Pheidole desertorum Wheeler

Wilson, E. O., 2003, Pheidole in the New World. A dominant, hyperdiverse ant genus., Cambridge, MA: Harvard University Press : 284

Pheidole desertorum Wheeler

Pheidole desertorum Wheeler 1906i: 337. Syn.: Pheidole desertorum var. comanche Wheeler 1906i: 339, synonymy by Creighton 1950a:178; Pheidole desertorum var. maricopa Wheeler 1906i: 339, synonymy by Creighton 1950a: 178.

types Mus. Comp. Zool. Harvard.

etymology L desertorum , of the wastelands (deserts).

diagnosis Similar to the species listed in the heading above, distinguished from these and other members of the fallax group as follows.

Major: slender; yellow; antennal scapes very long, slightly exceeding the occipital corner; humerus subangular in dorsal-oblique view; propodeal spines short and slender in side view; a loose rugoreticulum extends from the lateral margins of each frontal lobe to the eye; central half of the dorsum of the head, mesopleuron, propodeum, and waist foveolate and opaque; the rest of the body smooth and shiny.

Minor: slender; yellow; antennal scape very long, exceeding the occipital corner by almost half its length; occiput greatly narrowed, its profde concave in full-face view, but lacking nuchal collar.

Measurements (mm) Lectotype major: HW 1.36, HL 1.42, SL (scape missing), EL 0.28, PW 0.64 (Portal, Arizona, major, HW 1.36, SL 1.32).

Paralectotype minor: HW 0.58, HL 0.82, SL 1.10, EL 0.22, PW 0.40. Color Major: reddish yellow except for gaster, which is yellowish brown. Minor: concolorous reddish yellow.

Range Abundant from western Oklahoma and Texas west to southern Utah, Nevada, and California, and south into northern Mexico.

Biology P. desertorum occurs to at least 1700 m in a wide range of desert habitats, including mesquite or acacia-dominated bajadas, rocky slopes, and desert grasslands. The colonies construct large crater nests with single entrance holes. Helms (1995) reports that colonies in southeastern Arizona are large, at maturity comprising 2,500-25,000 workers and one to multiple queens, and often occur in multiple nests. Foragers, mostly minors but with a few majors also present, are active outside the nest at night and following rains. On diet, Stefan Cover (personal communication) has stated from extensive personal experience, "Contrary to previous reports in the literature (Davidson 1977a, b; Whitford 1978), P. desertorum is an aggressive predator and scavenger, not a granivore. Seeds are only rarely collected, and then in small quantities." Most colonies produce reproductives each year, which are extremely sex-biased from colony to colony. Winged reproductives have been found in nests from early June to late August. According to Helms, mating flights occur prior to sunrise in the late summer, following rainfall. Males form aerial swarms into which the winged queens fly; mating then occurs on the ground, after which the queens fly away in search of nest sites. Colonies are usually founded by single queens, but occasionally by small groups. Droual (1983) has described the remarkably efficient maneuvers of nest defense and evacuation by desertorum colonies under attack by army ants ( Neivamyrmex nigrescens ). Droual and Topoff (1981) have demonstrated that emigrations to new nest sites also occur at a high frequency even under apparently stable environmental conditions.

Figure Upper: lectotype, major (antennae missing; companion outline of full-face view of head shows antennal scape ofmajor from Portal, Arizona, to illustrate scape). Lower: paralectotype, minor. TEXAS: Ft. Davis, Jeff Davis Co., 1650 m (W. M. Wheeler). Scale bars = 1 mm.