Monomorium bicolor

Identification
Bolton (1987):

Worker. TL 3.2-3.9, HL 0.70-0.93, HW 0.52-0.75, CI 73-83, SL 0.56-0.78, SI 104-115, PW 0.36-0.50, AL 0.82-1.20 (25 measured).

Third and fourth (basal) tooth of mandible approximately the same size or the fourth very slightly smaller than the third, but the basal tooth never reduced to a minute denticle. Median portion of clypeus with its anterior free margin usually indented, more rarely the margin approximately transverse but never with flanking sharp teeth. Eyes of moderate size, the maximum diameter 0.24-0.27 x HW. Ventral surface of head with curved simple hairs but lacking extremely long J-shaped ammochaete hairs. Dorsal alitrunk hairless, petiole with one pair and postpetiole with 1-2 pairs of posteriorly directed hairs. Discounting the apical transverse row the first gastral tergite usually with only 1-2 pairs of hairs, situated on the basal half; rarely 3-4 pairs of hairs present. Dorsum and sides of head and entirety of alitrunk densely and sharply reticulate-punctate. Gaster usually finely and densely shagreenate dorsally but the sculpture may fade posteriorly in some examples and is reduced in a few. Colour bright orange to red on the head and alitrunk, the gaster blackish brown to black, the two strongly contrasting. First gastral tergite frequently with an anteromedian paler area.

In the bicolor-complex Monomorium bicolor differs from its closest relatives in that it lacks the densely hairy alitrunk seen in Monomorium hirsutum, has such smaller eyes than Monomorium personatum (0.31-0.33 x HW), lacks the reduced basal mandibular tooth of Monomorium rufulum, lacks the pair of sharp clypeal teeth characteristic of Monomorium westi, and lacks the dense gastral pilosity of Monomorium dictator.

Distribution based on Regional Taxon Lists
Afrotropical Region: Burkina Faso, Cameroun, Democratic Republic of Congo, Djibouti, Eritrea, Ethiopia, Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Kenya, Liberia, Nigeria, Saudi Arabia, Senegal, Sudan, Togo, United Arab Emirates. Neotropical Region: Dominican Republic, Greater Antilles. Palaearctic Region: Egypt.

Biology
Bolton (1987) - In sub-Saharan Africa Monomorium bicolor is characteristically a species of open savannah or semi-arid zones, but it also occurs in forested areas where there is some direct insolation, often being found on forest paths in Nigeria and Ghana. Nests are constructed directly into the earth and the species appears to be a general scavenger in habits, quickly appearing in traps baited with crushed large insects.

Nomenclature

 *  bicolor. Monomorium bicolor Emery, 1877b: 368 (w.) ETHIOPIA. Mayr, 1901b: 7 (q.). Combination in M. (Xeromyrmex): Wheeler, W.M. 1922a: 868. Subspecies of subopacum: Santschi, 1927d: 244; Santschi, 1935b: 268. Revived status as species: Santschi, 1937d: 222; Bolton, 1987: 338. Senior synonym of coerulescens: Santschi, 1914d: 353 (in key); Bolton, 1987: 338; of aequatoriale, rufibasis, uelense, tropicale: Bolton, 1987: 338. Current subspecies: nominal plus judaicum.
 * coerulescens. Monomorium bicolor var. coerulescens Santschi, 1912c: 148 (w.) DJIBOUTI. Junior synonym of bicolor: Santschi, 1914d: 353 (in key); Bolton, 1987: 338.
 * rufibasis. Monomorium bicolor var. rufibasis Santschi, 1914d: 353 (diagnosis in key) (w.) EGYPT. Santschi, 1927d: 244 (q.m.). [Misspelled as rufobasalis by Santschi, 1926b: 240.] Junior synonym of bicolor: Bolton, 1987: 338.
 * aequatoriale. Monomorium (Xeromyrmex) bicolor var. aequatoriale Santschi, 1926b: 240 (w.) CAMEROUN. Junior synonym of bicolor: Bolton, 1987: 338.
 * tropicale. Monomorium (Xeromyrmex) bicolor var. tropicale Santschi, 1926b: 240 (w.q.m.) DEMOCRATIC REPUBLIC OF CONGO. Junior synonym of bicolor: Bolton, 1987: 338.
 * uelense. Monomorium (Xeromyrmex) bicolor var. uelense Santschi, 1926b: 239 (w.) DEMOCRATIC REPUBLIC OF CONGO. [Misspelled as uluense by Santschi, 1926b: 240.] Junior synonym of bicolor: Bolton, 1987: 338.

Worker
Bolton (1987) - TL 3.2-3.9, HL 0.70-0.93, HW 0.52-0.75, CI 73-83, SL 0.56-0.78, SI 104-115, PW 0.36-0.50, AL 0.82-1.20 (25 measured).

Third and fourth (basal) tooth of mandible approximately the same size or the fourth very slightly smaller than the third, but the basal tooth never reduced to a minute denticle. Median portion of clypeus with its anterior free margin usually indented, more rarely the margin approximately transverse but never withftanking sharpteeth. Eyes of moderate size, the maximum diameter 0.24-0.27 x HW. Ventral surface of head with curved simple hairs but lacking extremely long J-shaped ammochaete hairs. Dorsal alitrunk hairless, petiole with one pair and postpetiole with 1-2 pairs of posteriorly directed hairs. Discounting the apical transverse row the first gastral tergite usually with only 1-2 pairs of hairs, situated on the basal half; rarely 3-4 pairs of hairs present. Dorsum and sides of head and entirety of alitrunk densely and sharply reticulate-punctate. Gaster usually finely and densely shagreenate dorsally but the sculpture may fade posteriorly in some examples and is reduced in a few. Colour bright orange to red on the head and alitrunk, the gaster blackish brown to black, the two strongly contrasting. First gastral tergite frequently with an anteromedian paler area.

Type Material
Syntype workers, ETHIOPIA: Sciotel, Bogos, 1870 (O. Beccari) [examined].

Monomorium bicolor var. coerulescens Santschi, 1912: 148. Holotype worker, DJIBOUTI: Obock, 1893 (M. Maindron) [examined].

Monomorium bicolor var. rufibasis Santschi, 1914c: 353. Syntype workers, EGYPT: Upper Egypt (diagnosis in key) (not in, presumed lost).

Monomorium (Xeromyrmex) bicolor var. uelense Santschi, 1926a: 239. Syntype workers, ZAIRE: Haut Uele, Moto, 1920 (L. Burgeon) (NHMB; MRAC) [examined].

Monomorium (Xeromyrmex) bicolor var. aequatoriale Santschi, 19200: 240. Syntype workers, CAMEROUN: Gr. Batanga, 1911 (Schwab), (Wasmann) (NHMB) [examined].

Monomorium (Xeromyrmex) bicolorvar. tropicale Santschi, 19200: 240. Syntype workers, female, ZAIRE: Stanleyville (Majella) (NHMB) [examined].