Pheidole desertorum

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. (Wilson 2003)

Identification
See the description in the nomenclature section.

Distribution
Abundant from western Oklahoma and Texas west to southern Utah, Nevada, and California, and south into northern Mexico. (Wilson 2003)

This taxon was described from the United States.

Biology
Wheeler's (1906) account of this species included the following: "The types of this species, comprising several specimens of each of the above described phases, were taken at Fort Davis, Texas (5400 feet), during June,. 1902. It forms rather populous colonies under stones or in rough crater nests, often in very dry spots in the desert, and like Ph. dentata is highly carnivorous. I have taken it also at Ash Fork, Prescott, Phoenix, and Tucson, Arizona (May, 1905). In Prescott one of the colonies was found nesting in a dry pine log. In both soldiers and workers from this locality the epinotal spines are very short, almost absent in the worker."

Description
From Wilson (2003): Similar to Pheidole hyatti, Pheidole portalensis, Pheidole vistana; see also Pheidole ariel, Pheidole sitiens and Pheidole skwarrae, 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 profile 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.



'''Figure. Upper: lectotype, major (antennae missing; companion outline of full-face view of head shows antennal scape of major from Portal, Arizona, to illustrate scape). Lower: paralectotype, minor. Scale bars = 1 mm.'''

Type Material
- as reported in Wilson (2003)

Type Locality Information
TEXAS: Ft. Davis, Jeff Davis Co., 1650 m, col. W. M. Wheeler.

Etymology
L desertorum, of the wastelands (deserts). (Wilson 2003)

Additional References
Davidson, D. W. 1977a. Species diversity and community organization in desert seed-eating ants. Ecology 58: 711–724.

Droual, R. 1983. The organization of nest evacuation in Pheidole desertorum Wheeler and P. hyatti Emery (Hymenoptera: Formicidae). Behav. Ecol. Sociobiol. 12: 203–208.

Droual, R. and H. Topoff. 1981. The emigration behavior of two species of Pheidole (Formicidae: Myrmicinae). Psyche (Camb.) 88: 135–150.

Helms, K. R. 1995. Natural history of the ant Pheidole desertorum Wheeler in a desert grassland habitat. Psyche (Camb.) 102(1–2):35–47.

[[Media:Helms & Rissing 1990.pdf|Helms, Ken R. & Rissing, Steven W. 1990. Single Sex Alate Production by Colonies of Pheidole desertorum and Pheidole xerophila tucsonica (Hymenoptera: Formicidae). Psyche. Volume 97 (1990), Issue 3-4, Pages 213-216PDF]]

Wheeler, W. M. 1906. The ants of the Grand Cañon. Bull. Am. Mus. Nat. Hist. 22: 329–345.

Whitford, W. G. 1978. Structure and seasonal activity of Chihuahua desert ant communities. Ins. Soc. 25: 79–88.

Text and images from this publication used by permission of the author.