Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Pheidolini
Genus: Pheidole
Species: P. megacephala
Binominal name: Pheidole megacephala
Synonyms: Atta testacea, Formica edax, Formica megacephala, Myrmica laevigata. Myrmica suspiciosa, Myrmica trinodis, Oecophthora perniciosa, Oecophthora pusilla, Pheidole janus, Pheidole laevigata
Common names: Big-headed ant, Coastal brown ant, Brown house-ant, Coastal brown-ant, Lon ant, African Big-headed ant. BHA

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Pheidole megacephala is a species of ant in the family Formicidae It is a very successful invasive species and is considered a serious threat to biodiversity. It is a danger through aggression to New Zealand’s native ants. It has been nominated as one of the hundred "World's Worst" invaders. The first record establishment of this species in New Zealand was in 1942 in a chocolate factory in Auckland. It had been intercepted a few years earlier and has since been intercepted at New Zealand’s ports on a regular basis. It currently appears to be restricted to coastal suburbs of Auckland, although it is likely that coastal areas north of Auckland would also be suitable. Large populations have also been reported on the Kermadec Islands 800 km north of New Zealand. Most of New Zealand is probably too cold for this species.
Pheidole megacephala is a dimorphic species having two types of worker ants, the major ant (soldier) and the minor ant (worker). The common name of bigheaded ant derives from the soldier's disproportionately large head. The soldier ants have a length of 4 mm and it has a massive, light brown head. The worker ant is smaller at 2 mm and it’s light brown head is much smaller. Minor workers are much more numerous than the soldiers. The rear half of the head of this species is smooth and glossy and the front half sculptured.
The colour of both worker types varies from yellowish-brown or reddish-brown to nearly black. All over the bodies of these ants, there are long thin hairs. This ant’s antennae are 12-segmented, usually with a 3-segmented club tip. The queen ants develop big wings.
They feed on seeds, dead insects, small invertebrates and honeydew excreted by insects. The moving of seeds by these ants facilitates the invasion of introduced plant species. This ant is known to chew on irrigation, telephone cabling and electrical wires. They are a soil-nesting ant and nest in colonies underground. The entrances typically have a mound of extracted soil at their entrances. They will excavate disturbed soils, lawns, flowerbeds, under objects, such as bricks, cement slabs, or flower pots, around trees or water pipes, the base of structures, driveways and walkways. They do invade homes.
This species reproductive success is due to the nest being multi-queened and they are able to spread by budding off groups of workers along with inseminated queens. Overseas by budding they have formed interconnected super-colonies that cover tens of hectares.
Nuptial flights of winged ants take place during the winter and spring and afterwards the fertilised queens shed their wings after finding suitable nesting sites to start new colonies. 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.

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Multiple queens in a colony of Pheidole megacephala big-headed ants.1-Pheidole megacephala Queens.jpg

The photo below is of another Big Headed ant species (Pheidole pilifera) showing the difference in size between that of a minor worker (left) compared with a major worker (right). 
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Video of a colony

Thanks to Wikipedia for text and information: