Monomorium egens

Usually egens nest in rotten wood in the soil or in fallen trunks, and forages in the wood and the surrounding leaf litter. More rarely the ants nest in rotten parts of standing trees, some distance above the ground. (Bolton 1987)

Identification
Bolton (1987) – This species, as presently constituted, is widely distributed in West and Central Africa and is quickly diagnosed by the construction of the pronotum, minute spiracle, small eyes and densely hairy scapes. This combination of characters, together with the others given above, lead me to treat all the samples listed below as members of a single species, but I am not truly convinced that this is correct. In some short series from Cameroun and Ghana the clypeus is much more shallowly concave than is usual and also in a Cameroun series the propodeum is more strongly convex in profile. A single worker, also from Cameroun, has the head and gaster much darker in colour than the alitrunk, with colours reminiscent of Monomorium floricola. Here again the anterior clypeal margin is almost transverse, much less concave than in egens holotype and most other samples, although the colours may indicate a teneral individual. Degree of convexity of the sides of the head varies from sample to sample and the petiole node in some is slightly inclined forward. Further study of egens, as it is presently understood, will be essential when more samples and especially longer series are available, and may lead to the recognition of two or even more species here.

Two closely related but distinctly different species occur in Cameroun, Monomorium draxocum and Monomorium noxitum. These have not been found anywhere else in West or Central Africa and both lack the characteristic pronotal structure of egens. A rather more distant relative is Monomorium strangulatum, known from Uganda and Tanzania, in which the number of antennal segments has been reduced from 12 to 11.

Distribution based on Regional Taxon Lists
Afrotropical Region: Angola, Cameroun, Democratic Republic of Congo, Ghana, Ivory Coast, Nigeria.

Nomenclature

 *  egens. Monomorium egens Forel, 1910e: 443 (w.) CAMEROUN. Senior synonym of jucundum, longiusculum: Bolton, 1987: 385.
 * jucundum. Monomorium jucundum Santschi, 1926b: 232 (w.) DEMOCRATIC REPUBLIC OF CONGO. Junior synonym of egens: Bolton, 1987: 385.
 * longiusculum. Monomorium longiusculum Santschi, 1926b: 237, fig. 3 (w.) DEMOCRATIC REPUBLIC OF CONGO. Junior synonym of egens: Bolton, 1987: 385.

Worker
Bolton (1987) – TL 2.0-2.5, HL 0.46-0.64, HW 0.39-0.54, CI 79-89, SL 0.33-0.47, SI 80-96, PW 0.24-0.30, AL 0.54-0.70 (28 measured).

Clypeal carinae moderately strongly developed, divergent anteriorly. Prominent median portion of clypeus relatively short, its anterior margin sometimes only shallowly concave but usually showing an extensive concavity. Angles where anterior and lateral margins of median section of clypeus meet lacking denticles or prominent angles. Maximum diameter of eye 0.19-0.21 x HW, the relatively small eyes with their posterior margins at or just in front of the midlength of the sides when seen in full-face view. Antennal scapes, when laid straight back from their insertions, failing to reach the occipital margin. In full-face view the sides of the head distinctly convex, the occipital margin broadly but shallowly concave. Pronotum almost or quite fiat transversely when viewed from behind and slightly above. The humeral corners in this view conspicuous and distinctly angular, rather than broadly evenly rounded, and the dorsum of the pronotum separated from the sides by bluntly angular longitudinal marginations. In profile the pronotum fiat to shallowly convex, sloping upwards posteriorly. The mesonotum convex and sloping posteriorly to the narrow but conspicuously impressed metanotal groove; the latter with short cross-ribs. Propodeal spiracle minute and pinhole-like, the dorsum of the segment shallowly convex in profile. Petiole node in profile bluntly subconical, with an inconspicuous narrow strip-like ventral process. Postpetiole smaller than petiole, lower and more broadly rounded. All dorsal surfaces of head and alitrunk with numerous standing hairs, the antennal scapes with long fine erect to suberect hairs. Head and body smooth and without sculpture except for minute hair-pits, metanotal cross-ribs and frequently (but not always) a narrow transverse reticulate band across the mesopleuron. Colour brown to blackish brown.

Type Material
Bolton (1987) – Holotype worker, Cameroun (Muralt) [examined].