|Senior synonym of Pheidole trinodis: Roger, 1863b PDF: 30; of Pheidole edax: Dalla Torre, 1892: 90; Emery, 1892c PDF: 160 (see note under Pheidole edax); of Pheidole perniciosa: Formicidae). Revue Zoologique Africaine (Brussels) 4:223-250. [1915-12-15]">Emery, 1915i PDF: 235; of Pheidole pusilla (and its junior synonyms Pheidole janus, Pheidole laevigata Smith, Pheidole laevigata Mayr): Wheeler, 1922: 812; of Pheidole suspiciosa: Donisthorpe, 1932c PDF: 455; of Pheidole testacea: Brown, 1981: 530; of Pheidole agilis: Eguchi, 2008 PDF: 56.|
|Current subspecies: nominal plus Pheidole megacephala costauriensis, Pheidole megacephala duplex, Pheidole megacephala ilgi, Pheidole megacephala impressifrons, Pheidole megacephala melancholica, Pheidole megacephala nkomoana, Pheidole megacephala rotundata, Pheidole megacephala scabrior, Pheidole megacephala speculifrons, Pheidole megacephala talpa.|
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.
Formica megacephala Fabricius , 1793: 36. Roger 1863b: 30 (combination in Pheidole ). Syntype(s): major, no locality given, not examined.
Myrmica trinodis Losana , 1834: 327. Roger 1863b: 30 (junior synonym of megacephala ). Syntype(s): "worker", Italy, not examined.
Formica edax Forskal , 1775: 84. Emery 1892: 160 (junior synonym of megacephala ), Dalla Torre 1892: 90 (same). Syntype(s): "worker", Egypt, not examined.
Oecophthora perniciosa Gerstacker , 1859: 263. Roger 1863b: 31 (combination in Pheidole ), Emery, 1915c: 235 (junior synonym of megacephala ). Syntype(s): "worker", Mozambique, not examined.
Oecophthora pusilla Heer , 1852: 15. F. Smith 1858: 173 (combination in Pheidole ), Roger 1859: 259 (senior synonym of laevigata Fr. Smith , 1855: 130), Mayr 1870: 981 (senior synonym of laevigata Mayr , 1862: 747), Mayr 1886: 360 (senior synonym of janus ), Emery 1915: 235 (subspecies of megacephala ), Wheeler 1922: 812 (junior synonym of megacephala ). Syntypes: major, minor, queen & male, Madeira, not examined.
Myrmica suspiciosa F. Smith , 1859: 148. Donisthorpe 1932: 455 (junior synonym of megacephala ). Syntype (s): "worker", Aru I. (Indonesia), not examined.
Subspecies enumerated in Bolton, 1995: nominal plus costauriensis Santschi , 1914: 443, syntype(s): major, Ghana, not examined; duplex Santschi , 1937a: 220, syntypes: major, minor & queen, Angola, not examined; ilgi Forel , 1907: 82, syntypes: major & minor, Ethiopia, not examined.; impressifrons Wasmann , 1905: 110 (replacement name for impressiceps Wasmann , 1904: 72), syntypes: major, minor & queen, South Africa, not examined; melancholica Santschi , 1912: 164, syntypes: major & minor, Ivory Coast, not examined; nkomoana Forel , 1916: 415, syntypes: major, minor, queen & male, Zaire, not examined; rotundata Forel , 1894: 92, syntypes: major & minor, Mozambique, not examined; scabrior Forel , 1891: 178, syntypes: major & minor, Madagascar, not examined; speculifrons Stitz , 1911: 386, syntypes: major & minor, Tanzania, not examined; talpa Gerstacker , 1871: 356, syntypes: "worker" & queen, Kenya, not examined. For these forms type material not examined.
