Aenictogiton

Hita Garcia, Wiesel and Fischer (2013) - The genus occurs in Central, South, and East Africa and is biogeographically limited to the Afrotropical region (Brown, 1975; Parr et al., 2003; Hita Garcia et al., 2009). Material of Aenictogiton is generally scarce, and consists solely of male specimens. Brown (1975) already stated the complete lack of knowledge concerning the female castes, which, despite intensive search efforts, have not been discovered until the present day. The known species richness appears comparatively small, with just seven described species (Brown, 1975), although a good number of unidentifiable and possibly undescribed specimens located in several museum collections await taxonomic examination and possibly description as new species. The taxonomy of the genus can be regarded as unsatisfactory since it was never revised after the initial species descriptions (Emery, 1901; Forel, 1913; Santschi, 1919b, 1924).

Identification
Diagnosis. Worker. The workers of the one Aenictogiton species for which this caste is known so far are unique in having propodeal spiracles situated high on the sclerite and propodeal lobes reduced, pygidium large but not armed with modified setae, and possessing marked constrictions between abdominal segments IV, V, and VI. Small body size is also characteristic, with mesosoma length under 0.65 mm in the only species known from workers. The same characters will serve to distinguish Aenictogiton from other Afrotropical dorylines that either have spiracles situated low on the propodeum, propodeal lobes well-developed and pygidium armed (Eburopone, Lioponera, Ooceraea, Parasyscia, Zasphinctus) or are markedly larger and have at most weakly impressed abdominal sternites at junction of segments IV, V, and VI, never conspicuous constrictions on both tergites and sternites (Aenictus, Dorylus).

Distribution
This is an exclusively Afrotropical lineage and most species have been described from the Congo Basin but records extend to southern and eastern Africa.

Species richness
Species richness by country based on regional taxon lists (countries with darker colours are more species-rich). View Data



Biology
Brown (1975) - To my knowledge, the only material of Aenictogiton found in collections consists of winged males taken at light. At least some of these samples were taken in or near forest or gallery forest, but I do not know the setting of many of the label localities. The habitus of these males certainly is generally like that of some army ants, though they are somewhat smaller than most army ant males. The tufts and fringes of long, golden hairs suggest the similar arrangements (“trichomes,” etc.) in many army ant males and in formicid and other insect inquilines in ant nests, and lead naturally to speculation that these males may be adapted towards gaining entrance to colonies of their own or another host species by attracting and offering the host workers allomones that convert or lull their aggressive behavior toward strangers. The army ant males must gain access to alien conspecific colonies to mate with their queens. But the inquiline males must achieve acceptance into the host species' colony in order to work their parasitic mischief.

To me, Aenictogiton males have a habitus much like that of the known army ants of the same caste. It is not beyond belief that they could be parasites, but then one would expect to find winged or dealate queens that corresponded to them, and no such queens have been seen. In fact, the lack of queens in collections suggests that they may be wingless and ergatoid or dichthadiiform, as in army ants. The males of Aenictogiton lack metapleural gland openings, as do army ant males of all genera, and also some parasitic ant groups.

Garcia, Wiesel and Fischer (2013) - The biology of this enigmatic genus remains an almost complete mystery. Brown (1975) mentioned the possibility that these ants are subterranean or otherwise strongly cryptobiotic; we fully agree since no foraging worker nor any trace of a colony could ever be found. Phylogenetic and morphological affinities to the army ant genus Dorylus suggest an army-ant-like lifestyle, although there is no current evidence for this. However, most males were collected from light traps close to forest localities, indicating that Aenictogiton might prefer forested habitats.

Castes
Only known from males. Finding a colony of one of the species in this enigmatic genus is surely on the top ten list of "ants that need to be found."

Nomenclature

 *  AENICTOGITON [Aenictogitoninae]
 * Aenictogiton Emery, 1901d: 49. Type-species: Aenictogiton fossiceps, by monotypy.

Male
Brown (1975) - Long (TL 5-9 mm), slender insect with hypognathous head and long, subcylindrical, downcurved gaster; prevailingly smooth and shining, with some punctate areas; color basically tawny yellow (testaceous to yellow ferruginous).

Head somewhat depressed dorsoventrally; as seen full-face oblong, longer than broad without the huge compound eyes, but broader than long if the eyes are included; posterior angles sharply rounded, posterior margin concave, and sides straight or weakly convex, parallel or weakly converging or diverging posteriad. Compound eyes very large and bulging, their anterior margins reaching the mandibular insertions, occupying half or more of the sides of the head; inner margins convex; surfaces beset with short, fine, erect hairs. Front of head between eyes deeply concave; clypeus indistinguishably fused with cranium; antennal sockets close together, contiguous to anterior margin of head, which is essentially straight (more or less feebly sinuate), or concave and transverse. Frontal carinae completely fused and reduced to an inconspicuous carina that extends posteriad only a short distance between the antennal sockets before disappearing. Ocelli very large and prominent, set in partial sockets; immediately behind them is a deep and wide pit that is peculiar to Aenictogiton. Mandibles wide falciform, inserted far apart, tapering and curving evenly inward to acute apices that overlap at full closure, leaving a wide space between the more basal parts of the shafts; inner margins toothless and cuitra,e. Antennae 13-merous, rather small and weak for insects of this size; scapes short, incrassate towards their apical halves, about equal to the combined first 5 funicular segments in length, but not reaching much beyond the mid length of the compound eyes when laid back. All funicular segments longer than broad except possibly IV-VII, one or more of which may be as broad as, or slightly broader than, long; pedicel clavate, nearly as long as the next 2 (II and III) funicular segments combined; funiculus distinctly incrassate in its apical 2/3; apical segment longest, but somewhat compressed in dry specimens.

