Monomorium lepidum

As with many of small Malagasy Monomorium, the species has a predilection for rotten twigs and tree stumps, but also features prominently in sifted litter and pitfall-trapped samples.

Identification
Heterick (2006) - A member of the M. flavimembra complex in the M. monomorium species group. This handsome, bicolored species can easily be mistaken for the ‘binatu’ form of Monomorium termitobium, but lacks the sharply defined, narrowly separated clypeal carinae and strongly projecting clypeus of the latter. The proper affinities of this ant lie with Monomorium flavimembra and its allies. Workers within a series are of uniform appearance, either bright yellow or orange with a dark brown gaster. The gaster is typically uniformly dark, but the base of the first gastral tergite may be a cloudy brownish-yellow. Sometimes the postpetiole is also dark brown. As with M. flavimembra, the basal mandibular tooth is greatly reduced, but is at least represented by a faint angle in all specimens seen.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Habitat
Tropical dry forest is a typical habitat, but several series have come from rainforest.

Nomenclature

 *  lepidum. Monomorium lepidum Heterick, 2006: 126, figs. 20, 57, 58 (w.q.) MADAGASCAR.

Worker
Holotype: HML 1.25 HL 0.48 HW 0.40 CeI 84 SL 0.36 SI 90 PW 0.25.

HML 1.09–1.38 HL 0.44–0.54 HW 0.37–0.47 CeI 82–88 SL 0.34–0.42 SI 89–96 PW 0.22–0.29 (n=20).

HEAD: Head rectangular; vertex planar or weakly concave; frons shining and smooth except for piliferous pits; pilosity of frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter decumbent setae or setulae. Eye moderate, eye width 1–1.5× greatest width of antennal scape; (in full-face view) eyes set below midpoint of head capsule; (viewed in profile) eyes set around midline of head capsule; eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin. Antennal segments 12; antennal club three-segmented. Clypeal carinae partially developed or indistinct; anteromedian clypeal margin straight; 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 three, plus minute, basal denticle or angle; mandibles with sub-parallel inner and outer margins, smooth (except for piliferous pits); masticatory margin of mandibles approximately vertical or weakly oblique; basal tooth a small to minute denticle or angle, much smaller than t3 (four teeth present).

MESOSOMA: Promesonotum shining and mainly smooth, vestigial striolae, if present, confined to lower anterior mesopleuron; (viewed in profile) promesonotum broadly convex anteriad, convexity reduced posteriad; promesonotal setae seven to twelve; standing promesonotal setae a mixture of well-spaced, distinctly longer, erect and semi-erect setae which are curved distally and often paired, interspersed with much shorter, incurved, decumbent setae; appressed promesonotal setulae very sparse or absent. Metanotal groove strongly impressed, with distinct transverse costulae. Propodeum shining and smooth, with a few weak striolae on metapleuron; propodeal dorsum convex; propodeum always smoothly rounded; standing propodeal setae consisting of one prominent pair anteriad, with other shorter setae very sparse or absent; appressed propodeal setulae very sparse or absent; propodeal spiracle nearer metanotal groove than declivitous face of propodeum, or, equidistant from metanotal groove and declivitous face of propodeum. Vestibule of propodeal spiracle distinct in some specimens. Propodeal lobes present as rounded flanges.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node (viewed in profile) cuneate, vertex tapered; appearance of node shining and smooth throughout; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 1:1 and 3:4; anteroventral petiolar process absent or vestigial; ventral petiolar lobe present; height ratio of petiole to postpetiole about 4:3; height–length ratio of postpetiole between 4:3 and 1:1; postpetiole shining and smooth; postpetiolar sternite without anterior lip or carina, or this structure vestigial.

GASTER: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.

GENERAL CHARACTERS: Color of foreparts tawny-yellow to orange (postpetiole sometimes darker), gaster chocolate. Worker caste monomorphic.

Queen
HML 1.99–2.34 HL 0.56–0.59 HW 0.55–0.58 CeI 96–105 SL 0.47–0.49 SI 82–86 PW 0.40–50 (n=3).

HEAD: Head rectangular; vertex weakly concave or planar; frons shining and smooth except for piliferous pits and a few striolae around antennal sockets and frontal carinae; pilosity of frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter setae or setulae, which are decumbent or appressed, longer setae thickest on vertex. Eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin; (in full-face view) eyes set at about midpoint of head capsule; (viewed in profile) eyes set posteriad of midline of head capsule.

MESOSOMA: Anterior mesoscutum smoothly rounded, thereafter more-or-less flattened; pronotum, mesoscutum and mesopleuron shining and mainly smooth, vestigial striolae, if present, confined to anterior katepisternum; 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 a mixture of well-spaced, distinctly longer, erect and semi-erect setae which are curved distally, interspersed with much shorter, incurved, decumbent setae; appressed pronotal, mescoscutal and mesopleural setulae few, mainly on sides of pronotum and mesopleuron; propodeum shining and smooth, with multiple hair like striolae on metapleuron. Propodeum always smoothly rounded; propodeal dorsum convex; standing propodeal setae consisting of up to a dozen or more longer erect and shorter sub-erect setae; appressed propodeal setulae very sparse or absent; propodeal spiracle nearer metanotal groove than declivitous face of propodeum; propodeal lobes present as well-developed, rounded flanges; Petiolar spiracle lateral and situated within anterior sector of petiolar node.

WING: Wing not seen (queens dealated).

PETIOLE AND POSTPETIOLE: node (viewed in profile) conical, vertex rounded; appearance of node shining and weakly striolate posteriad; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 4:3 and 1:1; anteroventral petiolar process absent or vestigial; height ratio of petiole to postpetiole between 4:3 and 1:1; height–length ratio of postpetiole between 4:3 and 1:1; postpetiole shining and weakly striolate posteriad; postpetiolar sternites without anterior lip or carina, or this structure vestigial.

GASTER: Pilosity of first gastral tergite consisting of a mixture of incurved, erect and semi-erect setae and slightly shorter decumbent setae.

GENERAL CHARACTERS: Color of foreparts yellow-orange, gaster chocolate. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.

Type Material
Holotype: worker, Prov. Mahajanga, Forêt de Tsimembo, 11.0 km 346 NNW Soatana, 50 m 19°00′S, 44°27′E, 21–25.xi.2001, Fisher et al. BLF/ex dead twig above ground tropical dry forest/ CASENT 0442208 4561. Paratype: Prov. Mahajanga (all specimens with same collection data as holotype): 1 worker ; 1 queen + 13 workers ; 1 worker (CAS); 23 workers.

Etymology
Latin ‘lepidus’ (‘elegant’)

References based on Global Ant Biodiversity Informatics

 * Goodman S., Y. Anbdou, Y. Andriamiarantsoa, B. L. Fisher, O. Griffiths, B. Keitt, J. J. Rafanomezantsoa, E. Rajoelison, J. C. Rakotonirina, L. Ranaivoarisoa et al. 2017. Results of a biological inventory of the Nosy Ankao island group, Parc National de Loky-Manambato, northeastern Madagascar. Malagasy Nature, Association Vahatra, 2017, 11, 
 * Heterick B. 2006. A Revision of the Malagasy Ants Belonging to Genus Monomorium Mayr, 1855 (Hymenoptera: Formicidae). Proceeding of the California Academy of Sciences (PCAS) 57: 69-202
 * Ravelomanana A., and B. L. Fisher. 2013. Diversity of ants in burned and unburned grassland, and dry deciduous forest in the Beanka Reserve, Melaky Region, western Madagascar. Malagasy Nature 7: 171-183.