Other material examined: S. China: Hong Kong: Victoria Park, Hong Kong I. [K. Eguchi]; Macau: Mong Ha [K. Eguchi]. N. Vietnam: Ha Noi: Hanoi Agric. Univ. (Gia Lam) [K. Ogata: 15-min TUS #2]; Quang Ninh: Hoanh Bo [K. Eguchi]. S. Vietnam: Vinh Long (misspelled as "Vinlong"): Vinh Long (10°15'N, 105°58'N) [S. Kawaguchi]. Thailand: Trang: Khao Chong Waterfall [Eg01-VN-761]. W. Malaysia: Penang: beside a building of Univ. Sains Malaysia [C.Y. Lee]. E. Malaysia: Sabah: Kota Kinabalu [Eg97-BOR-376], Tambunan Village [H. Okido], Danam Valley [Eg96-BOR-108]. Indonesia: Kalimantan Timur: Tandjung Isuy [Seyfert & Graindl]; Irian Jaya: Wamena, 1600 m alt. [Eg98-IRI-674, -675, -676, -703]. Australia: Queensland: S. Mission Beach near Tully [AU01-SKY-12]. Tonga: Tongatapu: Vaini [J.K. Wetterer].
Worker measurements & indices: Major (n=5). - HL 1.28-1.45 mm; HW 1.25-1.45 mm; CI 98-100; SL 0.71-0.76 mm; SI 52-57; FL 0.94-0.98 mm; FI 68-77.
Minor (n=5). - HL 0.62-0.72 mm; HW 0.55-0.65 mm; CI 88-91; SL 0.67-0.73 mm; SI 111-121; FL 0.68-0.77 mm; FI 118-123. Worker description
Major. - Head in lateral view roundly convex dorsally, not impressed on vertex, in full-face view shallowly concave posteriorly; frons longitudinally rugose (or rarely almost smooth, only sparsely with short interrupted longitudinal rugulae); vertex and dorsum of vertexal lobe smooth and shining or shagreened; frontal carina absent or present just as weak rugula(e); antennal scrobe absent; median longitudinal carina of clypeus weak or absent; hypostoma at most with a pair of very small or inconspicuous submedian processes in addition to a pair of conspicuous lateral processes; antenna with a 3-segmented club; maximal diameter of eye almost as long as or longer than antennal segment X. Promesonotal dome in dorsal view smooth and shining or shagreened, sometimes with several weak transverse rugulae, in lateral view at most with an inconspicuous mound on its posterior slope; humerus not or weakly produced laterad; the dome at the humeri narrower than at the bottom; mesopleuron, metapleuron and lateral face of propodeum weakly or very weakly punctured. Petiole a little longer than postpetiole (excluding helcium); postpetiole not massive; its anteroventral part weakly swollen. First gastral tergite smooth and shining entirely, or very weakly punctured around its articulation with postpetiole and smooth or shagreened in the remainder.
Minor. - Head smooth and shining; preoccipital carina weak but present dorsally and laterally; median part of clypeus smooth and shining, without a median longitudinal carina; antenna with a 3-segmented club; scape extending beyond posterolateral margin of head by the double length of antennal segment II or more; maximal diameter of eye almost as long as, or sometimes a little shorter than antennal segment X. Promesonotal dome smooth and shining, in lateral view lacking a mound on its posterior slope; humerus in dorso-oblique view not or hardly produced; mesopleuron, metapleuron and lateral face of propodeum punctured weakly; metanotal groove inconspicuous. Petiole almost as long as or a little longer than postpetiole (excluding helcium); postpetiole relatively long but not massive; its anteroventral part weakly swollen.
Recognition: The syntype minors of " Myrmica agilis " agree well with minors of Bornean populations (e.g., Eg96-BOR-108) of P megacephala . I conclude that P agilis is a juninor synonym of P megacephala .
P. megacephala is well distinguished from Indo-Chinese species by the combination of the following characteristics: in the major head in full-face view only shallowly concave posteriorly; in the major dorsum of vertexal lobe smooth and shining or shagreened; in the major hypostoma in the middle at most with a pair of very small or inconspicuous submedian processes; in the minor preoccipital carina weak but present dorsally and laterally; posterior slope of promesonotal dome at most with an inconspicuous mound in the major, and without any mound in the minor; in the major and minor anteroventral part of postpetiole weakly swollen.
