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Figs. 34, 81- 82.
Monomorium (Syllophopsis) modestum var. boerorum Santschi HNS 1915:260, fig. 9 ([[worker]]). [Junior primary homonym of Monomorium minutum var. boerorum Forel HNS , 1910b:442.]. Syntype [[worker]], South Africa: Transvaal, Pretoria (NHMB) [examined].
Material examined.- M. modestum transwaalense HNS (corrected ending): Syntype: [[worker]], South Africa (Transvaal), Pretoria (NHMB - Reg. No. 207). The syntype examined is headless. Other, more complete syntypes may be in existence, hence this specimen has not been designated a lectotype.
Other material examined: Prov. Antananarivo: 3 km 41 NE Andranomay, 11.5 km 147 SSE Anjozorobe 5-13.xii.2000 Fisher et al. (225). Prov. Fianarantsoa: 45 km S Ambalavao 25.ix.1992 B.L. Fisher (4 5); 43 km S Ambalavao Res., Andringitra 5.x.1993 B.L. Fisher (3 [[worker]]); P.N. Ranomafana, Vatoharanana 4.1 km 231 SW Ranomafana 27-31.iii.2003 Fisher et al. (4 5). Prov. Toamasina: 6.9 km NE Ambanizana, 2.xii.1993 BL. Fisher (45); F C. Sandranantitra 18-21.i.1999 (145) 21-24.x.1999 (3 [[worker]]) H.J. Ratsirarson. Prov. Toliara: P.N. Andohahela, 3.8 km 113 ESE Mahamavo 21-25.i.2002 Fisher et al. (2 [[worker]]); P.N. Tsingy de Bemaraha, 3.4 km 93 E Bekopaka 6-10.xi.2001 Fisher et al. (1 [[worker]]).
Worker description.- Head: Head rectangular; vertex planar; frons shining and smooth except for piliferous pits; pilosity of frons a mixture of incurved, semi-erect setae and slightly shorter decumbent setae. Eye minute, eyes consisting of one or two ommatidia only; (in full-face view) eyes set at about midpoint of head capsule; (viewed in profile) eyes set around midline of head capsule, or, set posteriad of midline of head capsule; Antennal segments 12; antennal club three-segmented. Clypeal carinae weakly to strongly defined; anteromedian clypeal margin emarginate, clypeal carinae indistinct, or, emarginate, clypeal carinae terminating in blunt angles, or, emarginate, clypeal carinae terminating in small denticles; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin extending slightly beyond level of posterior margin of antennal fossae. Anterior tentorial pits situated nearer mandibular insertions than antennal fossae. Frontal lobes sinuate, divergent posteriad. Psammophore absent. Palp formula 2,2. Mandibular teeth four; mandibles linear-triangular and smooth (except for piliferous pits); masticatory margin of mandibles strongly oblique; basal tooth approximately same size as t3 (four teeth present).
Mesosoma: Promesonotum shining and mainly smooth, vestigial striolae, if present, confined to lower anterior mesopleuron; (viewed in profile) anterior promesonotum smoothly rounded, thereafter more-or-less flattened, promesonotum on same plane as propodeum; promesonotal setae greater than twelve; standing promesonotal setae consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae; appressed promesonotal setulae few, mainly on sides of promesonotum. Metanotal groove strongly impressed, with distinct transverse costulae, or vestigial. Propodeum shining and smooth, metapleuron with a few weak striolae; propodeal dorsum flat throughout most of its length; propodeum smoothly rounded or with indistinct angle; standing propodeal setae consisting of one prominent pair anteriad, with a few to many erect to decumbent setae on/around dorsal and declivitous faces of propodeum; appressed propodeal setulae very sparse or absent; 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 and situated within anterior sector of petiolar node; node (viewed in profile) conical, vertex rounded; appearance of node shining and smooth throughout; 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; ventral petiolar lobe present; height ratio of petiole to postpetiole between 3:2 and 4:3; height -length ratio of postpetiole about 1:1; postpetiole shining and smooth; postpetiolar sternite depressed at about its center, with anterior process developed as a short, conspicuous spur angled at 45-90.
Gaster: Pilosity of first gastral tergite consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae.
General characters: Color depigmented creamy yellow. Worker caste monomorphic.
Syntype worker measurements: Measurements not taken as syntype is headless.
Other worker measurements: HML 1.21-1.44 HL 0.46-0.52 HW 0.36-0.41 CeI 77-80 SL 0.33-0.39 SI 90-97 PW 0.22-0.30 (n=20).
Remarks.- At the time of writing, type material for Monomorium modestum HNS is missing (per Dr. D. Burckhardt, NHMB, pers. commun.), and the syntype of Monomorium modestum transwaalense HNS (i.e., previously M. modestum boerorum HNS ) available to me for examination is headless, hence the identification of the Malagasy material as Monomorium modestum HNS is provisional. Bolton (1987) uses the morphology of the propodeum and the nature of the metanotal groove to distinguish M. modestum HNS from other African ants in that species group. The transwaalense syntype, however, clearly has an angulate propodeum that approximates to what can be found in many Monomorium cryptobium HNS specimens. In workers of these small ants propodeal denticles are not always present. Moreover, the transwaalense syntype has quite a distinct metanotal impression, not the "simple indentation" that Bolton mentions. The Malagasy material, on the other hand, does have a much more rounded propodeum and the metanotal groove is indeed simply a weak impression. In fact, Malagasy workers have much more of the appearance of Fig. 95 in Bolton"s monograph than the transwaalense syntype. Electronic images of worker material collected many years ago in Natal and identified (probably by Arnold: H. Robertson pers. commun.) as M. modestum HNS have been sent to me by Dr. Hamish Robertson (South African Museum), and these appear to be identical with the Malagasy workers. This raises the possibility that Monomorium modestum HNS and Monomorium modestum transwaalense HNS may not be conspecific. The general appearance of the transwaalense syntype suggests M. sechellense HNS , but in that species the propodeum is distinctly dentate and the mesopleuron is sculptured, whereas this is not the case with transwaalense.
On Madagascar Monomorium modestum HNS has a known distribution that is exactly complementary to that of M. sechellense HNS , the latter occupying the drier west coast of Madagascar and the former the more humid east coast. Populations of these two species converge in the south near the Isantoria River (Toliara Province). The workers of M. modestum HNS are nearly identical in appearance to small, depigmented yellow workers of M. hildebrandti HNS , from which they differ only in the form of the compound eye. The weakly angulate to rounded propodeum enables Malagasy workers of the species to be separated from those of Monomorium cryptobium HNS and M. sechellense HNS . Queens and males are not represented in the CAS collection. With the exception of one worker taken in a pitfall trap, the universal collection method for this species has been sifted litter. All specimens have been collected in rainforest.