Neivamyrmex

Army ants that prey on ants and termites. Subterranean in their existence, a few Neivamyrmex species are more commonly collected than others because they will occasionally have portions of their raids, or raiding trails, above ground or their workers are found under stones. Borowiec (2016) - Neivamyrmex is the most species-rich and widely distributed genus of New World army ants. The biology of the vast majority of the more than 100 described species is unknown, but Neivamyrmex nigrescens has become one of the best studied dorylines.

Identification
Borowiec (2016) - Worker Neivamyrmex have 12-segmented antennae, propodeal spiracle high on the sclerite, lack conspicuous propodeal lobes, pygidium small and without a central impressed field, waist two-segmented, and pretarsal claws without a tooth. The simple claws distinguish Neivamyrmex workers from all other New World army ant genera (Cheliomyrmex, Eciton, Labidus, and Nomamyrmex). Aenictus in the Old World will also match some of these diagnostic characters but workers of this genus never have more than 10 antennal segments.

Male Neivamyrmex males share the army ant-like habitus with other members of the Eciton genus-group. See discussion under Cheliomyrmex male diagnosis for characters differentiating New World army ant males from those of the Old World. Among the New World army ants, Neivamyrmex can most reliably distinguished by a combination of apex penisvalvae without setae, no dense setation on gaster, and abdominal segment II (petiole) without a deeply notched or concave surface. The bare penisvalvae are shared only with Eciton and Nomamyrmex but the former always has a deeply excavated petiole and the latter has conspicuous tufts of dense setae on the gaster.

Distribution
Central and southern United States, south to central Argentina.

Biology


Borowiec (2016) - The majority of species has never been studied in any detail, and much of what we know comes from the observations made on one relatively common species, Neivamyrmex nigrescens, studied extensively by Howard Topoff and his students (Gotwald 1995). The biology of other species has been summarized by Rettenmeyer (1963). If N. nigrescens is representative of this genus, the lineage’s habits are similar to those of other New World army ants. There are marked nomadic and statary phases, lasting about 16 and 20 days, respectively. The colonies are of moderate size, containing 80,000 to 140,000 workers (Rettenmeyer 1963; Topoff et al. 1980 estimate 10,000–50,000) and bivouacs are subterranean. The prey consists of almost exclusively other ants’ brood.

Nesting sites of Neivamyrmex are rarely observed. Rettenmeyer (1963) reported that although known bivouac sites of N. nigrescens in Kansas are typically at least 1 meter below the surface, two bivouacs were discovered that were completely contained within the upper 30 cm of the soil. Emigration behavior in this species has been very well described. Environmental factors, such as prey availability/density and nest site availability, influence the emigration behavior (Topoff and Mirenda 1980, Mirenda and Topoff 1980). Neivamyrmex carolinensis and Neivamyrmex kiowapache are unusual among army ants in that they are the only species known to be polygynous, with colonies reported to contain over a dozen queens (Rettenmeyer and Watkins 1978, see also Snelling and Snelling 2007). The queens of N. kiowapache have been shown to mate with much lower frequency than other army ants. This is in accordance with the prediction that the costly multiple matings will be reduced or lost if genetic diversity of workers can be achieved through polygyny (Kronauer and Boomsma 2007b).

The foraging biology of N. nigrescens in Arizona was studied in detail by Mirenda et al. (1980). They reported that these army ants forage at night and raid nests of many other ants and termites. The ants in the genus Pheidole were shown to be the preferred prey, being taken twice as often as expected based on colony density. Pogonomyrmex, Forelius, and Myrmecocystus were reported to be avoided. The authors observed temporal variation in prey composition, noting that as the season progressed and conditions became drier, many of the prey Pheidole species ceased activity and sealed their nests. Neivamyrmex nigrescens was then observed to rely more heavily on Novomessor cockerelli as prey. Several Neivamyrmex species can occur sympatrically, and it is likely that a diversity of prey preferences exists in the genus. Mirenda et al. (1980) also observed multiple raids of Neivamyrmex harrisii, sympatric with N. nigrescens, and noted that Solenopsis xyloni was the only species being attacked. Neivamyrmex nigrescens uses both tactile and chemical cues in orientation (Topoff and Lawson 1979).

