Monomorium hanneli

Monomorium hanneli has been collected throughout the island of Madagascar, most frequently near the coast. The usual habitat is rainforest, though it also occurs in dry tropical forest and spiny forest. Sifted leaf litter has been the usual collection method, but the nest series was taken from under a stone. (Heterick 2006)

Identification
Monomorium hanneli is distinctive throughout its range, being the only member of its species group in Madagascar. The main variation is a pale worker morphotype that has been found in most of the major collection localities, usually in the same transects, as the normal, darker morphotype. Since it has occasionally been collected in the same pitfall trap or in a pitfall trap adjacent to one in which the darker morphotype has been captured, it may conceivably occur within the same nests. This, however, cannot be established with certainty, as only one CAS nest series of just eight workers of this small species is known. The normal worker is usually yellow-orange to tawny orange, with a distinct metanotal groove and angulate propodeum. Well-spaced, erect setae are the usual pilosity pattern on the gaster and the antennal scape, the latter also possessing decumbent setae. The pale yellow or orange form has a much more rounded mesosoma profile, almost crescentic, with a less angulate propodeum. The head in profile is rather fuller than the normal morphotype, which, together with the rounded mesosoma, gives the ant somewhat of a bloated appearance. The gastral setae are abundant and decumbent, the setae on the scape decumbent or appressed. The appearance is reminiscent of a larger Monomorium chnodes. Whatever the reason for these differences, the pale workers are not simply tenerals, since their morphology differs from that of other workers. Queens of the pale morphotype also exist, and the same differences in pilosity noted below (see description) are the major distinction between these and the normal, darker form. The queen is a bright orange. The distinction between the two forms, however, is not clear-cut and individuals with an intermediate appearance occasionally occur.

The types described from African worker material differ from Malagasy material in being slightly (Monomorium hanneli, M. valtinum) to considerably (Monomorium moestum) darker with a more brownish or reddish tinge to the cuticle, and in having very small but sharp clypeal denticles. Malagasy populations of this ant range from yellow to tawny orange, and the anteromedian clypeal margin is either straight or weakly emarginate with blunt to sharp angles rather than denticles. I understand these to be non-significant differences, M. hanneli revealing considerable variation in color and morphology among both African and Malagasy populations.

Bolton (1987) separated two ostensibly different Kenyan forms, the smaller Monomorium valtinum and the larger M. hanneli, principally on the basis of the smaller eye in M. valtinum. This researcher had relatively few specimens available to him and these excluded queens and males. In Madagascar, by contrast, what I take to be M. hanneli is very common and I have been able to examine hundreds of specimens, including over twenty queens and around a dozen males (my descriptions being based on 20 of the former and 11 of the latter). The size of the eye is clearly variable: the number of ommatidia in workers examined ranges from six, in paired rows of three, to at least sixteen with three transverse rows of four ommatidia. On one pin holding three workers of a nest series, the middle worker had 16 ommatidia visible under a stereomicroscope, the other two 11. The body size of Malagasy workers also overlaps the parameters of the morphometric measurements given by Bolton for the two taxa. For this reason, I consider M. valtinum and M. hanneli to be representatives of the same species, and M. valtinum becomes a junior synonym in this work. The queens and males generally have lightly-sclerotized wing veins, with vein M indistinct distally in the male. Vein m–cu has been absent from the wings of all males examined thus far, but is occasionally present in alate queens.

Distribution based on Regional Taxon Lists
Afrotropical Region: Comoros, Kenya, United Republic of Tanzania, Mozambique.

Nomenclature

 *  hanneli. Monomorium hanneli Forel, 1907a: 18 (w.) KENYA. Heterick, 2006: 155 (q.m.). Senior synonym of moestum: Bolton, 1987: 426; of valtinum: Heterick, 2006: 153.
 * moestum. Monomorium moestum Santschi, 1914b: 74, fig. 7 (w.) KENYA. Combination in M. (Notomyrmex): Emery, 1922e: 170. Junior synonym of hanneli: Bolton, 1987: 426.
 * valtinum. Monomorium valtinum Bolton, 1987: 428 (w.) KENYA. Junior synonym of hanneli: Heterick, 2006: 140.

Worker
Heterick (2006) - Holotype (M. hanneli): HML 1.43 HL 0.51 HW 0.43 CeI 84 SL 0.35 SI 81 PW 0.31. Lectotype (Monomorium moestum): HML 1.60 HL 0.56 HW 0.49 CeI 88 SL 0.38 SI 78 PW 0.34. (non-types): HML 1.22–1.49 HL 0.45–0.54 HW 0.38–0.45 CeI 82–87 SL 0.31–0.38 SI 82–86 PW 0.28–0.33 (n=20).