Distribution & bionomics: Widely distributed in the world tropics and subtropics. 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.
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.
Molecular Biology and Genetics
Barcode data: Pheidole megacephala
There are 48 barcode sequences available from BOLD and GenBank. Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Pheidole megacephala
Public Records: 48
Specimens with Barcodes: 202
Species With Barcodes: 1
Pheidole megacephala is a species of ant in the family Formicidae. It is commonly known as the bigheaded ant in the USA and the coastal brown ant in Australia. It is a very successful invasive species and is considered a danger to native ants in Australia  and other places. It has been nominated as one of the hundred "World's Worst" invaders.
Pheidole megacephala was described from a specimen from the island of Mauritius by the entomologist, Johan Christian Fabricius in 1793, although a previous record exists for Egypt 18 years earlier (see Synonyms). Regardless of its original distribution, bigheaded ants have since spread to many tropical and subtropical parts of the world.
There are two types of worker ant, the major or soldier ant and the minor worker. The common name of bigheaded ant derives from the soldier's disproportionately large head. This has large mandibles which may be used to crush seeds. The soldiers are about four millimetres in length, twice as long as the minor workers. The colour of both types varies from yellowish-brown or reddish-brown to nearly black. The rear half of the head is smooth and glossy and the front half sculptured. The twelve-segmented antennae are curved and have club-like tips. The waist or petiole is two-segmented with the node immediately behind conspicuously swollen. There are a pair of short, upward-facing spines on the waist. The body has sparse, long hairs.
Bigheaded ants nest in colonies underground. Colonies can have several queens  and super-colonies can be formed by budding, when a queen and workers leave the original nest and set up a new colony nearby without swarming. In Florida, nuptial flights of winged ants take place during the winter and spring and afterwards, fertilized queens shed their wings and find a suitable site to found a new colony where they start laying eggs. Each queen lays up to 290 eggs per month. The eggs hatch after two to four weeks and the legless white larvae, which are fed by the workers, pupate about a month later. The adult workers emerge ten to twenty days after that.
The bigheaded ants feed on dead insects, small invertebrates and honeydew excreted by insects such as aphids, soft scale insects, mealybugs, whiteflies and planthoppers. These sap-sucking bugs thrive in the presence of bigheaded ants, being more abundant on plants patrolled by ants than on those not so patrolled. Green scale, Coccus viridis, flourished when bigheaded ants protected their food source by removing predators such as lady beetle larvae and lepidopteran larvae. The minor workers are much more numerous than the soldiers. Trails of ants lead up trunks, along branches and into the canopies of trees and debris-covered foraging tunnels with numerous entrances are created on the surface of the ground. These may be confused with similar tubes built by subterranean termites. Foraging ants will alert others to new food sources. Honeydew is ingested but other foodstuffs are carried back to the nest by both major and minor workers who may transfer items of food between themselves. Anything too big to be moved may be dissected before being brought back to the nest.
P. megacephala can also live indoors.
- Global Invasive Species Database
- An invasion revisited: the African big-headed ant (Pheidole megacephala) in northern Australia
- Featured Creatures
- Wilson EO. 2003. Pheidole in the New World, a Dominant, Hyperdiverse Ant Genus. Harvard University Press. Cambridge, MA. 794 pp.
- The Pest Ants of Florida
- Hoffman B. 2006. Pheidole megacephala (insect). CSIRO Sustainable Ecosystems
- Impact of Pheidole megacephala (F.) (Hymenoptera: Formicidae) on the Biological Control of Dysmicoccus brevipes (Cockerell) (Homoptera: Pseudococcidae)
- Direct and indirect interactions between ants (Pheidole megacephala), scales (Coccus viridis) and plants (Pluchea indica)