Pheidole megacephala

An aggressive species that can form large colonies. Introduced, and considered a pest and invasive species, in many tropical and subtropical regions.

Identification
See the description in the nomenclature section.

Distribution
New World - Widespread although spottily distributed, and sometimes locally very abundant, from southern Florida, Bermuda, and the Bahamas south through the West Indies, southern Mexico, and Central America, to as far south in South America as Santa Catarina, Brazil. (Wilson 2003)

Biology
From Wilson (2003): The colonies, which are continuous, with no evident pheromone-based boundaries, and large numbers of fertile queens, are able to reach enormous size. In some areas, especially islands such as Madeira, Culebrita, and the Dry Tortugas, they form a virtually continuous supercolony that excludes most other ant species. They do best in relatively moist, disturbed habitats, thus thrive around human habitations and in cultivated land. Nest sites are highly variable, from within and beneath rotting logs and underneath rocks and sidewalk flagstones to the bark and trunk-based detritus of standing trees. Columns of foragers travel substantial distances from one nest site to another and to food sources. P. megacephala are aggressive toward other species, and war with populations of such locally dominant species as the Indo-Australian weaver ant Oecophylla smaragdina and the cosmopolitan Argentine ant Linepithema humile (= Iridomyrmex humilis). General accounts of this important species are given by Wilson (1971), Holldobler and Wilson (1990), and D. F. Williams et al. (1994). A bibliography of the ant for North America is provided by D. R. Smith (1979). The devastating effect on the native Hawaiian insect fauna was described by the pioneering entomologist R. C. L. Perkins (1913).

While this species nests most commonly outside, when found in buildings they occupy ceilings, wall cavities, power outlets and nearly any suitable space.

Eguchi (2008) - For detailed information on biology and ecological and economic impacts of this species see Reimer et al. (1993), Campbell (1994), Hoffmann (1998), Wetterer (1998), Hoffmann et al. (1999), Vanderwoude et al. (2000), etc.

Castes
For additional images see Pheidole megacephala image gallery.

