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 of worker and male specimens. 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
Borowiec (2016) - 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).

Male Aenictogiton males have distinctive wing venation where cross-vein cu-a in the fore wing arises proximal to M·f1, R·f3 is absent and is Rs·f3 ‘hanging’ free in the submarginal cell in the absence of Rs·f2. This, combined with the ‘army ant-like’ habitus that includes the lack of constriction between abdominal segments III and IV (no postpetiole), will serve to distinguish it from all other dorylines. The two other army ant genera that occur in the Afrotropics, Aenictus and Dorylus, do not have free Rs·f3 in fore wings.

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. (Borowiec 2016)

Biology
Borowiec (2016) - This Afrotropical genus was until recently known only from male specimens and little is known about its biology except that it is likely a subterranean nester and forager. Most records of males coming to light are associated with forest habitats (Brown 1975), except the savanna/woodland record from Namibia (Parr et al. 2003). The Ugandan workers collected in 2012 come from leaf litter sifted near a log in a moist evergreen forest in Kibale National Park. The mode of foraging, brood production, and colony life cycle remain unknown.

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
Known from workers and 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.

Borowiec (2016) - The taxonomic history of Aenictogiton begins with Emery’s description of Aenictogiton fossiceps, a male-based taxon that he placed in the Dorylinae (Emery 1901d). Subsequently, six other male-based species were described from the territory of Democratic Republic of the Congo. Santschi (1924) gave a key to all the species then known from males. The worker caste of Aenictogiton remained a mystery for over a century, until it was discovered in Uganda in 2008 and then collected again in 2012 in the same country. The genus has been most often collected from the Congo Basin (Brown 1975), although there are records from southern Angola, northern Namibia (Parr et al. 2003), and southwestern Kenya (Hita Garcia et al. 2009).

Aenictogiton is the sister taxon to Dorylus (Brady et al. 2006, Brady et al. 2014, Borowiec, in prep.).

Worker
Borowiec (2016) - Head: Antennae with 12 segments. Apical antennal segment moderately enlarged, broader than and about equal in length to two preceding segments combined. Clypeus without cuticular apron. Lateroclypeal teeth absent. Parafrontal ridges reduced. Torulo-posttorular complex vertical. Antennal scrobes absent. Labrum without median notch or concavity. Proximal face of stipes projecting beyond inner margin of sclerite, concealing prementum when mouthparts fully closed. Maxillary palps 1-segmented. Labial palps 1-segmented. Mandibles falcate, with teeth on elongated masticatory margin. Eyes absent. Ocelli absent. Head capsule with differentiated vertical posterior surface above occipital foramen. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Posterior head corners dorsolaterally immarginate. Carina surrounding occipital foramen ventrally absent. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Promesonotal connection with suture conspicuous and complete, but immobile. Pronotomesopleural suture visible, unfused up to notal surface. Mesometapleural groove deeply impressed, conspicuous. Transverse groove dividing mesopleuron absent. Pleural endophragmal pit concavity absent, but a minute pit present. Mesosoma dorsolaterally immarginate. Metanotal depression or groove on mesosoma absent. Propodeal spiracle situated high on sclerite. Propodeal declivity without distinct dorsal edge or margin and rectangular in posterior view. Metapleural gland with bulla visible through cuticle. Propodeal lobes absent. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, laterally above spiracle immarginate. Helcium in relation to tergosternal suture placed at posttergite and axial. Prora forming a simple U-shaped margin. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III anterodorsally immarginate and dorsolaterally immarginate. Abdominal segment III more than half size of succeeding segment IV, which is weakly constricted at presegmental portion (uninodal waist). Girdling constriction of segment IV present, i.e. pre- and postsclerites distinct. Cinctus of abdominal segment IV gutter-like and sculptured but not cross-ribbed. Abdominal segment IV not conspicuously largest segment. Abdominal tergite IV not folding over sternite, and anterior portions of sternite and tergite equally well visible in lateral view. Girdling constriction between pre- and posttergites of abdominal segments V and VI present. Girdling constriction between pre- and poststernites of abdominal segments V and VI present. Pygidium large, without impressed medial field, and simple, not armed with cuticular spines or modified setae. Hypopygium unarmed. Legs: Mid tibia with single simple/barbulate spur. Hind tibia with single pectinate spur. Hind basitarsus not widening distally, circular in cross-section. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland present as oval patch of whitish cuticle. Metabasitarsal gland absent. Hind pretarsal claws simple. Polymorphism: Apparently monomorphic.

Male
Borowiec (2016) - Head: Antennae with 13 segments. Clypeus without cuticular apron. Parafrontal ridges absent. Torulo-posttorular complex vertical, reduced small, single vertical carina. Maxillary palps 1-segmented. Labial palps 1-segmented. Mandibles falcate. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Carina surrounding occipital foramen ventrally absent. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Notauli absent. Transverse groove dividing mesopleuron absent but horizontal depression may be present. Propodeal declivity reduced, without distinct dorsal edge or margin. Metapleural gland opening absent. Propodeal lobes absent. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle immarginate. Helcium in relation to tergosternal suture placed at suture and axial. Prora simple, not delimited by carina. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III more than half size of succeeding segment IV; latter weakly constricted at presegmental portion (uninodal waist). Girdling constriction of segment IV absent, i.e. pre- and postsclerites indistinct. Cinctus of abdominal segment IV absent, not impressed. Girdling constriction between pre- and postsclerites of abdominal segments V and VI absent. Abdominal segment IV not conspicuously largest segment. Abdominal sternite VII simple. Ab-dominal sternite IX distally armed with two spines, with lateral apodemes about as long as medial apodeme, directed anteriorly (towards head); all apodemes very short. Genitalia: Cupula long relative to rest of genital capsule and shorter ventrally than dorsally. Basimere broadly fused to telomere, with no sulcus trace at junction, and ventrally with left and right arms abutting. Telomere expanded at apex. Volsella narrow, hook-shaped, occasionally forming two hooks at apex. Penisvalva laterally compressed, narrow and lance-shaped at apex. Legs: Mid tibia with pectinate and simple spur. Hind tibia with pectinate and simple spur. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland absent. Metabasitarsal glands absent. Hind pretarsal claws simple. Wings: Tegula present, broad, demiovate in shape. Vein C in fore wing present. Pterostigma broad. Abscissa R·f3 absent. Abscissae Rs·f2–3 present, disconnected from Rs+M. Cross-vein 2r-rs present, connected to Rs·f2–3&Rs·f4. Abscissae Rs·f4–5 differentiated into Rs·f4 and Rs·f5 by 2rs-m. Abscissa M·f2 in fore wing contiguous with Rs+M. Abscissa M·f4 in fore wing present, not reaching wing margin. Cross-vein 1m-cu in fore wing present. Cross-vein cu-a in fore wing present, arising from M+Cu and proximal to M·f1. Vein Cu in fore wing present, with only Cu1 branch prominent. Vein A in fore wing with abscissae A·f1 and A·f2 present. Vein C in hind wing absent. Vein Sc+R+Rs present. Vein R in hind wing present, extending past Sc+R but not reaching distal wing margin. Vein Sc+R in hind wing present. Abscissa Rs·f1 in hind wing present, contiguous with Rs·f2. Abscissa Rs·f2 in hind wing present, not reaching wing margin. Cross-vein 1rs-m in hind wing absent. Vein M+Cu in hind wing present. Abscissa M·f1 in hind wing present. Abscissa M·f2 in hind wing present. Cross-vein cu-a in hind wing present. Vein Cu in hind wing present. Vein A in hind wing with abscissae A·f1 and A·f2 present.

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.