; depository NHM Basel. The original description reports as type locality nothing but “ Pozuelo de Calatrava (De la Fuente)”. Accordingly, a worker specimen depicted in AntWeb ( ANTWEB 2021 ) under CASENT0912253, labelled “SIERRA DE QUADAR- RAMA Dusmet” and “type” has no type status.

All material examined. Numeric phenotypical data were recorded in 11 samples with 26 workers and six gynes from Spain. For details, see SI1, SI2, and SI3.

Geographical range. According to TINAUT & MARTINEZ-IBANEZ (1998) and ESPADALER & GOMEZ (2000) rather homogenously distributed over entire Iberia with the altitude of 15 sites being 1160 ± 450 m, which is lower than in Formica dusmeti .

Diagnosis of worker ( Tab. 5, key). Medium-sized, mean and maximum CS over all morphological and social phenotypes 1792 and 2045 µm. Head moderately elongated, CL / CW 1750 1.102. Clypeal morphology as in Formica truncorum . Scape long and slender, SL / CS 1750 0.993, SL / Smax 1750 10.60. Petiole scale narrow, PeW / CS 1750 0.450. Eyes without or with short microsetae, EyeHL 1750 16 µm. Dorsal plane of scape without or with only single setae, nSc 1750 0.7. Setae number on each place of the body smaller than in F. truncorum but setae length equal or even larger, nCH 1750 14.5, nGu 1750 19.5, nPn 1750 59.5, nMes 1750 26.1, nPr 1750 29.2, nMet 1750 10.2, OccHL 1750 114 µm, GuHL 1750 204 µm, mPnHL 1750 97µm, MetHL 1750 161 µm. Dorsal surface of head usually without the deep and broad microfoveolae characteristic for F. truncorum . Pigmentation as in the latter.

Diagnosis of gyne ( Tab. 8). Only specimens from a single supercolony were available. These were much larger than Formica truncorum gynes of the polygynous to supercolonial social form, CS 2106 µm. Head capsule in dorsal view less trapezoidal than in F. truncorum , clypeal shape as in that species. Scape rather long and slender, SL / CS 0.872, SL / Smax 9.30. Petiole wider than in F. truncorum , PeW / CS 0.686. Setae on eyes short, EyeHL 31 µm. Setae on dorsum of scape usually absent, nSc 0.2. Setae on remaining parts of body present, less numerous than in F. truncorum but of similar length, nCH 23.4, OccHL 202µm, nGu 34.8, GuHL 287µm, PnHL 255 µm, nMet 26.3, MetHL 252µm, nPe 10.8. Dorsum of first gaster tergite moderately shiny, with dense transverse microripples and dilute pubescence (sqPDG 12.25µm), microfoveolae often absent. Pigmentation as in F. truncorum .

Taxonomic comments and clustering results. The geographic ranges of Formica frontalis and Formica truncorum are disjunct, and the morphological distinctness of the two species is strong enough to consider them as heterospecific. The eleven Iberian nest samples of F. frontalis can be separated from 37 Panpalaearctic nest samples of F. truncorum using the characters SL / CS 1750, PeW / CS 1750, EyeHL 1750, nCH 1750, nMet 1750, and MetHL 1750 ( Fig. 34 ). The classification error by an LDA was 4.2% in 118 worker specimens. It is worth mentioning that gynes from highly polygynous or supercolonial F. truncorum populations have a much smaller size than the investigated gynes from the F. frontalis supercolony at Puerto de Navacerrado (SaNo. 149 and 150), which provides additional support for heterospecificity.

Biology. Compared with Formica dusmeti, TINAUT & MARTINEZ-IBANEZ (1998) reported a more frequent occurrence in Quercus than in conifer forests, which is probably not due to a preference of broad-leafed woodland but rather a consequence of the lower altitudinal range. The species is also found in open treeless habitats with low shrubs. Nest construction is similar to Formica truncorum , not showing the large regular mounds seen in the Formica rufa species complex. The above-ground part is usually a rather flat accumulation of plant material, or the nests are completely under stones around which some plant material is deposited.

Figures

Fig.34: Nest-sample means of a linear discriminant analysis and principal component analysis of workers of Formica frontalis (black rhombs) and Formica truncorum (white dots).Six phenotypic characters were considered.