Monomorium rhopalocerum

One collection was made from a garden, and this is the only information known about the biology of this species.

Identification
Bolton (1987) - M. rhopalocerum is closely related to Monomorium exchao, Monomorium binatu and Monomorium symmotu; and more distantly to Monomorium tablense. Of these five binatu has relatively long scapes (SI 100-105) which reach back to the occipital margin. Both binatu and tablense contrast with the remainder as their petiole nodes are relatively high and narrow as opposed to the broader lower nodes seen in the other three. M. rhopalocerum is larger than exchao and symmotu, and has a relatively broader head, but relative size of eyes and length of scapes fall into the same range in all three, though the scapes of rhopalocerum average a fractionally lower SI.

rhopalocerum - HW 0.42-0.50, CI 79-83, SL 0.36-0.44, SI 83-90, Diameter of eye 0.18-0.21 x HW.

symmotu - HW 0.36-0.39, CI 74-76, SL 0.34-0.35, SI 89-94, Diameter of eye 0.20-0.23 x HW.

exchao - HW 0.37-0.38, CI 74-76, SL 0.34, SI 89-91, Diameter of eye 0.20-0.21 x HW.

Apart from the dimensions symmotu differs from rhopalocerum by having the propodeal outline more evenly convex and more strongly convex immediately behind the metanotal groove. In exchao the propodeum behind the groove is more strongly raised in profile and passes through a much narrower curve into its posterior slope towards the declivity.

Distribution based on Regional Taxon Lists
Afrotropical Region: South Africa.

Nomenclature

 * hottentota. Monomorium minutum subsp. hottentota Emery, 1895h: 26 (q.) SOUTH AFRICA. Junior synonym of rhopalocerum: Bolton, 1987: 407.
 *  rhopalocerum. Monomorium rhopalocerum Emery, 1895h: 25, pl. 2, fig 29 (w.) SOUTH AFRICA. Senior synonym of hottentota, leimbachi: Bolton, 1987: 407.
 * leimbachi. Monomorium leimbachi Forel, 1914d: 246 (w.) SOUTH AFRICA. Junior synonym of rhopalocerum: Bolton, 1987: 407.

Bolton (1987) - Monomorium hottentota is given as a provisional synonym. This is because the type-series of rhopalocerum is based on workers and that of hottentota on females. I have not seen any samples which contain both females and workers but the overall marked similarity between these two short series, and the fact that both show the same data, leads me to suspect that they originated in a single series that was somehow later split up.

Worker
Bolton (1987) - TL 2.0-2.2, HL 0.53-0.60, HW 0.42-0.50, CI 79-83, SL 0.36-0.44, SI 83-90, PW 0.26-0.30, AL 0.55-0.60 (15 measured).

Anterior margin of prominent median portion of clypeus transverse to shallowly concave, rounding into the lateral margin; the two margins not separated by acute angles or projecting triangular denticles. Clypeal carinae narrow but sharply developed, the space between them extremely shallowly transversely concave. Clypeal carinae relatively close together posteriorly and subparallel, feebly diverging anteriorly. Eyes relatively small, their maximum diameter 0.18-0.21 x HW and with 6-7 ommatidia in the longest row. In full-face view the eyes conspicuously in front of the midlength of the sides of the head. Antennal scapes, when laid straight back from their insertions, failing to reach the occipital margin. Sides of head behind eyes approximately parallel, only extremely weakly convex and feebly convergent posteriorly. Occipital margin broad and usually very weakly and shallowly concave, at least medially. Promesonotal dorsum evenly broadly and shallowly convex in profile, sloping posteriorly to the broadly impressed metanotal groove. Metanotal cross-ribs relatively long and strong, conspicuous. Propodeal dorsum sloping posteriorly, rounding broadly and evenly into the declivity. Propodeal spiracle small. Subpetiolar process a narrow inconspicuous rim. Node of petiole in profile low and broad, broadly rounded above. Postpetiole much smaller than petiole, lower and its dorsal and anterior surfaces forming a single convexity. All dorsal surfaces of head and body with standing hairs, the promesonotum with 4-5 pairs. Mesopleuron shagreenate to finely reticulate in larger workers, partly smooth in small individuals. Sculpture otherwise absent except for scattered hair-pits and the conspicuous metanotal cross-ribs. Colour dull yellow, the gaster sometimes with a brownish tint.

Type Material
Bolton (1987) - Syntype workers, South Africa: Cape Town (E. Simon) [examined].