Pogonomyrmex rugosus

This species forms large crater-like mounds similar to those of Pogonomyrmex barbatus. Rarely it forms a small mound a few cm higher than the surface of the ground. Nests are large, containing several thousand workers. Workers are individual or group foragers, depending on the conditions. Food sources are primarily seeds (especially those of Erodium cicutarium), but also includes dead insects. The soil surface temperature limits foraging activity. The myrmecophilous scarabaeid beetle genus Cremastocheilus occurs in the nests. These ants deposit seed hulls and other debris around the edge of the mound, where it is eaten by tenebrionid beetles of the Genus Eleodes. The black widow spider is one of the main predators of this species. (Mackay and Mackay 2002)

Identification
Its color (and large size, over 8-mm total length) usually separates it from all others in the genus: dark brown, almost black head and mesosoma with a somewhat lighter colored gaster. (Mackay and Mackay 2002)

Distribution
United States: southern California, Nevada, New Mexico, southwestern (Washington Co.) and east central (Grant Co.) Utah, southwestern, southeastern and east central Colorado, western part of Oklahoma panhandle (Cimarron Co.), Texas (western part of panhandle, Big Bend region, and along the Rio Grande to Hildago Co.). Mexico: Tamaulipas, Nueva Leon, Coachuila, Zacatecas, Aguacalientes, Nayarit, Durango, Sinaloa, Chihuahua, Sonora, Baja California.

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

Habitat
Found primarily in Chihuahuan Desert communities, including grasslands, creosotebush scrub and riparian habitats. (Mackay and Mackay 2002)

Genetics
The genome of P. rugosus was sequenced for a study examining how parasitic ants with no worker caste may have altered their genome to arrive at a workerless state. In comparison to ants with a full complement of castes, there appeared to be no loss of genes in the parasitic ants. This suggests regulatory differences and not sequence differences predominate in gains and losses of castes (phenotypes). (Smith et al. 2015)

Other Ants
A host species for the workerless social parasites and.

Nomenclature

 * fuscatus. Pogonomyrmex barbatus var. fuscatus Emery, 1895c: 309 (w.q.) U.S.A. Subspecies of barbatus and senior synonym of curvispinosus, marfensis: Creighton, 1950a: 119. Junior synonym of barbatus: Cole, 1954b: 117; of rugosus: Cole, 1968: 70.
 *  rugosus. Pogonomyrmex barbatus subsp. rugosus Emery, 1895c: 309 (w.m.) U.S.A. Cole, 1968: 72 (q.); Taber, Cokendolpher & Francke, 1988: 51 (k.). Raised to species: Cole, 1968: 70. Senior synonym of similis: Creighton, 1950a: 120; of fuscatus (and its junior synonyms curvispinosus, marfensis), spadix: Cole, 1968: 70.
 * marfensis. Pogonomyrmex barbatus var. marfensis Wheeler, W.M. 1902a: 98 (diagnosis in key) (w.) U.S.A. Junior synonym of fuscatus: Creighton, 1950a: 119.
 * similis. Pogonomyrmex similis Olsen, 1934: 512, pl. 6, fig. 2 (w.) U.S.A. Junior synonym of rugosus: Creighton, 1950a: 120.
 * curvispinosus. Pogonomyrmex barbatus subsp. curvispinosus Cole, 1936b: 120 (w.) U.S.A. Junior synonym of fuscatus: Creighton, 1950a: 119.
 * spadix. Pogonomyrmex barbatus subsp. spadix Cook, 1953: 98, figs. (w.) U.S.A. Junior synonym of rugosus: Cole, 1968: 70.

Worker
Cole (1968) - HL 1.67-2.47 mm, HW 1.75-2.70 mm, CI 93.8-115.2, SL 1.18-1.67 mm, SI 60.5-71.9, EL 0.34-0.65 mm, EW 0.19-0.42, OI 17.8-28.5, WL 1.75-2.96 mm, PNL 0.34-0.72 mm, PNW 0.38-0.68 mm, PPL 0.38-0.67 mm, PPW 0.53-0.87 mm.

Mandible similar to that of Pogonomyrmex barbatus; subapical and first basal teeth subequal in length; ultimate basal tooth much longer than penultimate, strongly offset from the straight basal margin.

Base of antennal scape as shown in Pl. IV, Fig. 1 5 not discernibly different from that of barbatus. Thoracic, petiolar, and postpetiolar contours in lateral view as illustrated in Pl. V, Fig. 7; pronotum generally less evenly convex than that of barbatus, its dorsum usually flattened; epinotal armature as in barbatus.

Cephalic rugae coarse, wavy, widely and rather unevenly spaced; interrugular spaces shining to subopaque, with broken rugules, granulations, and often also with prominent punctures. Thoracic rugae coarse, especially on the pronotum where they are very strong, uneven, and form very coarse reticulations with deep, flattened interrugal spaces. Rugae on petiolar and postpetiolar nodes strong, uneven, forming definite reticulations.

Body color varying from a rather uniform, very deep brownish black or brownish red to various combinations of brown, brownish red, dark red, yellowish red, and brownish black.

Queen
Cole (1968) - HL 2.05-2.20 mm, HW 2.43-2.66 mm, CI 117.3-121.9, SL 1.52-1.63 mm, SI 60.2-63.2, EL 0.57-0.61 mm, EW 0.38-0.16 mm, OI 27.7-28.6, WL 3.53-3.80 mm, PNL 0.57-0.68 mm, PNW 0.68-0.80 mm, PPL 0.53-0.61 mm, PPW 1.10-1.18 mm.

Similar to the female of Pogonomyrmex barbatus, except cephalic and scutal rugae much coarser and notably more widely spaced, dorsum of the petiolar node prominently rugo-reticulose, body color generally black, reddish black, or deep reddish brown, with the gaster often in part or entirely much paler.

Male
Cole (1968) - HL 1.33-1.69 mm, HW 1.64-1.92 mm, CI 113.5-123.4, SL 0.55-0.68 mm, SI 32.1-35.4, EL 0.52-0.60 mm, EW 0.34-0.42 mm, OI 35.3-39.1, WL 2.34-2.94 mm, PNL 0.39-0.44 mm, PNW 0.62-0.78 mm, PPL 0.17-0.57 mm, PPW 0.70-0.91 mm.

Similar to the male of barbatus, but inner dorsal margin of paramere (Pl. X, Fig. 11) without a deep emargination, the terminal lobe not set off strongly from the base; terminal parameral lobe as shown in Pl. XI, Fig. 12. Body color generally a fuscus yellow or brown, somelimes nearly black.