Monomorium subopacum

Heterick (2006) - Monomorium subopacum, like Monomorium pharaonis, is something of a tramp, and its occurrence in Madagascar and other regions well away from its natural area of occurrence is certainly due to human activities (Bolton 1987).

Identification
Heterick (2006) - Monomorium subopacum is very similar to Monomorium willowmorense but those worker specimens I have seen of the former can be distinguished from M. willowmorense by their finely granulate-reticulate frons, uniformly sculptured promesonotal humeri and a longer antennal scape (SI > 100 in M. subopacum and < 100 in M. willowmorense). Nonetheless, the differences that separate the two are small, and in view of the variability to be found in M. subopacum I would not be surprised if molecular–based investigations resulted in M. willowmorense being added to the already overburdened synonymic list for M. subopacum.

Distribution based on Regional Taxon Lists
Afrotropical Region: Cape Verde, Niger, Senegal, United Arab Emirates. Malagasy Region: Madagascar. Oriental Region: India, Sri Lanka. Palaearctic Region: Algeria, Balearic Islands, Canary Islands, Georgia, Gibraltar, Greece, Iberian Peninsula, Italy, Lebanon, Malta, Oman, Portugal , Spain, Tunisia, Turkey.

Biology
Espadaler (2007) - On the Canary Islands this ant is found from sea level to a single outpost at 850 m, the Mirador de Isora, a highly degraded site.

Sharaf et al (2018) - Oman: collected in a dry valley planted with Acacia.

