Key to Afrotropical Messor species

Key to Messor workers, based on: Bolton, B. 1982. "Afrotropical species of the myrmicine ant genera Cardiocondyla, Leptothorax, Melissotarsus, Messor and Cataulacus (Formicidae)." Bulletin of the British Museum (Natural History) Entomology. 45:307-370.

This key is dated but can be useful for identifying many Messor specimens collected in the Afrotropical region. The following remarks from the paper that contains the key can also be helpful:

Among strongly polymorphic species such as these, where there is an enormous worker size-range, the standard measurements which I have otherwise used consistently for the Myrmicinae become meaningless and cannot be utilized. A few standard ratios have, however, proved to be of value in some cases and these are included in the relevant descriptions. The keys and descriptions are based on medium to large workers as these show the best discriminating characters, the minor workers of closely related species being sometimes indistinguishable. Size ranges covered by the descriptions are given for each species in terms of HW range.

The presence or absence of propodeal teeth or spines, which appears to be a functional diagnostic character in other parts of the range of Messor, is not of much use in the Ethiopian region species for, although some always have the propodeum armed (regularis, collingwoodi) and some always have it unarmed and rounded (angularis, luebberti), the rest show a disconcerting variability in this character, sometimes differing even in individuals from the same nest sample.

The 12 recognizable species are distributed roughly as follows in the Afrotropical region.

Northern (Sahelian) species: collingwoodi, galla, cephalotes (in extreme east).

Western species: regalis, galla (coastally).

Eastern species: cephalotes, angularis, luebberti (in south), galla (in north).

Southern species: denticornis, luebberti, striatifrons, tropicorum, piceus, decipiens, capensis.

The species fall into two groups in terms of pilosity. The first group, characterized generally by reduced pilosity and virtual absence of hairs on the first gastral tergite, contains the species angularis, collingwoodi, galla, and luebberti. In the second group pilosity is generally dense and is evenly distributed over the first gastral tergite. Included here are the remaining eight species noted above. Of them regalis is very conspicuous and not obviously close to any of the others. Of the remainder the southern complex of piceus, decipiens and capensis may represent a single species, and denticornis, striatifrons and tropicorum are closely related.

1

 * Hairs absent from first gastral tergite or at most with a single sparse transverse row at the extreme apex of the sclerite . . . . . 2


 * Hairs present on first gastral tergite, more or less evenly distributed over "the whole surface of the sclerite . . . . . 5

2
return to couplet #1
 * Dorsum of propodeum with one or more pairs of standing hairs . . . . . 3


 * Dorsum of propodeum without standing hairs . . . . . 4

3
return to couplet #2
 * Dorsum of head coarsely and densely reticulate-punctate everywhere, the mid-dorsal strip also rugulose. (Niger, Mali) . . . . . Messor collingwoodi


 * Dorsum of head smooth everywhere except for the rugulose mid-dorsal strip; without coarse dense reticulate-punctate sculpture. (Throughout Sahelian zone and northern East Africa, also occurring coastally in West Africa) . . . . . Messor galla

4
return to couplet #2
 * Head sculptured everywhere with close-packed longitudinal rugulae between which is reticulate-punctate ground-sculpture. Eyes slightly smaller, 0.15-0.18 x HW in HW range of 2.00-3.12. (Tanzania, Zimbabwe, Angola, Botswana, South West Africa, South Africa) . . . . . Messor luebberti


 * Head smooth except usually for a short central rugular area behind the frontal lobes. Eyes slightly larger, 0.18-0.21 x HW, in HW range of 2.00-2.76. (Kenya) . . . . . Messor angularis

5
return to couplet #1
 * Basal third or more of first gastral tergite strongly and conspicuously sculptured with rugulae, costulae, coarse reticulate-puncturation, or a combination of these . . . . . 6


 * Basal third of first gastral tergite unsculptured except for hair pits and very faint superficial patterning. In some very large workers a few short basigastral costulae may develop but these are restricted to the area immediately behind the postpetiole . . . . . 7

6
return to couplet #5
 * With the head in full-face view the sides with projecting hairs. Petiole and postpetiole coarsely closely and deeply rugose. (Nigeria, Benin Republic, Congo) . . . . . Messor regalis


 * With the head in full-face view the sides without projecting hairs. Petiole and postpetiole finely sculptured with feeble rugulae, dense puncturation or a combination of both. (Ethiopia, Kenya, Tanzania) . . . . . Messor cephalotes

7
return to couplet #5
 * Posterior half of clypeus between frontal lobes with a distinct, strongly raised central step or welt. (Angola, South West Africa) . . . . . Messor tropicorum


 * Posterior half of clypeus between frontal lobes without a raised central step or welt, usually more or less fiat or even slightly concave . . . . . 8

8
return to couplet #7
 * Eyes relatively large, the maximum eye diameter 0.21-0.25 x HW, in HW range of 2.50- > 4.00. (Botswana, South West Africa, South Africa) . . . . . Messor denticornis


 * Eyes smaller, the maximum eye diameter 0.14-0.19 x HW, in HW range of 2.50- > 4.00 . . . . . 9

9
return to couplet #8
 * In HW range 2.80- > 4.00 the sides of the head conspicuously evenly convex in full-face view. Propodeum in profile relatively long and low. (South West Africa, South Africa) . . . . . Messor striatifrons


 * In HW range 2.80- > 4.00 the sides of the head approximately straight' in full-face view, the sides parallel or divergent anteriorly. Propodeum in profile relatively short and high . . . . . 10

10
return to couplet #9
 * Body pilosity very dark in colour, deep red-brown to blackish. (Botswana, South Africa) . . . . . Messor piceus


 * Body pilosity pale, white or silvery to yellowish. . . . . . 11

11
return to couplet #10
 * Head red in major workers, contrasting in colour with the much darker alitrunk and gaster. (Zimbabwe, Botswana, Lesotho, South Africa) . . . . . Messor decipiens


 * Head brown to black in major worker, about the same colour as the alitrunk and gaster. (South West Africa, Botswana, South Africa) . . . . . Messor capensis