Polymorphism

The specimens in the photomontages are from Bossou, south eastern Guinea, collector Tatyana Humle (Humle 13); or Cameroun - south-western tropical coastal forest area between Edéa and Campo (McKey Wolbachia project,  Cameroon 11).

The various morphs are shown in detail on the Dorylus (Anomma) burmeisteri morphs page.

Full new description - Cameroon 11, Humle 13 ( major shown top right)
Overall - shiny matt, posterior gaster shiny dark chestnut, head and gaster darker but unicoloured
Cameroon 11 - TL 10.1 HW 2.75 HL 2.6 HD 1.8 CI 106 SL 1.25 SI 48 AL 3.25 PW 1.0 PetL 0.75 GL 3.5 MFL 2.4
Humle 13 - TL 10.05 HW 3.0 HL 2.6 CI 115 HD 2.0 SL 1.6 SI 61 AL 3.25 PW 1.0 PetL 0.7 GL 3.5 MFL 2.4
Head - subrectangular, widest about mid-length but only slightly wider than anterior margin; sides convex, first one-sixth angled out from anterior margin, then near straight to mid-length before curved narrowing, occipital border no more than 60% maximum width; posterior border moderately shallow scallop; sculpturation of extremely fine spiculation, almost effaced on posterior half of face, which has minute sparse hair pits; median line visible only on anterior half of face and slightly impressed forward; clypeal margin sinuous medially extended, with long moderately fine median straight hair, others (worn away) laterally; mandible moderately long and fairly slender, subapical teeth reduced to denticle, basal tooth triangular, interior hairs (worn away); scape moderately thick, progressively so from base to apex, apex itself somewhat swollen with rounded corners; funiculus basal segment narrow, 2 slightly thicker, rest relatively stout, 3-9 near equisized, apical 10 no more than twice 9; coarse pilosity giving bristly appearance; in profile quite bulbous, with relatively short frontal area, posterior corners rounded; very minute sparse pilosity on occiput.
Alitrunk - shallowly domed, all edges rounded, smooth drop from one-third point of pronotum to almost back of propodeum; flat unbroken line with pronotum and propodeum (more of a mesonotum step in Humle 13); spiracle circular distinctly rearward facing; propodeum with short vertical declivity; metapleural gland upper flange only a little longer than lower; very fine spiculation, as lateral head; no hairs except micropilosity on shoulders.
Petiole - rel long, flattened dome with high point ca one-third from front, posterior face a smooth curve from dorsum; dorsal view parallel sided (posteroventral processes in Humle 13); spiracle moderate and about halfway in petiole height; subpetiolar process a low triangle, point at rear; sculpturation as alitrunk; hairs none on dorsum, lower single pair mod long hairs several dorsally on one of two Humle 13.
Gaster - 1 & 2 with sculpturation as but finer than alitrunk; waisted 1-2; hairs not many at all and those flat not erect.
Legs - coxae quite long and slender; femora relatively broad and flat, matte; tibiae relatively wide, pilosity fine; tarsi moderately thick, bristly, claws heavy.

Minima morph
Head densely spiculate, matt, colour uniformly dark brown; dorsum with minute very sparse decumbent pilosity; funiculus with dense bristly but very short pilosity; area between frontal carinae distinctly raised.

Nigeria specimens (Taylor, 1980b: 13). These seem to vary from those I have recognized as burmeisteri and, so, I have kept this section as a record. WORKERS. TL 10.88-3.86 mm. At least five morphs; largest HL 2.72, HW 2.66, SL 1.39, PW 1.27, petiole length 1.00
Colour dark red-brown. All over sculpturation of very fine reticulation. Several erect hairs on tergites, a pair on petiole dorsum and several subpetiole. Head with maximum width at mid-length then straight sided forward narrowing before the anterior margin. Antennal scapes thickening to a moderately broad apex; funiculus with all segments, except apical 10, near equisized and slightly longer than broad. Mandibles with a long acute apical tooth and a simple triangular preapical tooth subtended by a wrinkled inner margin running to a large blunt basal tooth. Anterior clypeal margin with a low, blunt medial extension; a long medial seta and a pair of moderately long hairs each side of it. Head highly polished but with with very sparse minute puncturations, and faint spiculation more dorsally and laterally. Promesonotum convex dorsally. Subpetiolar process broad-based but low, rear facing and blunt triangular.
Collected at the Cocoa Research Institute of Nigeria, Idi Ayunre.

Biology of "nigricans senso lato"

Often, cited (as nigricans) as being the subject of the classic early paper by the Rev. T.S. Savage, a medical missionary in West Africa, but that probably now can be separated as Dorylus rubellus.

Bernard (1952) wrote of "nigricans" as being the most common and most confusing of all the Anomma, demanding of revision when males of all forms were known.

It was described as occasionally found on Ghana cocoa, probably as "chance migrants", by Strickland (1951a).

Also later found throughout the Mampong Cemetery farm by Room (1971); and listed, as Anomma nigricans, from cocoa at Kade by Majer (1975, 1976b), with a single worker found in a pkd sample. One of the two species studied during 1971 by Gotwald (1974). He found it in all the areas he visited (coastal scrub, Guinea savannah and high forest). The main prey in the drier areas was insects (75%), mostly grasshoppers in the coastal area and a more mixed bag in Guinea savannah. In high forest areas, especially in and around cocoa at CRIG, the almost exclusive diet was earthworms.

In Nigeria, I found burmeisteri foraging at CRIN. Wheeler (1922) notes nigricans from Moor Plantation and Agege (by Lamborn).

Studied in Congo by Raignier and van Boven (1955), who calculated the egg production as 50,000,000 per year. Schneirla (1971) summarized many of their findings. He noted that it has been found at up to 3000 m asl in Sudan; the nests are 2-4 m below ground and the colony may be bigger than that of D. wilverthi. The periods of residence between migrations was longer than that of D. wilverthi, perhaps being more typical of the subgenus.

Working at Lamto, in the Ivory Coast, Leroux described colony size and nest habits; including an estimate of three colonies per 10 ha in the forest; and noted how among the principal predators are members of the subgenus Typhlopone and Odontomachus troglodytes (1977, 1979).

Numerous other records in Wheeler (1922), include Ivory Coast, Cameroun (many), and throughout tropical Africa. Wheeler, who provided the illustrations (left and on linked page) noted that the original descriptions (by Emery and Santschi had the largest morphs at TL 13 mm. The dichthadiigyne female (queen) discovered in Uganda measured 29 to 31 mm.