Worker
Minor

Nomenclature

 * edax. Formica edax Forskål, 1775: 84 (w.) EGYPT. Junior synonym of megacephala: Emery, 1892b: 160; Dalla Torre, 1892: 90. [If synonymy correct then edax is the senior name; however, under Art. 23.9 of ICZN (1999) edax is a nomen oblitum.]
 *  megacephala. Formica megacephala Fabricius, 1793: 361 (s.) no locality given. Latreille, 1802c: 232 (q.); Mayr, 1861: 70 (s.w.q.m.); Wheeler, G.C. & Wheeler, J. 1953b: 75 (l.). Combination in Pheidole: Roger, 1863b: 30. Senior synonym of trinodis: Roger, 1863b: 30; of edax: Dalla Torre, 1892: 90; Emery, 1892b: 160 (see note under edax); of perniciosa: Emery, 1915j: 235; of pusilla (and its junior synonyms janus, laevigata Smith, laevigata Mayr): Wheeler, W.M. 1922a: 812; of suspiciosa: Donisthorpe, 1932c: 455; of testacea: Brown, 1981: 530; of agilis: Eguchi, 2008: 56; of bernhardae, gietleni, picata, scabrior: Fischer & Fisher, 2013: 333. [P. megalocephala Schulz, 1906: 155; unjustified emendation.] Current subspecies: nominal plus costauriensis, duplex, ilgi, impressifrons, melancholica, nkomoana, rotundata, speculifrons, talpa. See also: Eguchi, 2001b: 77; Wilson, 2003: 549.
 * trinodis. Myrmica trinodis Losana, 1834: 327, pl. 36, fig. 6 (w.) ITALY. Junior synonym of megacephala: Roger, 1863b: 30.
 * pusilla. Oecophthora pusilla Heer, 1852: 15, pl. 1, figs. 1-4 (s.w.q.m.) PORTUGAL (Madeira I.). Combination in Pheidole: Smith, F. 1858b: 173. Subspecies of megacephala: Emery, 1915j: 235. Senior synonym of janus: Mayr, 1886c: 360; of laevigata Smith: Roger, 1859: 259; Emery, 1915j: 235; of laevigata Mayr: Mayr, 1870b: 981 (footnote). Junior synonym of megacephala: Wheeler, W.M. 1922a: 812.
 * agilis. Myrmica agilis Smith, F. 1857a: 71 (w.) WEST MALAYSIA. Combination in Pheidole: Donisthorpe, 1932c: 449. Junior synonym of megacephala; Eguchi, 2008: 56.
 * janus. Pheidole janus Smith, F. 1858b: 175, pl. 9, figs. 13-17 (s.w.) SRI LANKA. Junior synonym of pusilla: Mayr, 1886c: 360.
 * testacea. Atta testacea Smith, F. 1858b: 168 (s.w.) BRAZIL. Combination in Pheidole: Mayr, 1886c: 360. Junior synonym of megacephala: Brown, 1981: 530.
 * perniciosa. Oecophthora perniciosa Gerstäcker, 1859: 263 (w.) MOZAMBIQUE. [Also described as new by Gerstäcker, 1862: 516.] Combination in Pheidole: Roger, 1863b: 31. Junior synonym of megacephala: Emery, 1915j: 235.
 * suspiciosa. Myrmica suspiciosa Smith, F. 1859a: 148 (w.) INDONESIA (Aru I.). Junior synonym of megacephala: Donisthorpe, 1932c: 455.
 * scabrior. Pheidole megacephala var. scabrior Forel, 1891b: 178 (s.w.) MADAGASCAR. Junior synonym of megacephala: Fischer & Fisher, 2013: 333. See also: Forel, 1897c: 188.
 * picata. Pheidole megacephala var. picata Forel, 1891b: 178 (s.w.) MADAGASCAR. Subspecies of megacephala: Forel, 1895a: 49; of punctulata: Forel, 1897c: 186; Forel, 1905b: 163; Santschi, 1910c: 370. Raised to species: Emery, 1915j: 245; Wheeler, W.M. 1922a: 1019. Junior synonym of megacephala: Fischer & Fisher, 2013: 333.
 * gietleni. Pheidole punctulata r. gietleni Forel, 1905b: 164 (s.w.) MADAGASCAR. Subspecies of picata: Emery, 1915j: 245. Junior synonym of megacephala: Fischer & Fisher, 2013: 333.
 * bernhardae. Pheidole picata var. bernhardae Emery, 1915j: 245 (s.w.) MADAGASCAR. [First available use of Pheidole punctulata r. spinosa var. bernhardae Forel, 1905b: 164; unavailable name.] Junior synonym of megacephala: Fischer & Fisher, 2013: 333.

Myrmica agilis

Three worker minor syntypes in. Labelled “35 Malac.” (= Malacca, West Malaysia).

Myrmica suspiciosa

Two worker minor syntypes in. Labelled “Aru.”

Pheidole megacephala

Holotype worker major in. Labelled “Bac. 53.”

Description
From Wilson (2003): DIAGNOSIS Major and minor: in side view, entire postpetiole oval in shape, with all of the ventral margin bulging in a conspicuous convexity, and the node oval, low, and weakly developed; mesonotal convexity absent, the promesonotal profile forming a nearly smooth semicircle; color brownish yellow.

Major: outline of head plus mandibles in full-face view forms a near-perfect heart shape; rugoreticulum present between eye and antennal fossa.

Minor: occiput broad, lacking an occipital collar.

MEASUREMENTS (mm) Major (Grand Bahama Island): HW 1.32, HL 1.32, SL 0.64, EL 0.18, PW 0.60. Minor (Grand Bahama Island): HW 0.54, HL 0.62, SL 0.66, EL 0.12, PW 0.34.

COLOR Major and minor: brownish yellow.



'''Figure. Upper: major. Lower: minor. BAHAMAS: Grand Bahama Island. Scale bars = 1 mm.'''

Etymology
Gr L megacephala, large-headed, referring to the major. (Wilson 2003)