Neivamyrmex nigrescens

This common species is by far the most widespread species in the United States. As a result of this wide range it is also by far the most studied and best known of the Neivamyrmex.

Identification
Key to the Neivamyrmex species of the United States

Distribution
United States: transcontinental across southern states, north to West Virginia, Tennessee, Colorado and Nebraska; Mexico: Baja California, Nayarit, Oaxaca, Sonora (Watkins, 1982).

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Mexico.

Habitat
N. nigrescens shows an extremely wide habitat range. Rarely encountered in desert environments it is nonetheless present, apparently largely confined to canyons and hillsides. Ward (1999) listed the elevational range from sea level to 1460m in California, but we have records up to 2200m in areas outside of California. (Snelling and Snelling 2007)

Biology
Snelling and Snelling (2007) :

Colonies studied by Wheeler (1900) consisted of “thousands” of individuals, while Schneirla (1958) estimated 150,000 to 250,000 workers per nest. Neivamyrmex nigrescens has a nomadic/statary cycle like Neotropical army ants such as Eciton. The nomadic phase of the cycle begins when pupae eclose to workers. The whole colony then moves along a trail, usually during night hours, capturing any insects they encounter and raiding the nests of other ant species encountered. Columns may be 90m long and are headed by scouts. The colony bivouacs before dawn, using natural cavities or nests of other species, which they have pillaged. The following night they again move and raid. This nomadic cycle lasts for about three weeks or until the larvae in the colony (which they transport each night) begin to pupate. The statary phase then begins and the ants nest in subterranean cavities, either under stones or in abandoned ant nests for about 18 days (Schneirla, 1958). Raids continue but are less extensive than during the nomadic phase.

New colonies of N. nigrescens are formed when “a daughter queen leaves the parental nest, accompanied by a number of workers. A mature colony is capable of producing a small number of females, some of which may be fertilized in the nest by their brothers, but this does not preclude mating outside the nest, or with males of other colonies. Since females are never winged, they can make no nuptial flight.” (Smith 1965). Recent very preliminary data for this species suggest that N. nigrescens may, at least at times, have more than one functional queen present in the colony.(D. Kronauer, pers. comm.)

Other ants form an important part of the diet of N. nigrescens. Mallis (1938) observed this species carrying larvae and pupae of Tetramorium caespitum (Linné), as well as click beetles, mayflies, water boatmen and crickets. Wheeler & Long (1901) found larvae of Solenopsis geminata (Fabr.) and three species of Pheidole, as well as dead carabid beetles, in nests they studied in Texas. Ward (1999) further notes that in California Messor andrei (Mayr), Pheidole californica Mayr, Pheidole hyatti Emery, Solenopsis molesta (Say) and Formica moki Wheeler are also prey items of this species. In Arizona N. nigrescens has been observed regularly raiding Pheidole obtusospinosa Pergande (as P. subdentata) and Pheidole desertorum Wheeler. Neece & Bartell (1982) noted the presence of unidentified mites of the family Trachyaropodidae in colonies of N. nigrescens. The blind snake, Leptotyphlops dulcis, is able to follow the pheromone trails of N. nigrescens to locate columns and feed on the ant brood (Watkins et al., 1967). When the army ants attack the snake it forms a protective ball-like coil and smears a cloacal fluid on its body, which discourages further ant attacks (Watkins et al., 1972).

Several species of scuttle flies (Diptera: Phoridae) are known to parasitize adults of N. nigrescens. These include species in the genera Dacnophora and Cremersia (B. V. Brown, pers. comm.), and Xanionotum (Rettenmeyer and Akre 1968). The diapriid wasp, Ecitovagus gibbus Masner has been found as a parasitoid of N. nigrescens in southeastern Arizona (Masner 1977). Myrmecophilous Staphylinidae (Coleoptera) associated with this ant in areas other than California include: Microdonia laticollis Brues, M. nitidiventris Brues, M. occipitalis Casey, Ecitoxenidia brevicornis Seevers, E. brevipes Brues, Dinocoryna carolinensis Seevers, and Ecitonidia wheeleri Wasmann (Seevers 1965). At least two species in the carabid beetle genus Helluomorphoides (H. ferrugineus Casey and H. latitarsis LeConte) are specialized predators on both the booty and brood of N. nigrescens in southeastern Arizona: “The beetles were observed running in army ant columns or standing off to the sides of the columns, behind rocks or beneath clusters of leaf litter. During their predatory activities, beetles ran along the trails in both directions, 'plowing' through the continuous two-way ant traffic. When a beetle of either species contacted a worker ant bringing booty back to her bivouac, the ant usually dropped the booty. On some occasions, if the booty was a larval or pupal individual of another ant species, the beetle immediately ate it and continued on the trail. On other occasions the beetle picked up the dropped booty, left the raiding column, and proceeded to a nearby rock. There, the beetle quickly ate the larva or pupa, returned to the column, and resumed running along the trail” (Topoff, 1969). Beetles were observed to forcibly take booty from the ants. The beetles were also seen to feed on brood caches of the Neivamyrmex colony with which they became associated.

For further information on the biology and behavior of this species, see Ward (1999).

Nomenclature

 *  nigrescens. Labidus nigrescens Cresson, 1872: 194 (m.) U.S.A. Wheeler, W.M. 1900a: 563 (q.); Smith, M.R. 1942c: 551 (w.); Wheeler, G.C. & Wheeler, J. 1984: 273 (l.). Combination in Eciton: Dalla Torre, 1893: 5; in E. (Labidus): Emery, 1895c: 261; in E. (Acamatus): Emery, 1900a: 187; in E. (Neivamyrmex): Smith, M.R. 1942c: 550; Gregg, 1963: 286; in Neivamyrmex: Borgmeier, 1955: 494; Watkins, 1972: 349. Senior synonym of schmitti: Smith, M.R. 1938b: 160; Borgmeier, 1955: 494. See also: Watkins, 1972: 358; Smith, D.R. 1979: 1331; Petralia & Vinson, 1980: 378; Ward, 1999a: 84; Snelling, G.C. & Snelling, R.R., 2007: 484.
 * schmitti. Eciton (Acamatus) schmitti Emery, 1894c: 183 (diagnosis in key) (w.) U.S.A. Emery, 1895c: 258 (w.); Wheeler, W.M. & Long, 1901: 161 (m.); Wheeler, G.C. 1943: 331 (l.). Junior synonym of nigrescens: Smith, M.R. 1938b: 160; Borgmeier, 1955: 494.