Stenamma westwoodii

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Stenamma westwoodii
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Stenammini
Genus: Stenamma
Species: S. westwoodii
Binomial name
Stenamma westwoodii
Westwood, 1839

Rigato 2011 Stenamma westwoodii wp2.jpg

Rigato 2011 Stenamma westwoodii wd.jpg


At a Glance • Polygynous  

 

Identification

Pale to dark rusty red; petiole a simple node with rounded dorsal area, propodeal spines short. Head longitudinally striate in front, alitrunk and back of head with weak reticulate sculpture. Body with erect scattered pale hairs, sparse and decumbent on appendages. Length: 3.5-4.0 mm (Collingwood 1979).

Rigato (2011) - A species with moderately elongate scapes and legs, recognizable in female castes especially by its slightly constricted posterior clypeal lobe, whose minimum width is about 1/5 to almost 1/4 of the maximum distance between the frontal lobes. Also, worker’s promesonotum has a well defined, but wandering, median carina, which is crossed by short irregular transverse rugulae. The male has fully developed, 6-toothed, mandibles and smooth and shining propodeal dorsum.

I saw relatively few specimens of genuine Stenamma westwoodii. Among the distinctive features pointed out by DuBois (1993) the narrow posterior clypeal portion and the “leggy appearance” of female castes are useful; however, the latter is shared with other species. Although I consider DuBois measurements quite inaccurate as regards the posterior clypeus, S. westwoodii does show a slightly different shape of the latter, which is narrower than in related taxa. In most Stenamma the posterior clypeal lobe is somewhat parallel-sided between the frontal lobes; whereas in S. westwoodii it is slightly narrower in front than behind forming a sort of “neck”. As Seifert (2007) more carefully stated in his keys, in S. westwoodii that portion is as narrow as about 1/6 of the maximum distance between the frontal lobes at the level of antennal insertions. In S. debile, and other species, that ratio is about 1/4 to 1/3. My measurements show a ratio (expressed as a percentage, PCI) of about 1/5 to nearly 1/4 for S. westwoodii.

DuBois (l.c.) defined S. westwoodii as more “leggy” because the species has longer appendages than Stenamma debile. This feature makes S. westwoodii closer to Stenamma sardoum and to Stenamma africanum. Also, all of these three species share other features: 1) in workers the main sculpture of pronotum, especially laterally, is more or less irregularly reticulate-rugulose rather than prevailingly longitudinally rugulose; and 2) the petiole in profile has a more pronounced concavity below the node and looks somewhat more slender. In addition, I realized that S. westwoodii seems more closely related to S. sardoum. Besides evident differences in PCI, other seemingly important characters concern the sculpturation of promesonotum and the PPH. In S. westwoodii the promesonotum has a median irregular, but easily identifiable, carina which is mostly crossed by several transverse irregular rugulae and the dorsum looks quite loosely areolate. In S. sardoum the median carina is less evident and the remaining sculpturation is even more irregular.

Moreover, S. westwoodii has a relatively higher postpetiole, which looks less elongate than in S. sardoum.

DuBois (1993) pointed out that in dorsal view the petioles of westwoodii and debile are different. As mentioned above, in the comments on debile, I tried such a comparison and found that in westwoodii (as well as in sardoum, and msilanum) the petiole in dorsal view is more parallel sided than in S. debile, whose petiole is more distinctly narrower anteriorly. Also, the male of S. westwoodii is distinctly different from that of debile, as already reported by DuBois (1993).

Finally, I also assign to this taxon a single worker labeled: Foix Ariege (Gallia) [=FRANCE], 1/15.VI.1914, leg. A. Dodero. It is indistinguishable from British westwoodii specimens, including the promesonotal sculpturation; but its gaster has the first tergite finely and superficially reticulate-punctate on most of its surface. I found a similar sculpture in a worker from UK, and therefore I would presume the occurrence of such sculpture to be normal variation and relatively widespread in this species.

Keys including this Species

Distribution

South United Kingdom, Belgium, the Netherlands (Seifert, 2007) and Southwest France. (Rigato 2011)

South and Central Europe from Spain to Caucasus and Italy to South Scandinavia (Collingwood 1979).

Distribution based on Regional Taxon Lists

Palaearctic Region: Armenia, Belgium, Denmark, Georgia, Germany, Spain, Sweden, Ukraine, United Kingdom of Great Britain and Northern Ireland (type locality).


Distribution based on AntMaps

AntMapLegend.png

Distribution based on AntWeb specimens

Check data from AntWeb

Biology

This is an unobtrusive species often taken as solitary workers in woodland. Nests consists of up to 150 workers with a single queen. They may be found in dry well drained woodland under deep stones or among tree roots and under moss. Workers forage during early morning or on dull warm days. This species is partly scavenging and partly predatory on small insects and mites but is slow moving and non-aggressive towards other ant species. Alatae are found in the nests from August to late autumn and have been taken on the wing during September and October.

Castes

Worker

Queen

Male

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • westwoodii. Stenamma westwoodii Westwood, 1839: 219, fig. 86 (m.) GREAT BRITAIN. Mayr, 1861: 56 (w.q.); Perkins, 1891: 123 (gynandromorph). See also: Donisthorpe, 1915d: 139; Arnol'di, 1928b: 206; DuBois, 1993: 307; DuBois, 1998b: 226; Rigato, 2011: 14.

Type Material

Rigato (2011) - Lectotype male, UNITED KINGDOM (Oxford University Museum of Natural History) [not examined]. Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Rigato (2011) - TL 3.7–4.3; HL 0.83–0.92; HW 0.68–0.78; CI 82–86; SL 0.63–0.70; SI 89–93; PCI 18–23; PnW 0.46–0.52; AL 1.05–1.15; PSI 1.22–1.52; PeL 0.37–0.43; PPL 0.25–0.28; PeH 0.21–0.25; PPH 0.22–0.25; PeW 0.16–0.20; PPW 0.23–0.26; PI1 65–68; PI2 54–55; MTL 0.59–0.67; TI 83–87 (4 measured).

Queen

Rigato (2011) - TL 4.5–4.7; HL 0.91–0.95; HW 0.75–0.79; CI 82–84; SL 0.70–0.72; SI 91–93; PCI 22–23; AL 1.32–1.35; PSI 1.61–1.84; ScW 0.63–0.67; MnL 0.94–0.99; PeL 0.46–0.49; PPL 0.28–0.31; PeH 0.25–0.26; PPH 0.26–0.29; PeW 0.20–0.21; PPW 0.27–0.31; PI1 61–64; PI2 60–62; MTL 0.67–0.72; TI 85–96 (3 measured).

Male

Rigato (2011) - TL 3.8–4.0; HL 0.64–0.73; HW 0.58–0.62; CI 85–91; SL 0.22–0.25; SI 38–40; AL 1.27–1.35; ScW 0.59–0.65; MnL 0.88–0.97; PeL 0.39–0.45; PPL 0.24–0.28; PeH 0.21; PPH 0.22; PeW 0.19; PPW 0.26–0.27; PI1 62; PI2 67–73; MTL 0.88–0.91; TI 147–152 (2 measured).

Karyotype

  • n = 20 (Crozier, 1975).

References