Pogonomyrmex magnacanthus

An open desert species.

Identification
Key to North American Pogonomyrmex

Appears to be most closely related to Pogonomyrmex californicus, from which it differs in the worker caste chiefly by the larger eyes and generally much smaller stature and in the sexual castes by the enlarged eyes (Cole 1968).

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

Biology
Cole (1968) - All nests observed by the writer were in unshaded, rather loose, sandy soil of open desert, and each nest was surmounted by a circular, shallow, sand crater of 4 to 6 inches in diameter. Worker populations varied from about 100 to 225 per nest. The workers foraged diurnally at a rather slow and steady gait. They were docile and exhibited none of the usual erratic and rapid movements of Pogonomyrmex maricopa and Pogonomyrmex californicus when disturbed.

Nevada, Wheeler and Wheeler (1986) - Three nests had as superstructures downhill tailings below the entrance. Three had craters of fine sand 6-10 cm in diameter. The workers moved slowly. We have 13 records from 10 localities in Nevada, all from the Hot Desert in the southern portion of the state: 1,200-3,400 ft.

Nomenclature

 *  magnacanthus. Pogonomyrmex (Pogonomyrmex) magnacanthus Cole, 1968: 133, pl. 2, fig. 5; pl. 3, fig. 12; pl. 4, fig. 10; pl. 6, fig. 9; pl. 7, fig. 16; pl. 8, fig. 10; pl. 11, fig. 10 (w.q.m.) U.S.A. Taber, Cokendolpher & Francke, 1988: 51 (k.). See also: Johnson, Overson and Moreau, 2013: 205 (q.m.).

Worker
Holotype. (Cole Coll. No Cal-378). HL 1.34 mm, HW 1.36 mm, CI 101.5, 5L 1.00 mm, 51 73.5, EL 0.39 mm, EW 0.21 mm, OI 29.1, WL 1.48 mm, PNL 0.34 mm, PNW 0.36 mm, PPL 0.43 mm, PPW 0.54 mm.

Head length and width subequal. Eye very large, its greatest diameter equal to distance from its lower margin to mandibular insertion. Mandible as illustrated in Pl. III, Fig. 12; apical margin faintly and rather evenly convex; basal margin straight; masticatory border with 7 teeth irregular in size, shape, and spacing; apical tooth narrow, sharp, not much longer than subapical tooth which is subequal in size to first and third basals; second basal shorter than any aforementioned teeth; penultimate basal minute; ultimate basal distinctly larger than penultimate. Base of antennal scape as shown in Pl. IV, Fig. 10; shaft moderately, broadly, and evenly curved along basal half, not strongly compressed or flattened along the bend; basal enlargement rather weakly developed; superior lobe acute apically; superior declivity and inferior declivity not steep, meeting the shaft evenly at weak and broadly rounded angles; basal flange weak, very narrow, and thin, extending outward to just beyond apex of superior lobe; lip short, the margin very thin and curved slightly distad; longitudinal peripheral carina and point very weak; outer lateral margin of basal enlargement not impressed. Base of antennal scape similar to that of californicus but the lip shorter, thinner, and not curved so greatly distad.

Frontal area shining; bearing a strong, median, longitudinal carina. Cephalic rugae delicate, rather widely spaced, subparallel, longitudinal in front but diverging rather strongly and evenly into posterior corners of head and tending to form whorls above the eyes; finer and more closely spaced toward the eyes; those on occiput irregularly and arcuately transverse; interrugal spaces densely and finely punctate, subopaque. Median lobe of clypeus with sparse, delicate, widely and irregularly spaced, longitudinal rugae; interrugal spaces smooth and shining. Mandibles prominently, longitudinally rugose; interrugal spaces smooth and shining. Antennal scares smooth and shining.

Contours of thorax. petiole, and postpetiole as shown in Pl. VI, Fig. 9. Thorax strongly convex, mesoepinotal impression distinct; epinotum armed with a pair of weak angles, the broadly convex base notably longer than the steep, straight declivity. Thoracic rugae strong and rather widely spaced on mesonotum and epinotum, much finer on most of pronotum where they are largely obscured by fine, dense punctures; irregularly and widely spaced on pronotal collar; transverse on dorsum of pronotum, posterior portion of mesonotum, and base of epinotum; longitudinal on anterior portion o[ mesonotal dorsum; absent from declivous face of epinotum; interrugal spaces smooth and shining on pronotal collar, densely and finely punctate and somewhat shining on mesonotum and epinotum, very densely punctate and subopaque on sides of pronotum. Venter of petiolar peduncle and of postpetiole without a prominent process. Contours of petiolar and postpetiolar nodes, viewed from above, as illustrated in Pl. VII, Fig. 16; length and width of petiolar node subequal, the apex rather blunt, the surface finely and densely punctate and subopaque, the posterior portion with sparse, wavy, transverse striate; sculpture of postpetiolar node similar to that of a petiolar node.

Gaster densely and finely shagreened, moderately shining. Body a concolorous, medium, ferrugineous red.

HL 1.25-1.44 mm, HW 1.18-1.44 mm, CI 94.4-97.9, SL 0.95- 1.10 mm, SI 77.4-80.5, EL 0.38-0.46 mm, EW 0.23-0.68 mm, OI 29.8-31.9. WL 1.33-1.52 mm, PNL 0.30-0.42 mm, PNW 0.27-0.38 mm, PPL 0.34-0.46 mm, PPW 0.46-0.53 mm.

