Pogonomyrmex texanus

This ant nests in the soil, with the entrance hole surrounded by a small (10 - 15 cm diameter) mound. It occurs in rocky areas within the Chihuahuan Desert (Mackay & Mackay, 2002).

Identification
Workers of this species can be recognized as being large ants (total length greater than 9 mm), which lack propodeal spines. The anterior border of the clypeus is concave, but not to the extent of the clypeus of Pogonomyrmex apache. The rugae on the dorsum of the head are fine, nearly parallel, directed straight back to the posterior margin, the posterior lateral corner is smooth and shining.

It can be separated from most of the species in the genus by the lack of propodeal spines. It is much larger than Pogonomyrmex californicus and most workers of Pogonomyrmex maricopa. It can also be separated from these two species, in which the anterior border of the clypeus is nearly straight. (Mackay & Mackay, 2002.)

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

Habitat
Rocky areas within the Chihuahuan Desert.

Biology
Francke and Merickel (1982) - We have collected and studied 21 nest series of P. texanus. All the nests were found in open situations, mostly in level terrain (16 of 21; greatest slope exposure noted 20°). The altitudinal range is 580-1645 m (1900-5400 ft), with most (n = 15) coming from 610-915 m (2000-3000 ft). Soil characterization of the nests is as follows: clay 8, sandy clay loam 4, clay loam 3, silty clay loam, sandy, and sandy clay 1 each. Conical craters with a central depression, ranging from 5 cm diameter and 2.5 cm high to 25 cm x 10 cm (predominantly about 10 cm x 6 cm), were present on 16 nests; relatively flat discs were present on two (30 cm and 12 cm diameter, respectively); and on three occasions no excavated material about the nest entrance was observed.

The workers move slowly and at a steady gait, in contrast to the erratic, hesitant gait of Pogonomyrmex apache (see Cole, 1954, 1968; pers. obs.). The gaster is usually held parallel to the substrate, in contrast to P. desertorum which frequently forages with the gaster turned downward (Cole, 1968; pers. obs.). Colonies are usually small (less than 100 workers), and there is no aggressive response when the nest is disturbed.

To crudely determine the relative potency of the venom of P. texanus, the senior author allowed one worker to sting him on the forearm. The symptoms experienced are very similar to those resulting from envenomation by Pogonomyrmex barbatus or Pogonomyrmex rugosus.

Nomenclature

 *  texanus. Pogonomyrmex (Pogonomyrmex) texanus Francke & Merickel, 1982: 375, figs. 4, 7, 8, 11, 13, 14, 16 (w.m.) U.S.A. Taber, 1988: 244 (q.).

Worker
Measurements of holotype followed, in parenthesis, by the ranges observed in paratypes: Head length 2.15 mm (2.05-2.35 mm), head width 2.45 mm (2.15-2.56 mm), cephalic index 113.95 (104.88-113.95), scape length 1.65 mm (1.45-1.75 mm), scape index 74.08 (74.08-75.49), maximum eye length 0.45 mm (0.40-0.48 mm), maximum eye width 0.35 mm (0.32-0.38 mm), ocular index 20.93 (19.51-20.93), Weber's length 2.65 mm (2.30-2.75 mm), petiolar node length 0.75 mm (0.65-0.80 mm), maximum width of petiolar node 0.60 mm (0.49-0.60 mm), postpetiolar length 0.65 mm (0.60-0.68 mm), postpetiole width 0.80 mm (0.65-0.80 mm).

Head broader than long; eye small and weakly convex, not extending beyond lateral margin of head. Mandible with seven subequal, blunt teeth. Apical margin of mandible broadly convex, basal margin straight. Base of antennal scape similar to P. apache Wheeler: with superior lobe considerably stronger than inferior lobe; basal flange very weak on superior lobe, developed as a strongly recurved lip on inferior lobe; longitudinal peripheral carina very strong, point absent. Lateral lobes of c1ypeus produced in front of antennal insertions, margin of c1ypeal lobe broadly and shallowly excised; frontal triangle deeply impressed. Median cephalic rugae longitudinal, parallel; extremely fine and closely set, producing a silky luster; interrugal spaces shiny; in lateral view rugae not forming whorls behind eye; posterior corner of head without rugae, smooth, strongly shiny.

Contour of thorax, petiole, and postpetiole, in lateral view. Thoracic rugae dense, fine, and shiny; transverse throughout. Epinotum unarmed; posterior epinotal declivity short, smooth. Dorsal portions of metasternal flanges fused, forming a single arcuate carina across posterior declivity of epinotum. Venter of petiolar peduncle with a few long, erect hairs in vicinity of peduncular process. Petiolar node flattened dorsally; with faint, transverse striae. Postpetiolar node dorsally with faint, transverse striae. Contour of petiolar and postpetiolar nodes, in dorsal view. First gastric segment broader than long. Body color uniformly reddish brown.

