Pogonomyrmex desertorum

This is a species of seed harvesters (individual and group forager) with small nest populations (few hundreds?). They are very docile ants. They nest in sandy areas, or even gravel soils, with a small mound surrounding the nest entrance. Flights occur in June and July. During the mating flights, sexuals search for the highest object in an area, which in its typical habitat is usually the myrmecologist! It can be a very interesting experience, and additionally the females can deliver a painful sting. (Mackay and Mackay 2002)

Identification
Cole (1968) - In the eastern part of its range, Pogonomyrmex desertorum is pale ferrugineous red; the pronotal rugae are delicate and comparatively sparse so that the highly shining surface is well revealed; and the posterior corners of the head are strongly shining and free of sculpture. This combination of characters defines the "typical" desertorum as it occurs in western Texas and in comparable areas of Mexico. With westward progression there is a gradual intensification and some addition of pronotal rugae, so that smaller areas of the shining body surface are exposed. Coincident with this transition is a deepening of body color and a reduction in extent of the smooth and shining corners of the head. In the extreme western portion of the range of destertorum, the pronotal rugae are more numerous and coarser; and the cephalic rugae have encroached for such a considerable distance into the posterior corners of the head that some workers of a nest series may have these parts almost completely covered with very fine rugae which are sufficiently dense to obscure almost entirely the shining surface. These features, together with a rather deep ferrugineous red hue, prevail in collections from stations near Gila Bend, Arizona, and Needles, California.

Distribution
United States: western Texas, southern New Mexico, southern Arizona. Mexico: northern Tamaulipas, San Luis Potosi, Durange, Coahuila, Chihuahua, Sonora.

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

Habitat
Chihuahuan Desert in rocky or sandy soils, including dunes. (Mackay and Mackay 2002)

Biology
The ants nest in sand or very sandy soil in open areas and construct circular craters of the same material. The workers move slowly, forage on trails at a steady gait, and frequently have the gaster turned downward as though they were laying a chemical trail. When disturbed at the nest they retreat and crawl beneath covering material if available. They are extremely docile; I have never been able to elicit an attack response. In fact, desertorum is probably the most inoffensive species of all North American members of its subgenus. (Cole 1968)

Nomenclature

 *  desertorum. Pogonomyrmex desertorum Wheeler, W.M. 1902c: 387 (w.) U.S.A. Cole, 1968: 67 (q.m.); Taber, Cokendolpher & Francke, 1988: 51 (k.). Senior synonym of ferrugineus: Cole, 1968: 65.
 * ferrugineus. Pogonomyrmex desertorum var. ferrugineus Olsen, 1934: 506 (w.) U.S.A. Subspecies of desertorum: Creighton, 1950a: 124. Junior synonym of desertorum: Cole, 1968: 65.

Worker
Cole (1968) - HL 1.37-2.01 mm, HW 1.38-2.16 mm, CI 100.7-107.5, SL 1.10-1.45 mm, SI 67.1-79.7, EL 0.38-0.46 mm, EW 0.23-0.27 mm, OI 22.8-27.8, WL 1.60-2.28 mm, PNL 0.42-0.57 mm, PNW 0.30-0.53 mm, PPL 0.38-0.46 mm, PPW 0.49-0.65 mm.

Mandible as shown in Pl. III, Fig. 14; teeth short, blunt, robust; apical tooth distinctly longer than subapical; first four basal teeth subequal in length, ultimate basal tooth a little shorter and narrower than or subequal to penultimate basal and not set off from the broadly convex basal mandibular margin.

Base of antennal scape as illustrated in Pl. IV, Fig. 16; curvature of shaft rather strong, even, confined mostly to basal half; shaft rather strongly constricted and somewhat flattened along strongest part of bend. Basal enlargement considerably reduced (as compared with that of barbatus), trumpet-shaped; superior declivity long, somewhat concave, not steep; apex of superior lobe acute; superior and inferior lobes subequal in size. Lip moderately thick, curved distad, not so massive as that of barbatus or apache, not bipartite. Longitudinal peripheral carina weak or absent. Point faint or absent. Basal flange straight, thin, continuing to apex of superior lobe. Basal impression moderately developed.

Cephalic rugae longitudinal, very dense, very fine, very closely spaced, producing a silky luster; interrugal spaces subopaque or somewhat shining, finely punctate, the punctures in single rows. Posterior corners of head mostly smooth and shining, sometimes faintly striate.