Many species of ants respond to a Neivamyrmex attack by nest evacuation and this behavior has been highlighted as a tool for collecting colonies of soil-nesting species that are normally difficult to excavate. Smith and Haight (2008) showed that 150-300 Neivamyrmex nigrescens workers poured into the nest entrance of Novomessor cockerelli induced evacuation of a mature colony, including brood and queen.

Nomenclature

 *  NEIVAMYRMEX [Ecitoninae: Ecitonini]
 * Neivamyrmex Borgmeier, 1940: 606 [as subgenus of Eciton]. Replacement name for Acamatus Emery, 1894c: 181. [Junior homonym of Acamatus Schoenherr, 1833: 20 (Coleoptera).]
 * Neivamyrmex raised to genus: Borgmeier, 1950c: 624.
 * Neivamyrmex senior synonym of Woitkowskia: Borgmeier, 1955: 277.
 * ACAMATUS [junior homonym, see Neivamyrmex]
 * Acamatus Emery, 1894c: 181 [as subgenus of Eciton]. Type-species: Eciton (Acamatus) schmitti (junior synonym of Labidus nigrescens), by subsequent designation of Ashmead, 1906: 24; Wheeler, W.M. 1911f: 157. [Junior homonym of Acamatus Schoenherr, 1833: 20 (Coleoptera).]
 * Neivamyrmex Borgmeier, 1940: 606, replacement name for Acamatus Emery.
 * WOITKOWSKIA [junior synonym of Neivamyrmex]
 * Woitkowskia Enzmann, E.V. 1952: 443. Type-species: Woitkowskia connectens (junior synonym of Labidus walkerii), by original designation.
 * Woitkowskia junior synonym of Neivamyrmex: Borgmeier, 1955: 277.

Taxonomic Notes
Borowiec (2016) - The first species now classified in Neivamyrmex were described from males by William Shuckard in his 1840 series ‘Monograph of the Dorylidae’. Borgmeier later erected the genus (Borgmeier 1940) and cemented its future use with his classification of New World army ants presented in his monographs (Borgmeier 1953, 1955). Borgmeier (1955) also presented an internal classification for the genus with fourteen informal species groups, including five based solely on males as, typically for army ants, numerous names have been proposed for males without associations with workers. Later work on Neivamyrmex taxonomy has been dominated by Julian Watkins who published many new isolated species descriptions and also provided updated identification resources for this and other New World army ant genera, first for New World in general (Watkins 1976) and later for United States in particular (Watkins 1985). This latter resource was recently updated with a publication by Snelling and Snelling (2007). Neivamyrmex is the most species-rich of the Eciton genus-group with 127 extant species. The genus is the sister group to the clade of the other four New World army ant genera and is monophyletic (Borowiec, in prep.). There is no comprehensive internal phylogeny, but preliminary data indicates that some of the species groups proposed by Borgmeier are not monophyletic (Borowiec, in prep.).