Trunk elongate (2.3-2.6 times longer than wide), especially the pronotum and scutum; the latter takes up much more than half the truncal length. Notauli lacking; long, fine parapsidal furrows present but inconspicuous; in dried specimens, the scutum is usually partly buckled, so that an elongate concave area appears on either side of the dorsal midline. Scutellum simple, convex; metanotum forming a narrow transverse belt; propodeum rounded in both directions. Sides of pronotum and lower posterior half of trunk with broad and fairly deep hollows or sulci, which may be partly due to collapse of the thin integument. Since these hollows are present and similar in 8 specimens belonging to at least 2 species, I assume that they are spaces to accommodate the upfolded legs when the insect is being carried by workers or is feigning death. The pleura are unbroken by long sutures of any kind, except for the complete and strongly oblique one between the pronotum and sides of the mesothorax. Propodeal spiracle small and inconspicuous, situated below mid-height of the trunk; metapleural gland bulla and meatus apparently absent, or at least not visible from ordinary external views.

Wings long and broad, the forewing about as long as the body (minus the head), or longer, with primitive ponerine venation, except for the following: Rsf2.3 detached at base from Rs + M; rarely Rsf2.3 is curved posteriad and weakly attached to Mf3, but usually its base is floating free. Mf1, though rather strongly oblique, originates well distad of cu-a. Pterostigma large, thick, and heavily pigmented. In the hindwing the anal lobe is lacking, and, although Rs and M are both usually present, r-m is completely absent. Hamuli inconspicuous, 8-12 (8 specimens examined). Occasionally stubby adventitious veins are found in the forewing, usually issuing posteriad from longitudinal veins. Crossvein cu-a is sometimes weak or absent in the hind wing.

Legs moderate in length; middle and hind coxae very deeply sulcate dorsally, and sharp genual edges are formed on either side of the cleft. Femora laterally compressed but broadened in the extensor-flexor plane, narrowing basad; their flexor edges with a variably extensive apical groove to receive the folded tibia. Tibiae sub clavate, broadest in the distal half, the middle and hind pairs all bearing a narrowly pectinate spur and usually a smaller setiform spur. Tarsal segments slender; claws slender, simple.

Petiole special in shape, depressed, subtrapezoidal, longer than wide to wider than long according to species, with concave anterior margin and slightly produced anterior corners; broadest behind and with prominent, often subacute posterior corners; dorsal face convex in front, but with a broad, shallow median sulcus crossing the summit from the front and widening behind to produce a deep subtriangular excavation that occupies much of the posterior half of the surface. From side view, the petiole is convex above, highest in the anterior half, with rounded front and rear corners; sides rounded and bulging; subpetiolar process a laterally compressed keel with curved outline, steep in front and tapering caudad.

Postpetiole incorporated with gaster, and not separated from gaster by any constriction. As seen from above, the postpetiole tapers anteriad and is narrowly rounded in front (the narrowly rounded tergal portion overhangs the sternum in front). Remaining gastric segments (true abdominal somites IV through VII) cylindrical, slightly wider than long, subequal among themselves. Postpetiolar tergum and sternum solidly fused; in succeeding segments, terga and sterna are unfused and readily separable. Pygidium (tergum VIII) rounded but not enlarged, with an apical rim; hypopygium forming a robust, slightly upcurved fork with acute, convex-sided prongs and a short, constricted, stalk-like base. Genital capsule partly retractile, with large, expanded, shell-like parameres, a similunar, non-serrate aedeagus, and small volsella-lacinia differing in shape with the species.

Pilosity consisting of 3 types of hairs: (1) long, fine, flexuous, golden hairs bunched in tufts or rows on mandibles, clypeal margin, scapes, front half of dorsal surface of head and underside of head, along posterodorsal and posterolateral margins of pronotum, along posterior margin of scutum, on sides of mesothorax, on scutellum, on sides of propodeum and posterior corners of petiole, on underside of petiole and subpetiolar process, on femora, tibiae, and hind coxae, and on apex of gaster and terminalia; (2) short to long, appressed to decumbent, straight or slightly curved, golden hairs investing gaster like a coarse pubescence; (3) very short, fine, curved, erect to suberect hairs forming a sparse but rather even cover on upper (posterior) part of head, outer margins of mandibles, scutal surface, coxae, propodeal dorsum, petiolar disc, tarsae, and antennal funiculi.