Contour, in lateral view, of thorax, petiole, and post petiole as shown in Pl. V, Fig. 3; epinotum armed with a pair of well-developed, rather slender spines which are generally long, but may be short or of medium length, notably broader basally than apically, sharp. Petiolar peduncle with a strong, rather blunt, spinelike, ventral process continued posteriorly as a translucent longitudinal carina, the two bearing 3 to 5 prominent, ventrally directed hairs. Anterior declivity of peliolar node meeting the peduncle at a weak, generally well-rounded angle; dorsum of petiolar node weakly convex. Ventral process of postpetiole weak, blunt. Contour, in dorsal view, of petiolar and postpetiolar nodes as illustrated in Pl. VII, Fig. 22. Thoracic rugae less delicate and less closely spaced than of pronotum and mesonotum, transverse elsewhere; finer and more closely spaced on propleura; interrugal spaces finely punctate or reticulate, subopaque or shining. Petiolar node finely punctate and transversely, unevenly striate or rugulose; interrugal spaces somewhat shining. Postpetiolar node densely and finely punctate, faintly and irregularly striate on posterior portion, the surface slightly shining. Gaster finely shagreened, smooth, shining.

Body color varying from pale ferrugineous red with or without a darker gaster to dark ferrugineous red with posterior margin of each gastric segment strongly infuscated.

Queen
Cole (1968) - HL 1.71-2.01 mm, HW 1.94-2.13 mm. CI 113.1-120.9, SL 1.14-1.60 mm, SI 58.7-65.9, EL 0.46-0.53 mm, EW 0.30-0.38 mm. OI 26.3-26.9, WL 2.55-3.19 mm, PNL 0.38-0.53 mm, PNW 0.53-0.66 mm, PPL 0.53-0.56 rum, PPW 0.84-0.95 mm.

Conformation of base of antennal scape similar to that of worker. Cephalic rugae delicate, dense, closely spaced, not at all diverging toward posterior corners of head; interrugal spaces shining, very faintly and finely punctate; posterior corners of head smooth and shining.

Pronotum with delicate, irregularly spaced, rather dense striae; rugae on scutum dense, fine, closely spaced, longitudinal; scutellum with sparse, fine, longitudinal striae, mostly limited to lateral portions, midregion very smooth and shining; meso- and meta thoracic pleura with dense, fine, longitudinal rugulae; epinotum with rugae transverse, irregularly and somewhat more widely spaced; interrugal spaces shining, faintly and finely punctate. Epinotum armed with a pair of short, sharp spines that are much broader basally than apically. Anterior declivity of petiolar node meeting peduncle at a broad angle; apex of node blunt, the dorsum, in lateral view, broadly convex; petiolar peduncle with a prominent, angulate, longitudinally elongate, ventral process which bears 8 to 10 moderately long, straight, slender, ventrally directed hairs; dorsum of petiolar node with a few, sparse, uneven rugae with a transverse trend, the surface moderately shining, very finely punctate. Ventral process of post petiole weakly developed. Postpetiolar node rather smooth and shining, finely punctate, bearing sparse, irregular, transverse rugulae restricted to posterior portion. Gaster without perceptible sculpture at a magnification of 90X.

Color varying from a rather uniform, light to dark, ferrugineous red.

Male
Cole (1968) - HL 1.33-1.48 mm, HW 1.60-1.80 mm, CI 120.3-121.3, SL 0.65-0.66 mm, SI 36.9-40.6, EL 0.45-0.61, mm, EW 0.30-0.34 mm, OI 33.8-4l.2, WL 2.37-2.67 mm, PNL 0.49-0.57 mm, PNW 0.61-0.72 mm, PPL 0.49-0.53 mm, PPW 0.81-0.95 mm.

Mandible as shown in Pl. VIII, Fig. 13; characterized by a rather poorly defined, oblique, masticatory margin which meets the basal margin at a pronounced, even convexity; entire composite margin, from base of blade to basalmost tooth, evenly and broadly convex; distal portion of apical margin straight, proximal part distinctly concave; masticatory margin with a broad, subacute tooth and 4 irregular, poorly defined additional teeth. Cephalic rugae very fine, closely spaced, dense, becoming sparser and more widely spaced on vertex, fading out on occiput, subcrescentic above the eyes, absent from occipital corners which are smooth and shining and bear small piligerous punctures; interrugal spaces of head smooth, shining, without punctures.

Entire thorax mostly very smooth and shining; scutum with faint, sparse striae limited chiefly to posterior portion where they converge medioposteriorly; mesothoracic sternites with numerous, fine, irregular, broken, longitudinal striae; mesothoracic epimera with a few, distinct, elongate foveae. Epinotum armed with a pair of very weak tubercles. Petiole and post petiole very smooth and shining; sides of petiolar node with sparse, elongate, piligerous foveae. Gaster very smooth and shining, not shagreened. Paramere as shown in Pl. X, Fig. 13 and Pl. XI, Fig. 14.

Head and thorax deep brownish black; petiole, post petiole, and especially the gaster much lighter.