HEAD: Head rectangular; vertex planar or weakly concave; frons shining and smooth except for piliferous pits; pilosity of frons a mixture of incurved, semi-erect setae and slightly shorter decumbent setae. Eye small, eye width less than 1× greatest width of antennal scape; (in full-face view) eyes set above midpoint of head capsule; (viewed in profile) eyes set posteriad of 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 weakly to strongly defined; anteromedian clypeal margin emarginate, clypeal carinae terminating in blunt angles; 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 antennal fossae than mandibular insertions; 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 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 few, mainly on sides of promesonotum. Metanotal groove strongly impressed, with distinct transverse costulae. Propodeum shining, dorsum and sides of propodeum mainly smooth, with weak to strong striolae on declivitous face and on metapleuron; propodeal dorsum slightly elevated anteriad and sloping away posteriad, propodeal angles not raised; propodeum distinctly angulate, propodeal angle sharp; length ratio of propodeal dorsum to its declivity about 3:2; 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 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 4:3 and1:1; anteroventral petiolar process present as a thin flange tapering posteriad; ventral petiolar lobe present; height ratio of petiole to postpetiole between 4:3 and 1:1; height–length ratio of postpetiole between 3:4 and 1:2; postpetiole shining and smooth; postpetiolar sternite depressed at about its center, with anterior process developed as a short, conspicuous spur angled at 45–90, or, not depressed at midpoint, its anterior end an inconspicuous lip or small carina.

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

GENERAL CHARACTERS: Color yellowish to tawny orange. Worker caste monomorphic.

Queen
Heterick (2006) - HML 1.40–1.71 HL 0.47–0.57 HW 0.41–0.48 CeI 84–89 SL 0.34–0.41 SI 80–85 PW 0.31–0.44 (n=20).

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: Mesoscutum broadly convex anteriad, convexity reduced posteriad; 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 3:2 and 4:3; axillae contiguous, or nearly so; standing pronotal/mesoscutal setae consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae; appressed pronotal, mescoscutal and mesopleural setulae few, mainly on sides of pronotum and mesopleuron. Propodeum shining and smooth, metapleuron with a few distinct striolae; propodeum angulate, propodeal angle blunt, or, distinctly angulate, propodeal angle sharp; propodeal dorsum flat throughout most of its length, or, sloping posteriad, and depressed between raised propodeal angles; standing propodeal setae consisting of one pair of prominent setae anteriad, with a few smaller, erect to decumbent setae on and around dorsal and declivitous faces; appressed propodeal setulae very sparse or absent; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum; propodeal lobes present as well-developed, rounded flanges.

WING: Wing veins tubular and strongly sclerotised; vein m–cu present in some individuals; vein cu–a present.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated slightly anteriad of petiolar node, or, lateroventral and situated within anterior sector of petiolar node; node (viewed in profile) cuneate, vertex tapered; appearance of node shining and smooth; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 3:2 and 1:1; anteroventral petiolar process absent or vestigial; height ratio of petiole to postpetiole about 4:3; height–length ratio of postpetiole between 3:2 and 4:3; postpetiole shining and smooth; postpetiolar sternites depressed at about its center, with anterior process developed as a short, conspicuous spur angled at 45–90º, or, not depressed, its anterior end an inconspicuous lip or small carina.

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 yellow-orange, gaster may have brownish tint. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.

Male
Heterick (2006) - HML 1.34–1.61 HL 0.44–0.48 HW 0.39–0.44 CeI 88–98 SL 0.11–0.13 SI 28–31 PW 0.44–0.52 (n=11).

HEAD: (In full-face view) head width–mesosoma width ratio between 1:1 and 3:4; frons finely micropunctate. Compound eyes protuberant and elliptical; margin of compound eye clearly separated from posterior margin of clypeus. Ocelli not turreted. Ratio of length of first funicular segment of antenna to second funicular segment between 2:3 and 1:2. Maximum number of mandibular teeth and denticles two.

MESOSOMA: Mesoscutum broadly convex; a few vestigial striolae on dorsum of mesoscutum, otherwise smooth and shining; parapsidal furrows vestigial or absent; notauli absent; axillae separated by width of at least one axilla.

WING: Wing veins with vein M indistinct distally, otherwise tubular and sclerotised; vein m–cu absent; vein cu–a present.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node (viewed in profile) cuneate, vertex tapered, or, conical, vertex tapered; appearance of node shining and smooth; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 3:2 and 4:3, or, 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 about 3:2; postpetiole shining and smooth.

GASTER: Pilosity of first gastral tergite consisting of well-spaced, semi-erect setae.

GENERAL CHARACTERS: Color brown, head darker, appendages light brown.

Type Material
Heterick (2006) - Holotype: worker, Kenya, Mto-ya-Kifaru (Katona). This worker was designated a ‘holotype’ by Bolton (1987), and since the length is given as a single measurement, it seems clear no other specimens were examined. Holotype status based on monotypy (Code 73.1.2) is here assumed.