Neivamyrmex melanocephalus

Snelling and Snelling (2007) - This rather large distinctive species is only rarely encountered in the United States and its principal range lies in Mexico and Guatemala. One foraging raid of N. melanocephalus was observed. It occurred in full daylight and the workers were taking a variety of small arthropods (B. V. Brown, pers. comm). We believe that Neivamyrmex mandibularis is the likely male of N. melanocephalus, but it is also possible that N. mandibularis could be the opposite sex of Neivamyrmex graciellae.

Identification
Key to the Neivamyrmex species of the United States

Smith (1942) - The major worker of melanocephalum can be readily distinguished by the form of the mandibles; size and shape of the scape; conspicuous eyes; rounded posterior comers of the head; the contrast in color and sculpture of head and gaster as compared with thorax; sculpture of pronotum; and the form of the petiole and postpetiole.

The color of the thorax varies considerably, ranging from light yellowish brown through deeper reddish brown to almost blackish; the color seems more variable in smaller workers than in the larger workers. The sculpture of the thorax also varies greatly, being much more rough in some individuals than in others. The head of the smaller worker is uniformly longer and narrower than the head of the major worker.

The major worker is most likely to be confused with that of pilosum. It may be distinguished, however, by the different color and sculpture of the thorax; the more weakly arched pronotum; and the weakly developed tooth on the petiolar peduncle; which is never so large or acute, or directed so far posteriorly, as that of pilosum.

Distribution
United States: Arizona; Mexico: south at least to Oaxaca and Morelos.

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

Castes
Known only from the worker caste.

Nomenclature

 *  melanocephalus. Eciton melanocephalum Emery, 1895c: 260 (footnote) (w.) MEXICO. Combination in E. (Neivamyrmex): Smith, M.R. 1942c: 549; in Neivamyrmex: Borgmeier, 1953: 6. Senior synonym of xipe: Smith, M.R. 1942c: 549; Borgmeier, 1953: 19. See also: Borgmeier, 1955: 385; Snelling, G.C. & Snelling, R.R., 2007: 479.
 * xipe. Eciton (Acamatus) melanocephalum subsp. xipe Wheeler, W.M. 1914b: 41 (w.) MEXICO. Junior synonym of melanocephalus: Smith, M.R. 1942c: 549; Borgmeier, 1953: 19.

Worker
Smith (1942) - Major. Length 4.5-5.5 mm.

Head approximately as broad as long; broadest anteriorly; with convex sides and very weakly emarginate posterior border. Eye ocelluslike, very distinct against black background of head. Mandible rather large, subtriangular, with well-defined superior, inferior, and masticatory borders; superior border without any distinct excision or protuberance. Antennal scape large, curved; exceeding posterior border of eye by at least its greatest width; all segments of funiculus distinctly longer than broad. Promesonotum, in profile, very feebly arched; meso-espinotal constriction weakly developed. Thorax without dorsal sutures. Pronotum with very small but distinct transverse carina. Petiole longer than broad, with somewhat abrupt posterior surface and a more gently sloping anterior surface; anterior surface constricted before its termination at the thorax. Legs rather long. Petiolar peduncle with very small anteroventral tooth, which is directed more ventrad than posteriorly. Postpetiole broader than petiole, subtrapezoidal, broader posteriorly than anteriorly, with convex sides and straight anterior end.

Head, dorsal surface of petiole and postpetiole, and gaster smooth and shining; mandibles, funiculi, thorax, and tarsi subopaque or opaque. Mandibles longitudinally striated, with scattered piligerous punctures. Head highly polished, bearing very small, scattered, piligerous punctures. Thorax covered with dense, granular punctures, which are interspersed with foveolae; meso- and metapleura more coarsely sculptured, the sculpturing of a rugose-reticulate nature; pronotum longitudinally rugulose.

Body with numerous suberect to erect, yellowish hairs of unequal length, some of which are unusually long.

Head and gaster almost black. Mandibles, anterior border of head, thorax, legs, petiole, and postpetiole of a much lighter reddish brown.

Type Material
Smith (1942) - Tepic, Mexico. Cotypes in the United States National Museum.