Nomenclature

 * glyciphila. Myrmica glyciphila Smith, F. 1858b: 125 (w.) SRI LANKA. Combination in Monomorium: Roger, 1863b: 32; in M. (Xeromyrmex): Emery, 1922e: 179. Junior synonym of subopacum: Bolton, 1987: 360.
 *  subopacum. Myrmica subopaca Smith, F. 1858b: 127 (w.q.) PORTUGAL (Madeira I.). Combination in Monomorium: Mayr, 1862: 753; in M. (Xeromyrmex): Wheeler, W.M. 1922a: 871. Subspecies of salomonis: Forel, 1890a: lxxv; Forel, 1907a: 18; Emery, 1908h: 676; Forel, 1910a: 23; Arnold, 1916: 224; Santschi, 1921e: 170; Santschi, 1923e: 281; Menozzi, 1926b: 182; Wheeler, W.M. 1927g: 107. Status as species: Emery, 1881b: 531; Emery, 1893c: 82; Mayr, 1895: 133; Bondroit, 1918: 143; Santschi, 1927d: 240; Santschi, 1931a: 4; Bolton, 1987: 360. Senior synonym of mediterraneum: Mayr, 1862: 753; Bolton, 1987: 360; of obscuripes: Santschi, 1927d: 241; of italica: Baroni Urbani, 1968b: 450; of cabrerae, glyciphila, liberta, surcoufi and material of the unavailable name senegalensis referred here: Bolton, 1987: 360; of intermedium Hohmann, La Roche, et al., 1993: 155; of adoneum, apuleii, ebraicum: Heterick, 2006: 103; of minitiribe: Sharaf, Collingwood, et al., 2015: 54. Current subspecies: nominal plus planidorsum.
 * mediterraneum. Monomorium mediterraneum Mayr, 1861: 72 (diagnosis in key) (w.q.) SPAIN. Santschi, 1936a: 40 (m.). Subspecies of subopacum: Santschi, 1936a: 40. Junior synonym of subopacum: Mayr, 1862: 753; Roger, 1862c: 294; Bolton, 1987: 360.
 * cabrerae. Paraphacota cabrerae Santschi, 1919g: 405, fig. 1 (m.) SPAIN (Canary Is). Santschi, 1927d: 242 (w.q.). Combination in Monomorium: Santschi, 1927d: 241. Subspecies of subopacum: Santschi, 1927d: 241. Junior synonym of subopacum: Bolton, 1987: 360.
 * surcoufi. Paraphacota surcoufi Santschi, 1919d: 90, fig. 1 (m.) ALGERIA. Santschi, 1927d: 243 (w.q.). Combination in Monomorium: Santschi, 1927d: 243. Subspecies of subopacum: Santschi, 1927d: 243. Junior synonym of subopacum: Bolton, 1987: 360.
 * obscuripes. Paraphacota cabrerae st. obscuripes Santschi, 1921b: 424 (m.) SPAIN (Canary Is). Santschi, 1927d: 241 (w.q.). Combination in Monomorium: Santschi, 1927d: 241. Subspecies of subopacum: Santschi, 1936a: 40. Junior synonym of subopacum: Santschi, 1927d: 241; Bolton, 1987: 360.
 * apuleii. Monomorium (Xeromyrmex) subopacum var. apuleii Santschi, 1927d: 243 (w.q.m.) TUNISIA. Junior synonym of subopacum: Heterick, 2006: 103.
 * intermedium. Monomorium (Xeromyrmex) subopacum var. intermedium Santschi, 1927d: 242 (w.) SPAIN (Canary Is). [First available use of Monomorium (Xeromyrmex) salomonis subsp. subopacum var. intermedium Wheeler, W.M. 1927g: 108; unavailable name.] Junior synonym of subopacum: Hohmann, La Roche, et al., 1993: 155.
 * liberta. Monomorium (Xeromyrmex) subopacum var. liberta Santschi, 1927d: 243 (w.) SENEGAL. [First available use of Monomorium (Xeromyrmex) salomonis st. subopacum var. liberta Santschi, 1921e: 170; unavailable name.] Junior synonym of subopacum: Bolton, 1987: 360.
 * ebraicum. Monomorium (Xeromyrmex) subopacum var. ebraicum Menozzi, 1933b: 62 (w.m.) ISRAEL. Junior synonym of subopacum: Heterick, 2006: 103.
 * adoneum. Monomorium (Xeromyrmex) subopacum var. adoneum Santschi, 1936a: 41, fig. 22 (w.) LEBANON (caption to fig. 22 is misspelled adonis). [Monomorium (Xeromyrmex) subopacum var. adoneum Santschi, 1934d: 277. Nomen nudum.] Junior synonym of subopacum: Heterick, 2006: 103.
 * pestiferum. Monomorium (Xeromyrmex) salomonis st. pestiferum Santschi, 1936a: 57, figs. 20, 28, 30 (w.q.m.) ALGERIA. Junior synonym of obscuriceps: Ettershank, 1966: 91.
 * italica. Monomorium (Xeromyrmex) subopacum subsp. italica Baroni Urbani, 1964c: 154, figs. 2, 3 (w.) ITALY. Junior synonym of subopacum: Baroni Urbani, 1968b: 450.
 * mintiribe. Monomorium mintiribe Collingwood & Agosti, 1996: 350, fig. 23 (w.q.m.) OMAN. Junior synonym of subopacum: Sharaf, Collingwood, et al., 2015: 54.

Type Material
Lectotype: worker, Madeira, T. V. Wollaston. In view of the subtle differences that separate genuine good species in the M. salomonis group, I am designating a lectotype to fix the name ‘subopacum’, the type worker material of which is a richer reddish brown than the type material for M. glyciphilum. The syntype material is on a single card rectangle. The lectotype worker is the third worker from the RHS, seen from the rear. Paralectotypes: Three workers and three queens, carded on the same rectangle as the holotype (BMNH). No attempt has been made to separate the ants

Taxonomic Notes
Heterick (2006) - Bolton (1987) recognized this species from Madagascar on the basis of a short series from Maevatanana (“Maevantanara”); however, there are no Malagasy specimens in the CAS, despite the huge amount of Monomorium material collected by Brian Fisher and his teams since the early 1990s. The Malagasy component in the description and measurements provided above includes details from six specimens held at UCDC and three specimens from the same series held at MCZ.