In some workers the epinotum is broadly and evenly rounded and devoid of armature, but in most specimens the epinotum is distinctly angulate and bears a pair of distinct tubercles or angles. The interrugal cephalic and thoracic punctures are more dense and prominent in some workers than in others, and hence the interrugal spaces vary in subopacity. I have assigned to this species a small series of workers collected by Dr. Creighton in the Inyo Mountains, California. These specimens differ from the types by having a prominent postpetiolar ventral process, but they agree very well otherwise. In a series of workers taken at a station fifteen miles west of Sentinel, Arizona, the cephalic and thoracic sculpture is everywhere very delicate, and the posterior corners of the head are very smooth and strongly shining.

Queen
Paratype. (Cole Coll. No Cal-424). HL 1.79 mm, HW 1.87 mm, CI 104.8, SL 1.22 mm, SI 65.2, EL 0.56 mm, EW 0.39 mm, OI 31.3, WL 2.67 mm, PNL 0.56 mm, PNW 0.60 mm, PPL 0.54 mm, PPW 0.88 mm.

Head, in lateral view, as shown in Pl. II, Fig. 5. Eye very large, its greatest diameter slightly more than distance from lower eye margin to mandibular articulation. Frontal area shining; with a strong, median, longitudinal carina. Caphalice rugae dense, rather fine, longitudinal on anterior part of head, strongly divergent from frons into occipital corners, forming whorls above the eyes, transversely arcuate on vertex and occiput; interrugal spaces smooth and shining; finely and faintly shagreened. Mandibles longitudinally rugose, the rugae broadly spaced, the interrugal spaces shining and finely shagreened.

Thoracic rugae longitudinal, fine, and dense on scutum and scutellum; coarser and transversely subparallel on pronotal collar; sparser and more widely spaced elsewhere on pronotum and on sides of mesonotum; rather coarse, widely spaced, and transverse on sides of epinotum; weaker, wavy, and more closely spaced on base of epinotum, absent from declivous face; interrugal spaces smooth, shining, faintly and finely shagreened. Epinotum withour armature, the base meeting the declivity at a well-rounded angle, the margins faintly carinate. Metanotum strongly acute medially. Metsternal angle with a prominent longitudinal carina. Venter of petiolar peduncle without a process. Petiolar node, viewed from above, with the length and width subequal, the apex broadly rounded and bearing small, distinct nipple; dorsum of node with a few, wavy, transverse rugules which are confined mostly to the midportion. Dorsum of postpetiolar node with sparse, wavy, transverse rugules confined to posterior portion, the interrugal spaces and remainder of node densely and finely shagreened and subopaque.

Gaster shining, very finely and densely shagreened. Body a concolorous brownish yellow; mandibles a little darker.

HL 1.71-1.82 mm, HW 1.79-1.90 mm, CI 104.4-104.7, SL 1.22-1.25 mm, SI 65.8-68.2, EL 0.53-0.57 mm, EW 0.34-0.38 mm, OI 31.0-31.3, WL 2.36-2.43 mm, PNL 0.38-0.42 mm, PNW 0.57-0.61 mm, PPL 0.49-0.57 mm, PPW 0.87-0.91 mm.

Male
Paratype. (Cole Coll. No. Cal-424). HL 1.25 mm, HW 1.37 mm, CI 109.6, SL 0.61 mm, SI 44.5, EL 0.65 mm, EW 0.38 mm, OI 52.0, WL 2.39 mm, PNL 0.46 mm, PNW 0.65 mm, PPL 0.53 mm, PPW 0.87 mm.

Eye very large, its greatest diameter about twice the distance from lower eye margin to mandibular articulation or about one-half the head length. Mandible as illustrated in Pl. VIII, Fig. 10; with 4, uneven, broad, sharp teeth arranged on a suboblique masticatory margin; apical tooth large and acute, subapical tooth narrower and notably shorter, the 2 basal teeth subequal in size, basalmost tooth distinctly offset from mandibular margin. Cephalic rugae longitudinal, rather weak, closely spaced, absent from clypeus and frontal area, irregular and broken behind the eyes; interrugal spaces faintly and finely punctured and rather shining. Scapes smooth and shiing, very finely shagreened.

Thorax and appendages mostly smooth and strongly shining, sides of thorax with a few weak striae; Mayrian furrows very weak; epinotum without armature. Petiole, postpetiole, and gaster very smooth and highly polished, not shagreened. Paramere of terminalia as shown in Pl. XI, Fig. 10.

Hairs pale golden yellow, long, flexuous, slender, pointed; abundant on head, scapes, legs, petiole, and postpetiole, somewhat sparser on thorax and gaster. Body a rather uniform, deep, rich brown except the appendages and petiolar peduncle which are lighter and the head which is mostly somewhat darker.

HL 1.14-1.14 mm, HW 1.25-1.25 mm, CI 109.7-109.7, SL 0.53-0.53 mm, SI 42.4-42.4, EL 0.61-0.61 mm, EW 0.38-0.38 mm, OI 53.5-53.5, WL 2.28-2.28 mm, PNL 0.38-0.42 mm, PNW 0.61-0.65 mm, PPL 0.46-0.49 mm, PPW 0.80-0.81 mm.

Type Material
Palm Springs, California; holotype and paratype workers, Cole Coll. No. Cal-378, August 8, 1960; paratype workers, same date, Cole Coll. Nos. Cal-375, 376, 377, 379, 382, 383; paratype workers, August 7, 1961, Cole Coll. No. Cal-407, 408, 409, 410; paratype workers, females, and males, June 13, 1963, Cole Coll. Nos. Cal-424, 425, 426, 427, 428, 429.