Pheidole megacephala

Nomenclature

Species: Pheidole megacephala (Fabricius, 1793)

Usage: valid
Vernacular name: Big Headed Ant

Paratype: CASC - BLF12003 - CASENT0056016
Syntype: OUMNH - ANTC20932 - CASENT0901409
Syntype: OUMNH - ANTC20933 - CASENT0901410

General description

Pheidole megacephala is a common tramp species with two waist segments, 12-segmented antennae, 3-segmented antennal clubs,propodeal spines, long thin pilosity, and a bimorphic worker caste. The minor workers are small, yellow to brown, small propodeal spines, and no antennal scrobes. Sculpture on the minor worker is restricted to the middle and posterior portions of the mesosoma. The major workers are larger and have oversized, mostly unsculptured heads without antennal scrobes. Pheidole megacephala is known to cause significant damage to native biological diversity, including vertebrates, and also significant damage to agricultural systems. The species is considered to be one of the worst 100 invasive species in the world according to the IUCN/SSC Invasive Species Specialist Group (ISSG). Pheidole megacephala recruits strongly to baits and food resources and forms long and busy foraging trails. Minor workers are much more abundant than major workers, both outside of and within the nest.

External links

Antweb | Antwiki

Diagnostic description

Diagnosis of worker among Antkey species

Worker castes bimorphic. Head shape ovoid (minor workers) or weakly heart-shaped with posterolateral lobes (majors), but never triangular. Antenna 12-segmented. Antennal club 3-segmented. Antennal insertions at least partly covered by frontal lobes; not surrounded by a raised sharp-edged ridge. Frontal lobes do not obscure face outline between mandible and eye; relatively close together so that the posteromedian portion of the clypeus, where it projects between the frontal lobes, is at most only slightly broader than one of the lobes. Posterolateral corners of head unarmed, without spines. Mandibles triangular. Mesosoma with erect hairs. Pronotal spines absent. Propodeum armed with spines or teeth. Slope of mesosoma steep. Waist 2-segmented. Petiole pedunculate with a distinct and upright node; lacking large subpetiolar process. Postpetiole attached to lower surface of gaster. Color yellowish brown to brown. Minor worker characters. Head smooth and shining, lacking punctation. Antennal scrobe lacking. Postpetiole swollen relative to petiole. Major worker characters. Antennal scrobe weak to absent; no depression capable of receiving antennal scapes clearly visible. Posterolateral lobes smooth and shining, lacking rugae and punctation.

Minor workers of P. megacephala are most easily distinguished from P. anastasii, P. bilimeki, P. flavens, P. moerens and P. punctatissima by the smooth and shining head. They are most easily separated from the remaining Antkey Pheidole minors by the postpetiole, which is distinctly swollen in comparison to the petiole. The major workers are separated from all other Antkey Pheidole majors in the United States by the heart-shaped head and by the smooth and shining posterolateral lobes that lack both rugae and punctation.

Distribution

Click here for updated occurrence data and map on antmaps.org
Click here for updated occurrence data and map on GBIF.org

Videos of live ants

Pheidole megacephala, Hawaii , 03-29-2011

Pheidole megacephala nesting in soil, Hawaii, 04-02-2011

Pheidole megacephala, foraging trail, Hawaii, 04-02-2011

Pheidole megacephala nesting in soil, Hawaii, 03-29-2011

Pheidole megacephala major worker, Hawaii, 03-29-2011

<em>Pheidole megacephala</em> at peanut butter bait

Pheidole megacephala at peanut butter bait (Suva, Fiji). Only minor workers are shown in this video, although P. megacephala also has larger major workers.

A major worker of the big-headed ant. Photo by ©Alexander L. Wild, alexanderwild.com	Minor workers of the big-headed ant tend aphids for honeydew. Photo by ©Alexander L. Wild, alexanderwild.com
Photo by ©Alexander L. Wild, alexanderwild.com	Adults inside the brood nest of a big-headed ant colony. Photo by ©Alexander L. Wild, alexanderwild.com
Anterior view of head, adult worker. Posterolateral lobes.	Anterior view of head, adult worker. Posterior third of cephalic dorsum lacking sculpture.
Anterior view of head, adult worker. The head of the soldier is somewhat heart-shaped with the evenly rounded posterolateral lobes bulging laterally and the head attenuating anteriorly. Used in Antkey to separate majors of Pheidole megacephala from other majors of other Pheidole.	Anterior view of antennal scrobe, adult worker. Antennal scrobe very weak, not capable of accommodating entire scape.
Anterior view of antennal scape, adult worker. Antennal scapes.	Anterior view of head, adult worker. The posterior third of cephalic dorsum smooth and shining with at most a few short interrupted carinae. Used in Antkey to separate major workers of Pheidole megacephala from those of other Pheidole species.
Anterior view of antennal scape, adult worker.	Lateral view of waist, adult worker. The postpetiole of the major and minor worker is distinctly larger in volume than the petiole. Used in Antkey to separate Pheidole megacephala from other species of Pheidole.
Lateral view of postpetiole, adult worker. Postpetiole swollen relative to petiole.