Pheidole obtusospinosa

Stefan Cover (unpublished field notes), who has collected obtusospinosa many times in southern Arizona, has found it consistently in woodland, variously composed of different combinations of pine, oak, and juniper. It typically nests under rocks, although Cover found one colony beneath a cow pat and another 2.5 m from the ground in the dead branch of a standing oak tree (Quercus arizonica). Creighton (1958) reports that colonies are much smaller than those of the closely related Pheidole hirtula, and that in southern Arizona nuptial flights occur in early July. (Wilson 2003)

Identification
This is a polymorphic species, which has the usual minors, intermediate sized workers (which look like major workers of other species) and very large major workers. The scape is flattened at the base, but the flattened area is not as wide as the width of the scape near the apex. It extends about 2/3 the length of the head in the largest workers, but may extend nearly to the posterior lateral lobes in the smallest majors. The entire dorsal surface of the head is sculptured, with granulose sculpture on the front faces of the posterior lateral lobes. The entire dorsum of the head is dull. The mesonotum projects above the level of the pronotum and propodeum. The dorsal surface of the gaster is finely punctate. (Mackay and Mackay 2002)

See the description in the nomenclature section.

Key to the Pheidole of the United States

Distribution
Known from the mountains of southern Arizona at 300–1900 m, New Mexico (very common in Clanton Draw in the Coronado National Forest, Hidalgo Co.), and from Nayarit to Nuevo Leon in Mexico. (Wilson 2003)

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

Habitat
Creosotebush scrub, grasslands, oak-pinyon-pine forests, pinyon-juniper communities, Chihuahua pine, up to 2100 m elevation. (Mackay and Mackay 2002)

Biology
This species nests under stones, often the largest stones in an area, or nests in the soil with several separate entrances. It is common in sandy soils, including dunes, but also occurs in areas of rocky loam. Brood is found in nests in March. They are preyed on by Neivamyrmex leonardi, and make no attempt to defend the nest and only escape and rescue brood. Foragers are both diurnal and nocturnal, and visit extrafloral nectaries. (Mackay and Mackay 2002)

Nomenclature

 *  obtusospinosa. Pheidole obtusospinosa Pergande, 1896: 889 (s.) MEXICO. Junior synonym of subdentata Pergande: Wheeler, W.M. 1914b: 50; hence first available replacement name for Pheidole subdentata Pergande, 1896: 888 [Junior secondary homonym of Oecophthora subdentata Mayr, 1853a: 145.]; designated by Bolton, 1995b: 326. See also: Wilson, 2003: 587.
 * subdentata. Pheidole subdentata Pergande, 1896: 888 (w.) MEXICO. [Junior secondary homonym of subdentata Mayr, above.] Subspecies of vasliti: Wheeler, W.M. 1914b: 50. Revived status as species: Creighton, 1958: 211. Senior synonym of obtusospinosa: Wheeler, W.M. 1914b: 50; of arizonica: Creighton, 1958: 211. Replacement name: obtusospinosa Pergande, 1896: 889; first available replacement name for subdentata Pergande: Bolton, 1995b: 326.
 * arizonica. Pheidole arizonica Santschi, 1911d: 3, fig. (s.) U.S.A. Subspecies of vasliti: Creighton, 1950a: 192. Junior synonym of subdentata: Creighton, 1958: 211; Gregg, 1959: 31.

Description
From Wilson (2003): DIAGNOSIS A large trimorphic species placed in the pilifera group because of the 2-toothed hypostoma of the major but with other traits conforming to the fallax group. Very close to Pheidole hirtula, distinguished most readily in the supermajor, as illustrated, by the elongate foveae of the rear half of the dorsum of the head, with the interspaces densely foveolate and opaque. The tangled taxonomic history of this species and the true status of Pheidole vaslitii, previously associated with it but now revealed as a junior synonym or sibling species of Pheidole hyatti (q.v.), have been presented by Ward (2000).

MEASUREMENTS (mm) Supermajor: HW 2.50, HL 2.36, SL 1.12, EL 0.26, PW 1.06. Major: HW 1.44, HL 1.46, SL 1.12, EL 0.24, PW 0.72. Minor: HW 0.62, HL 0.80, SL 0.98, EL 0.16, PW 0.44.

COLOR All castes: yellowish to reddish brown.



'''Figure. Upper: major, with heads of major (left) and supermajor (right). Lower: minor. ARIZONA: Sunnyside Canyon, Huachuca Mts., Cochise Co. (Stefan Cover). Scale bars = 1 mm.'''

Type Material
MEXICO. Tepic, Nayarit, col. Eisen and Vaslit, - as reported in Wilson (2003)

Etymology
L obtusospinosa, with blunt thorns, referring to the propodeal spines. (Wilson 2003)