Several of the synonyms are those of taxa originally described from males. The spurious genus ‘Paraphacota’ incorporated three such taxa, and what appears to me to be two distinct species. The male of Monomorium surcoufi and that of M. cabrerai are obviously identical, and easily recognized by their long, bicolored legs and completely hyaline wings. On the other hand, the male of Monomorium cabrerai obscuripes has relatively shorter, uniformly dark legs and brown wing veins. I have not seen nest material of Monomorium subopacum that has included males, but Bolton (1987) was in no doubt that the descriptions of M. surcoufi and M. cabrerai were based on ordinary males of M. subopacum. He followed Santschi in also placing M. cabrerai obscuripes under M. subopacum but allowed that it could be the male of Monomorium medinae Emery, a Canary Islands endemic, a view first broached by Wheeler (1927). Hohmann et al. (1993) included the two cabrerai taxa under Monomorium medinae, but omitted Monomorium surcoufi. This seems to me an odd judgement, and, indeed, Bolton (1995) did not mention these authors at all in relation to ‘Paraphacota’, but continued to consign all three taxa to synonymy under Monomorium subopacum. (NB. Dr. Xavier Espadaler [pers. commun.] also places M. cabrerai under M. subopacum, leaving M. cabrerai obscuripes as an unresolved puzzle, but has indicated that none of the males originally placed under ‘Paraphacota’ belongs to Monomorium medinae.)

Worker
Heterick (2006) - Lectotype (M. subopacum): HML 1.81 HL 0.67 HW 0.54 CeI 81 SL 0.56 SI 104 PW 0.35. Lectotype (Monomorium glyciphilum): HML 2.03 HL 0.72 HW 0.60 CeI 83 SL 0.62 SI 104 PW 0.39. Lectotype (Monomorium mediterraneum): HML 1.92 HL 0.70 HW 0.55 CeI 79 SL 0.58 SI 105 PW 0.36. Lectotype (Monomorium subopacum intermedium): HML 1.93 HL 0.71 HW 0.58 CeI 82 SL 0.59 SI 102 PW 0.36. (non-types): HML 1.77–2.12 HL 0.64–0.73 HW 0.52–0.61 CeI 80–85 SL 0.54–0.64 SI 104–108 PW 0.34–0.42 (n=9).

HEAD: Head rectangular; vertex planar or weakly concave; frons shining and finely microreticulate; pilosity of frons consisting of abundant, incurved, appressed setulae only. Eye large, eye width 1.5× greater than greatest width of antennal scape; eyes (in full-face view) set at about midpoint of head capsule; (viewed in profile) eyes set around midline of head capsule; elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin. Antennal segments 12; club three-segmented. Clypeal carinae indicated by multiple weak ridges; anteromedian clypeal margin emarginate, clypeal carinae terminating in blunt angles; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin approximately level with antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes straight, parallel. Psammophore absent. Palp formula 2,2. Mandibular teeth four; mandibles with sub-parallel inner and outer margins, striate; masticatory margin of mandibles approximately vertical or weakly oblique; basal tooth approximately same size as t3 (four teeth present).

MESOSOMA: Promesonotum shining and microreticulate throughout; in profile broadly convex anteriad, convexity reduced posteriad; promesonotal setae absent; appressed promesonotal setulae well-spaced over entire promesonotum. Metanotal groove weakly to strongly impressed, with distinct transverse costulae. Propodeum shining and microreticulate; propodeal dorsum flat throughout most of its length; angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity between 2:1 and 4:3; standing propodeal setae absent; appressed propodeal setulae well-spaced and sparse; propodeal spiracle nearer metanotal groove than declivitous face of propodeum; vestibule of propodeal spiracle absent or not visible; propodeal lobes present as rounded flanges.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral or laterodorsal and situated within anterior sector of petiolar node. Node (viewed in profile) cuneate, vertex rounded, or, conical, vertex rounded; appearance of node shining and distinctly microreticulate; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 1:1 and 3:4. Anteroventral petiolar process present as a thin flange tapering posteriad; ventral petiolar lobe present, but weakly developed to vestigial. Height ratio of petiole to postpetiole between 3:2 and 4:3; height–length ratio of postpetiole between 1:1 and 3:4; postpetiole shining and microreticulate; postpetiolar sternites without anterior lip or carina, or this structure vestigial.

