Formica stitzi STITZ, 1939

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 : 169-170

Formica stitzi STITZ, 1939

Formica truncorum var. stitzi STITZ, 1939 [description and zoogeography]

This taxon was described from near Eberswalde ( Germany) under the unavailable name Formica rufa ssp. truncicola var. stitzi KRAUSSE, 1926 . Types are unknown. Within the four species known to occur in the vicinity of Eberswalde, the description matches the situation in F. truncorum .

All material examined. Numeric phenotypical data were recorded in 50 samples with 92 workers and in 22 gynes. These originated from Belarus (one sample), China (seven), Czechia (one), Denmark (one), Finland (two), France (three), Germany (12), Japan (two), Kazakhstan (seven), Kyrgyzstan (11), Norway (one), Russia (two), and Ukraine (one). For details, see SI1, SI2, and SI3. The total of samples investigated either numerically or subjectively was 136.

Geographical range. Eurosiberian , temperate to boreal; from Netherlands and E France (5° E) to Yakutsk at least (62° N, 130° E). In NE China, the Ussuri region , Sakhalin, Hokkaido, the northern half of Honshu, and the Western Kurils (148° E), it is replaced by the weakly deviating East Asian population. The southern and northern distributional limits in Europe are 42° N ( Bulgaria) and 71° N ( North Cape ). These are in Central Siberia, along the 100 th degree of longitude, 46° N and 67° N. In Europe occurring from the planar to montane zone, in the Alps ascending to 1800m. Rare in the Crimea and Caucasus ( DLUSSKY 1967). A population isolated from the Eurosiberian one is found in the Central Asian mountains – in Dzungarian Alatau, Tian Shan (here at 43° N up to 2700 m), and Pamir south to Karakoram (35° N).

Diagnosis of worker ( Tab. 5, Fig. 18 , key). Polymorphic, with regional differences shown in Table 5. Medium-sized, mean and maximum CS over all morphological and social phenotypes 1754 and 2177µm. Head moderately elongated, CL / CW 1750 1.099. Middle part of lateral clypeus more deeply depressed than in the Formica rufa species complex, anterolateral clypeus as a result forming a bead; median clypeal carina blunt or absent. Scape long and very slender, SL / CS 1750 0.985, SL / Smax 1750 10.87. Second and third segment of antennal funiculus more slender than in the species treated above, IF2 2.15 ± 0.09 (n = 70). Petiole scale narrow, PeW / CS 1750 0.442. Eyes always with microsetae, EyeHL 1750 40 µm. Dorsal plane of scape usually with more setae than in other species, nSc 1750 10.3. Except for the Hippie-morph of Formica lugubris , setae number on each place of the body larger than in any species of the F. rufa group, nCH 1750 42.5, nGu 1750 40.5, nPn 1750 81.6, nMes 1750 35.8, nPr 1750 46.5, nMet 1750 17.6. Hind margin of head usually with very long setae, but setae length on other body parts lower than in the most hairy morphs of Formica pratensis and F. lugubris , OccHL 1750 136µm, GuHL 1750 187µm, mPnHL 1750 91 µm, MetHL 1750 142 µm. Dorsum of head, in addition to the other elements of microsculpture, with deeper and broader microfoveolae which are usually the base of setae. Typical pigmentation in medium-sized to large workers: whole head, mesosoma, petiole, and frontal part of first gaster segment light orange brown; dark brown or blackish brown patches on vertex and dorsal mesosoma may occur in some samples.

Diagnosis of gyne ( Tab. 8, Fig. 19 , key). On average rather small but extremely size-polymorphic; minimum, mean, and maximum CS over all social phenotypes 1737, 2002, and 2256 µm. Head capsule in dorsal view appears trapezoidal, with more or less linear, frontad converging sides. Middle part of lateral clypeus more deeply depressed than in the Formica rufa species complex, anterolateral clypeus as a result forming a bead; median clypeal carina absent. Scape long and slender, SL / CS 0.903, SL / Smax 9.63. Petiole scale relatively narrow, PeW / CS 0.597. Setae on whole body very numerous, very thin, and usually very long. EyeHL 95 µm, nSc 28.0, nCH 62.6, OccHL 215µm, nGu 65.1, GuHL 267µm, PnHL 242 µm, nMet 38.0, MetHL 249 µm, nPe 15.0. Dorsum of first gaster tergite moderately shiny, with dense transverse microripples, rather dilute pubescence (sqPDG 9.76 µm), and rather large, deep, and widely spaced microfoveolae. The latter may be occasionally absent. Light reddish pigmentation component on all body surfaces more developed than in the F. rufa species complex.

Taxonomic comments and clustering results. Formica truncorum , as any species of the F. truncorum species complex, is rarely confused with other species of the Formica rufa group. Occasional confusion with Formica pratensis is possible due to high similarity in pilosity data and most of the body shape data and due to variation in pigmentation in both species. However, the separation by exploratory and hypothesis-driven data analyses shows an error <1% on the nest sample level in material from the whole Palaearctic range. Furthermore, the shape of clypeus and funiculus segments is usually diagnostic. In gynes, the separation from any species of the F. rufa species complex is also clear in both exploratory and hypothesis-driven data analyses. Less hirsute specimens from Kyrgyzstan, formerly identified as „ Formica cf. frontalis “ ( SCHULTZ & al. 2006), were re-classified in this study as F. truncorum . The current data give no indication that F. frontalis does occur outside of Iberia.

The Panpalaearctic population of Formica truncorum cannot reasonably be subdivided into clusters of separate taxonomic identity based on the morphological data available at present. On worker individual level, the West and Central Palaearctic population differs from the East Palearctic one by smaller SL / CS 1750, nPn 1750, and nMet 1750 ( Tab.5; ANOVA F 1,90> 15, p <0.001). Yet, it was not possible by any tested exploratory data analysis to cluster the East Palaearctic population separately – neither on individual nor on nest sample level. As a consequence, Formica yessensis WHEELER, 1913 and Formica approximans WHEELER, 1933 are synonymized here with F. truncorum . A subdivision within the East Palearctic population is also not possible. Using nuDNA (microsatellites), IMAI & al. (2016) investigated the Japanese-Korean population. They could not show genetic differences between populations they had pre-determined as “ F. yessensis ” and “ F. truncorum ” based on subjective assessment of setae numbers on hind tibia. IMAI & al. (2016) reported a “robust” genetic indication for the presence of only a single Japanese-Korean population and a “fragile” morphological classification. For separation from Formica frontalis and Formica sinensis , see section “ Formica frontalis SANTSCHI, 1919 ” (p. 171) and “ Formica sinensis WHEELER, 1913 ” (p. 172).

Biology. See the species profile given by SEIFERT (2018). Gyne size polymorphism with large disperser gynes having more fat and glycogen and larger flight muscles than smaller inbreeding gynes is more strongly expressed in Formica truncorum than in any other species of the Formica rufa group.

Figures

Figs.14-20: (14-lugu) Formica lugubris, worker, normal morph, head; central vertex suggestedly shiny due to weaker transverse microsculpture. (15-lugu) Formica lugubris, worker, Hippie morph, head; central vertex suggestedly shiny due to weaker transverse microsculpture. (16-helv) Formica helvetica sp.n., worker, holotype, head. (17-helv) Formica helvetica sp.n., worker, holotype, lateral. (18-trun) Formica truncorum, worker, head. (19-trun) Formica truncorum, gyne, head. (20-sine) Formica sinensis, worker, lateral; note the contrast between weak pronotal and strong gular pilosity.