Pheidole rhea

This species is found on plateaus and among foothills at the base of mountains across a wide elevational range, from 1100 to 2100 m, with an apparent preference for the lower end (Creighton 1950: 168). According to Stefan Cover (personal communication), it “forms enormous colonies surmounted by sloppy craters or under rocks, chiefly on open, rocky slopes. Seeds are harvested in large quantities, but the ants are active predators as well. Mature colonies have well-developed trunk-trail systems. Minors and medias forage, but large majors and supermajors are seldom seen outside the nests. The ants are aggressive, and all size classes actively defend the nest.” (Wilson 2003)

Identification
This is a large, polymorphic species, in which the propodeal spines of both the major and minor are unusually long and sharp. The gaster is rounded anteriorly, where it connects to the postpetiole. The entire dorsum of the head is covered with striae, which diverge towards the posterior lateral lobes. These striae may form concentric whorls on the posterior lateral lobes of the largest workers. The apex of the petiole is relatively sharp, and may be bidentate in the largest workers. The lateral connules are well developed. (Mackay and Mackay 2002)

Also see the description in the nomenclature section.

Key to the Pheidole of the United States

Distribution
Southern Arizona, New Mexico and south into Mexico.

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

Habitat
Upland open and grassy slopes in mountain foothills. Nests are found on plateaus or in foothills at the bases of mountains, from 1100 - 2200 meters. (Mackay and Mackay 2002)

Biology
This species nests in the soil, and nests can be very large. They are not commonly collected in the United States, and are much more common in México. The majors have such heavy heads, that they become “stuck” in a position with the heads down and the remainder of the body and legs kicking in the air! (Mackay and Mackay 2002)

Male
Additional images can be found here.

Nomenclature

 *  rhea. Pheidole rhea Wheeler, W.M. 1908e: 452 (q.) U.S.A. Smith, M.R. 1943c: 7 (s.w.). Combination in P. (Macropheidole): Smith, M.R. 1943c: 5. Junior synonym of fimbriata: Wheeler, W.M. 1915b: 403; Emery, 1921f: 81. Revived from synonymy: Smith, M.R. 1943c: 7. See also: Gregg, 1949a: 70; Creighton, 1950a: 168; Wilson, 2003: 594.

Description
From Wilson (2003): DIAGNOSIS A giant species, reddish to dark brown, tentatively placed in the pilifera group because of the bidentate hypostoma and presence of a supermajor, but with overall appearance similar to some species of the fallax group. Trimorphic, with major, supermajor, and minor castes, as illustrated. Also distinguished as follows.

Major: head completely covered everywhere except on frontal triangle by dense longitudinal carinulae; promesonotum smoothly convex in both side and dorsal-oblique views; propodeal spines very long; posterior face of propodeum descends vertically; postpetiole diamond-shaped from above. Supermajor: propodeum descends vertically; postpetiole diamond-shaped from above; cephalic sculpturing as in major, except that the carinulae of the dorsal face behind the level of the eye curve inward toward the cephalic midline.

Minor: very long propodeal spines, as illustrated.

MEASUREMENTS (mm) All castes measured are from Stratton, Santa Catalina Mts., Arizona. Supermajor: HW 3.86, HL 4.04, SL 1.68, EL 0.38, PW 1.38. Major: HW 2.52, HL 2.76, SL 1.40, EL 0.26, PW 1.04. Minor: HW 0.86, HL 0.96, SL 1.06, EL 0.16, PW 0.58.

COLOR Major and minor: body light reddish brown, except for the gaster, which is a slightly contrasting dark reddish brown.



'''Figure. Upper: major, with partial view of supermajor head at far right. Lower: minor. ARIZONA: Stratton, Santa Catalina Mts., northeast of Tucson. Scale bars = 1 mm.'''

Type Material
Nogales, Arizona. Unique holotype queen: Department of Entomology Collection, Cornell University, Ithaca, New York. - as reported in Wilson (2003)

Etymology
NL rhea, a South American genus of ostrich-like birds, allusion unknown. (Wilson 2003)