GASTER: Pilosity of first gastral tergite consisting mainly of short, appressed setulae, together with one to several pairs of erect and semi-erect setae.

GENERAL CHARACTERS: Color mesosoma, nodes and legs orange-yellow, head and antennae brown, gaster dark brown. Worker caste monomorphic.

Queen
Heterick (2006) - HML 3.13–3.43; HL 0.91–0.92; HW 0.79–0.86; CeI 89–93; SL 0.70–0.79; SI 89–92; PW 0.68–0.74 (n=4).

(based on three paralectotype queens of Monomorium subopacum and one queen of Monomorium mediterraneum).— HEAD: Head square; vertex always planar; frons shining and finely longitudinally striolate and microreticulate; pilosity of frons consisting of well-spaced appressed setulae only. Eye roundly elliptical; in full-face view, eyes set above midpoint to of head capsule; in profile, eyes set posteriad of midline of head capsule.

MESOSOMA: Anterior mesoscutum smoothly rounded, thereafter more-or-less flattened; prono tum, mesoscutum and mesopleuron uniformly finely punctate-microreticulate; length-width ratio of mesoscutum and scutellum combined between 2:1 and 3:2. Axillae narrowly separated (i.e., less than width of one axilla). Standing pronotal/mesoscutal setae sparse or absent; appressed pronotal, mescoscutal and mesopleural setulae well- spaced over entire pronotum/mesonotum. Propodeum entirely microreticulate-striolate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum slightly elevated anteriad and sloping away posteriad, propodeal angles not raised; standing propodeal setae absent; appressed propodeal setulae well-spaced and sparse; propodeal spiracle nearer metanotal groove than declivitous face of propodeum; propodeal lobes present as well-developed, rounded flanges or bluntly angled flanges.

WING: Wing not seen (queens dealated).

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node, in profile, cuneate, vertex rounded; appearance of node matt and microreticulate, rugose posteriad; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1. Anteroventral petiolar process present as a thin flange tapering posteriad; height ratio of petiole to postpetiole between 3:2 and 1:1; height–length ratio of postpetiole between 4:3 and 1:1; postpetiole shining and microreticulate; postpetiolar sternite without anterior lip or carina, or this structure vestigial.

GASTER: Pilosity of first gastral tergite consisting of long, appressed setae and one or two semierect setae, or, standing setae completely absent.

GENERAL CHARACTERS: Color tawny, variegated brown. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.

Male
Heterick (2006) - LECTOTYPE (Monomorium surcoufi): HL 0.88 HW 0.98 CeI 111. (NB. Lectotype lacks antennae, postpetiole and gaster). HOLOTYPE (Monomorium cabrerai): HML (Holotype lacks postpetiole and gaster) HL 0.89 HW 0.96 CeI 108 SL 0.29 SI 30 PW 1.00. LECTOTYPE (Monomorium cabrerai obscuripes): HML 3.17 HL 0.79 HW 0.86 CeI 109 SL 0.30 SI 35 PW 0.80.

I have only seen damaged male specimens (lectotypes for the taxa Monomorium surcoufi, Monomorium cabrerai and Monomorium cabrerai obscuripes). As there has been controversy over the assignment to M. subopacum of at least the males of Monomorium cabrerai obscuripes and the other males are tattered and lack body parts, no formal description of the abovementioned males is included here.