Stenamma sardoum

Seemingly this is a Sardinian endemic, but maybe it occurs also in Corsica (Rigato & Toni, 2011).

Identification
Rigato (2011) - This species has no unique strong diagnostic features, but, besides its distribution, it is recognisable by the following combination of worker characters: the values of SI (usually ≥ 90) and PCI (range: 25–34) plus relatively low and elongate postpetiole and irregular promesonotal sculpturation. The gyne is similar, except for the sculpturation.

At a glance sardoum female castes were easily separated from co-occurring specimens of debile because females of sardoum are mostly ferrugineous, distinctly paler than the brown debile, even though colour differences are generally considered unreliable. Also, in sardoum petiolar and postpetiolar sternites in profile look distinctly, although weakly, more concave below the nodes. In contrast, the waist sternites of Stenamma debile are only faintly concave at most. This difference is easier to appreciate when specimens of both species are compared directly. Stenamma sardoum female castes generally look similar to Stenamma westwoodii. Diagnostic features useful to separate them are difficult to appreciate and rely on difference in PCI, promesonotal sculpturation and shape of postpetiole.

Distribution
Seemingly a relatively common Sardinian endemic. (Rigato 2011)

Distribution based on Regional Taxon Lists
Palaearctic Region: Italy, Malta.

Nomenclature

 *  sardoum. Stenamma sardoum Emery, 1915a: 255, pl. 4, figs. 5, 6 (w.q.) ITALY (Sardinia). See also: DuBois, 1998b: 237; Rigato, 2011: 11.

Emery (1915) described Stenamma sardoum on the basis of a few workers and one gyne, comparing it with Stenamma westwoodii of earlier authors (i.e. specimens now known to be Stenamma debile) and pointed out the strong difference in the shape of the petiolar node that he described as truncate in profile. Actually, Emery was quite wrong in reporting such a feature, even adding a misleading figure. I examined the type series and several other specimens of S. sardoum and all of them have an ordinary, somewhat rounded node in profile with a faint flattening at most. DuBois (1998) designated the lectotype and redescribed S. sardoum. In his keys he stated that the petiolar node was “depressed”. Nevertheless his drawings showed a petiolar profile comparable to that of most Stenamma.

Worker
Rigato (2011) - Lectotype (designated by DuBois (1998)): TL 3.6; HL 0.87; HW 0.72; CI 83; SL 0.66; SI 92; PnW 0.48; AL 1.00; PeL 0.38; PPL 0.26; PeH 0.20; PPH 0.21; PeW 0.16; PPW 0.21; PI1 68; PI2 53; MTL 0.61; TI 85.

Paralectotype: TL 3.6–3.9; HL 0.86–0.91; HW 0.72–0.77; CI 84–85; SL 0.67–0.70; SI 89–93; PnW 0.48–0.51; AL 1.04–1.10; PeL 0.38–0.42; PPL 0.26–0.29; PeH 0.20–0.23; PPH  0.21–0.23; PeW 0.15–0.18; PPW 0.20–0.23; PI1 68–69; PI2 53–55; MTL 0.61–0.65;  TI 84–86 (3 measured).

TL 3.3–4.3; HL 0.81–0.91; HW 0.67–0.76; CI 82–85; SL 0.63–0.70; SI 89–96;  PCI  25–34;  PnW 0.43–0.51; AL 0.95–1.11; PSI 1.58–1.88; PeL 0.37–0.42; PPL 0.23–0.27; PeH  0.19–0.22; PPH 0.18–0.22; PeW 0.15–0.17; PPW 0.19–0.23; PI1 62–69; PI2 51–57; MTL 0.56–0.65; TI 81–89 (17 measured).

Queen
Rigato (2011) - Paralectotype: TL 4.5; HL 0.95; HW 0.82; CI 86; SL 0.74; SI 90; ScW 0.64; MnL 1.01; PeL 0.48; PPL 0.33; PeH 0.25; PPH 0.26; PeW 0.20; PPW 0.28; PI1 69; PI2 59; MTL 0.72; TI 88.

TL 4.4–5.0; HL 0.92–1.01; HW 0.79–0.85; CI 84–86; SL 0.71–0.76; SI 89–90; PCI 30–34; AL 1.28–1.40; PSI 1.60–2.10; ScW 0.64–0.68; MnL 0.92–1.01; PeL 0.47–0.50; PPL 0.31–0.33; PeH 0.25; PPH 0.24–0.26; PeW 0.20–0.21; PPW 0.26–0.28; PI1 66; PI2 59; MTL 0.66–0.73; TI 84–86 (2 measured).

Type Material
Rigato (2011) - Lectotype worker,  paralectotype  workers  and  gyne, ITALY: SARDINIA, Aritzo,  xi.1911  (D. Dodero)  [examined].

Determination Clarifications
Rigato (2011) - X. Espadaler (pers. comm.) has assigned the single specimen reported from Spain by Collingwood and Yarrow (1969) to Stenamma debile.

References based on Global Ant Biodiversity Informatics

 * Bernard F. 1967. Faune de l'Europe et du Bassin Méditerranéen. 3. Les fourmis (Hymenoptera Formicidae) d'Europe occidentale et septentrionale. Paris: Masson, 411 pp.
 * Borowiec L. 2014. Catalogue of ants of Europe, the Mediterranean Basin and adjacent regions (Hymenoptera: Formicidae). Genus (Wroclaw) 25(1-2): 1-340.
 * Branstetter M. G. 2012. Origin and diversification of the cryptic ant genus Stenamma Westwood (Hymenoptera: Formicidae), inferred from multilocus molecular data, biogeography and natural history. Systematic Entomology 37: 478-496.
 * DuBois, M. B. "A revision of the ant genus Stenamma in the Palaeartic and Oriental regions." Sociobiology 32 (1998): 193-403.
 * Emery C. 1916. Fauna entomologica italiana. I. Hymenoptera.-Formicidae. Bullettino della Società Entomologica Italiana 47: 79-275.
 * Grandi G. 1935. Contributi alla conoscenza degli Imenotteri Aculeati. XV. Boll. R. Ist. Entomol. Univ. Studi Bologna 8: 27-121.
 * Liu X., and Z. H. Xu. 2011. Three New Species of the Ant Genus Stenamma (Hymenoptera: Formicidae) from Himalaya and the Hengduan Mountains With a Revised Key to the Known Species of the Palaearctic and Oriental Regions. Sociobiology 58: 733-748.
 * Poldi B., M. Mei, and F. Rigato. 1995. Hymenoptera, Formicidae. Vol 102. Checklist delle specie della fauna Italiana: 1-10.
 * Rigato F. 2011. Contributions to the taxonomy of West European and North African Stenamma of the westwoodii species-group. (Hymenoptera Formicidae). Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 37: 1-56.
 * Rigato S., and I. Toni. 2011. Short notes 21. Hymenoptera, Formicidae. Pp. 873-882 in: Nardi, G.; Whitmore, D.; Bardiani, M.; Birtele, D.; Mason, F.; Spada, L.; Cerretti, P. (eds.) 2011. Biodiversity of Marganai and Montimannu (Sardinia). Research in the framework of the ICP Forests network. Conservazione Habitat Invertebrati, 5. Sommacampagna, Verona: Cierre Edizioni, 896 pp.