Male
The two known males are of similar size, the measurements for one of them are as follows: Head length 1.62 mm, head width 1.95 mm, cephalic index 120.00, scape length 0.75 mm, scape index 42.31, maximum eye length 0.54 mm, maximum eye width 0.36 mm, ocular index 33.84, Weber's length 2.70 mm, petiolar node length 0.70 mm, maximum width of petiolar node 0.75, postpetiolar length 0.70 mm, postpetiole width 0.82 mm.

Head with lateral outline between eye and occipital corner evenly, rather strongly convex; eye not strongly convex, not strongly protruding from lateral margin of head. Basal margin of mandible strongly concave, apical margin broadly convex; both margins subparallel to each other; with four teeth, broad, blunt and robust. Antennal scape with outer surface of base evenly convex; antennal scape longer than combined lengths of first two segments of flagellum, shorter than combined lengths of first three segments of flagellum; apical segment of flagellum less than twice length of subapical segment, which is distinctly longer than wide. Anterior margin of median clypeal lobe broadly, very shallowly excised. Upper surface of head unstriated, smooth and shiny. Interocellar area with very faint longitudinal, parallel striae. Posterior corner of head smooth, shiny. Clypeus vestigially striate. Mandibles feebly rugose, shiny. Entire head with moderately dense, long, white, very fine erect hairs.

Contour of thorax, petiole, and postpetiole, in lateral view. Epinotum unarmed. Entire thorax shiny; scutum, scutellum, and basal face of epinotum very shiny. Nota smooth; pleura vestigially striate to smooth, shiny. Forewing with one cubital cell. Petiolar and postpetiolar nodes, in dorsal view; smooth and shiny throughout. Venter of petiolar peduncle with poorly developed, blunt tooth, bearing numerous erect hairs. Head and thorax black, gaster reddish brown; body hairs fine and silky, mostly pure white.

Type Material
Type nest series (workers, males, brood) from Lubbock (Farm Road 2641 at Blackwater Draw, 990 m), Lubbock Co., Texas, 2 July 1973 (J. V. Moody). Holotype worker and paratype male deposited at the California Academy of Sciences, San Francisco.

In addition to the type nest series we have examined workers (designated paratypes) from the following localities in Texas: Brewster Co., 29.2 km NE Marathon (1265 m), 27 July 1978 (T. B. Hall, J. V. Moody, O. F. Francke); 6.5 km W Marathon (1250 m), 27 July 1978 (T. B. Hall, J. V. Moody, O. F. Francke: two nest series). Coke Co., 22.7 km NW Robert Lee (610 m), 25 July 1978 (T. B. Hall, J. V. Moody, O. F. Francke). Crane Co., 8.1 km W Crane (750 m), 5 June 1979 (J. V. Moody, O. F. Francke, F. W. Merickel). Crosby Co., 17.6 km N Crosbyton (880 m), 15 June 1978 (D. P. Bartell, R. Beckham, G. Henderson, K. Neece). Culberson Co., Guadalupe Mountains National Park, mouth of McKittrick Canyon (l540m), 14 June 1978(J. V. Moody,O. F. Francke). Dickens Co., 21.9 km N Dickens (790 m), 11 June 1979 (W. D. Sissom, J. V. Moody, O. F. Francke). Hall Co., 24 km S Estelline (580 m), 8 June 1978 (D. P. Bartell, R. Beckham, G. Henderson, K. Neece). Midland Co., 48.6 km SW Midland (880 m), 5 June 1979 (J. V. Moody, O. F. Francke, F. W. Merickel: two nest series); 27.5 km S Midland (820 m), 12 August 1979 (J. V. Moody, O. F. Francke. F. W. Merickel). Pecos Co., 6.5 km SE Sheffield (670 m), 10 August 1978 (T. B. Hall, J. V. Moody, W. D. Sissom, O. F. Francke). Presidio Co., 34.7 km SW Marfa (1645 m), 8 August 1979 (J. V. Moody, O.F. Francke, F. W. Merickel). Reagan Co., 21 km W Big Lake (850 m), 10 August 1978 (T. B. Hall, J. V. Moody, W. D. Sissom, O. F. Francke: two nest series). Terrell Co., 53 km N Dryden (655 m), 21 October 1978 (E. L. Meeks, J. V. Moody). Upton Co., 11 km N Rankin (670 m), 11 August 1978 (T. B. Hall, J. V. Moody, W. D. Sissom, O. F. Francke: two nest series); 37.3 km NW Rankin (870 m), 5 June 1979 (J. V. Moody, O. F. Francke, F. W. Merickel). Paratypes deposited in the following collections: California Academy of Sciences, American Museum of Natural History, Museum of Comparative Zoology, Los Angeles County Museum, and Texas Tech University.