Worker
Borowiec (2016) - Head: Antennae with 12 segments. Apical antennal segment not enlarged, not broader and longer than two preceding segments combined. Clypeus with cuticular apron. Lateroclypeal teeth absent. Parafrontal ridges reduced. Torulo-posttorular complex vertical. Antennal scrobes absent. Labrum with median notch or concavity. Proximal face of stipes projecting beyond inner margin of sclerite, concealing prementum when mouthparts fully closed. Maxillary palps 2-segmented. Labial palps 3- or 2-segmented. Mandibles triangular, with teeth. Eyes absent or present, composed of few poorly defined ommatidia. Ocelli absent. Head capsule with differentiated vertical posterior surface above occipital foramen; differentiation sometimes weak. 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 or separated by ridge that is low on pronotum. Promesonotal connection with suture completely fused or suture weakly differentiated, immobile. Pronotomesopleural suture completely fused or unfused partway to notal surface. Mesometapleural groove not impressed to weakly impressed. Transverse groove dividing mesopleuron absent or present. Pleural endophragmal pit concavity present. Mesosoma dorsolaterally immarginate. Metanotal depression or groove on mesosoma absent. Metanotal depression or groove on mesosoma present. 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 present, short. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle immarginate. Helcium in relation to tergosternal suture placed at posttergite and axial. Prora forming a simple U-shaped margin or V-shaped protrusion. Spiracle openings of abdominal segments IV–VI circular, oval, or slit-shaped. Abdominal segment III anterodorsally immarginate and dorsolaterally immarginate. Abdominal segment III about half size of succeeding segment IV, which is strongly constricted at presegmental portion (binodal 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 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 absent. Girdling constriction between pre- and poststernites of abdominal segments V and VI absent. Pygidium small, reduced to narrow strip, without impressed medial field and simple, usually not armed with cuticular spines or modified setae but occasionally with one or two pairs of thick modified setae. Hypopygium unarmed. Legs: Mid tibia with single pectinate 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 absent to conspicuous patch of whitish cuticle occupying at least half of tibia length. Metabasitarsal gland absent. Hind pretarsal claws simple. Polymorphism: Monomorphic to polymorphic.

Queen
Borowiec (2016) - Dichthadiiform, blind or with very small eyes, without ocelli. Known for several species. See e.g. Watkins (1972) and Wheeler (1921) for descriptions and illustrations of Neivamyrmex gynes.

Male
Borowiec (2016) - Head: Antennae with 13 segments. Clypeus without cuticular apron. Parafrontal ridges absent. Torulo-posttorular complex vertical. Maxillary palps 2-segmented. Labial palps 3- or 2-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. Propodeal declivity reduced, without distinct dorsal edge or margin. Metapleural gland opening absent. Propodeal lobes absent or present. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle immarginate. Helcium in relation to tergosternal suture placed at posttergite and axial. Prora simple, not delimited by carina. Spiracle openings of abdominal segments IV–VI oval or slit-shaped. 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. Abdominal sternite IX distally armed with two spines, often with additional projections such as medial spine or paired median denticles, with lateral apodemes longer than much reduced medial apodeme, directed anteriorly (towards head). Genitalia: Cupula very long, nearing or surpassing length of rest of genital capsule and of approximately equal length on both dorsal and ventral surfaces. Basimere narrowly fused to telomere, with sulcus visible at least partway through junction, and ventrally with left and right arms abutting. Telomere expanded at apex. Volsella narrow, hook-shaped or laterally flattened, triangular in lateral view, narrowing towards tip. Penisvalva not flattened at apex, expanded. Legs: Mid tibia with single pectinate spur. Hind tibia with single pectinate spur. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland absent. Metabasitarsal glands absent. Hind pretarsal claws simple or each armed with a tooth. Wings: Tegula present, broad, demiovate in shape. Vein C in fore wing present. Pterostigma broad. Abscissa R·f3 present, running toward distal wing margin and enclosing cell with Rs·f5. Abscissae Rs·f2–3 present, connecting with Rs+M&M·f2. Cross-vein 2r-rs present, differentiated from Rs·f4 by presence of Rs·f2–3. Abscissae Rs·f4–5 differentiated into Rs·f4 and Rs·f5 by 2rs-m. Abscissa M·f2 in fore wing present, separated from Rs+M by Rs·f2. Abscissa M·f4 in fore wing present, reaching wing margin. Cross-vein 1m-cu in fore wing present. Cross-vein cu-a in fore wing present, arising from Cu and distal to, at or near M·f1. Vein Cu in fore wing present, with both branches Cu1 and Cu2. Vein A in fore wing with abscissae A·f1 and A·f2 present. Vein C in hind wing present. Vein R in hind wing present, reaching distal wing margin. Vein Sc+R in hind wing present. Abscissa Rs·f1 in hind wing present, shorter than 1rs-m. Abscissa Rs·f2 in hind wing present, reaching wing margin. Cross-vein 1rs-m in hind wing present, about as long as M·f1. 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.

Larvae
Borowiec (2016) - Described in Wheeler and Wheeler 1984.