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Pheidole megacephala (Family Formicidae)

Big-headed Ant, Coastal Brown Ant, Brown House Ant, Lion Ant

Distribution

Distribution:

The Big-headed ant now has a world-wide distribution. Within Australia it is widely distributed throughout the east coast, and the south-west corner of Western Australia. It occurs patchily throughout the remainder of coastal southern Australia, and northern Australia. It is also known in many isolated towns, such as Alice Springs, Camooweal and Mount Isa. This ant can exist wherever human disturbance is present (towns, mines, camping sites) and in natural areas that are well shaded and/or humid, and therefore has a potential distribution throughout all of Australia. It is most likely to be unrecorded from a great number of localities throughout Australia. (NSW, QLD, VIC, SA, WA, NT; Christmas Is).

Features:

Pheidole is the second largest genus of ants in the world, and identification of species such as Pheidole megacephala is often extremely difficult. It is a small ant (minor workers approximately 2 mm long and major workers 3–4 mm long), ranging in colour from a pale yellow to a very dark brown. Major workers are distinguished from minor workers by their disproportionately large heads. The first antennal segment, or scape, of the minor workers extends far above the top of the head, and is covered in many long hairs. There are no spines on the front of the body (the pronotum), but two very small spines on the rear of the body (the propodeum) facing almost directly up. There are many small punctations (pits) on the rear side of the body, and side of the head, but remaining body areas are smooth and shiny. The entire body is covered in many sparse, long hairs. The second waist segment (post petiole) is conspicuously swollen.

Ecology/Way of Life:

Big-headed ants prefer moist, shaded areas, but will live in extremely dry environments by living in micro-sites such as the base of trees and under concrete. They are most active during the relatively cool parts of the day and night in tropical regions, and throughout the day in cooler temperate regions. These ants have very general feeding and nesting requirements. They will eat anything and nest predominantly underground, but will nest within trees, especially in wet areas.

Workers from different nests do not fight with each other. As a result, interconnected super–colonies covering tens of hectares can develop. New colonies are not formed by a flight by a queen, as do most other ant species. Instead, a new queen and a small group of workers migrate to a new nest site within a few feet of the parent colony. A reproductive queen and at least ten pupae/minor workers are required for a new colony to survive. This ant is predominantly spread by people, particularly within the soil of potted plants.

This ant is generally extremely abundant when it is present, and will kill all other ant species within the area. Its colonies are very conspicuous by the large amount of soil brought to the surface and piled in mounds around the many nest entrances. Piles of bodies of dead workers may also be found near the nest entrances.

Preferred Image

Interaction with Humans/Threats:

Big-headed ants are a major threat to Australia's biodiversity due to their ability to kill all native invertebrates, particularly ants. Indirect evidence also shows that it negatively affects birds, mammals and reptiles, and can change the distribution of plants. Agricultural production is adversely affected directly through damage to fruit, and indirectly because this ant protects pest insects that decrease plant productivity, such as aphids and mealy bugs. This ant eats seeds, which makes it a pest in seeded crops and in areas undergoing rehabilitation. It is a domestic pest in buildings, particularly around electrical cables. It also chews through plastics, including drip irrigation tubing and telephone cable sheathing.

Other Comments:

Pheidole megacephala was named by Fabricius in 1793. The genus name is from the Greek: pheidole = thrifty, which describes well the tireless and economically laborious collection and storage of seeds performed by many species in this genus; the species name comes from the Greek: mega = big; and kephale = head.

Further Reading:

Bach C.E. (1991). Direct and indirect interactions between ants (Pheidole megacephala), scales (Coccus viridis) and plants (Pluchea indica). Oecologia 87: 233 – 239.

Hoffmann B.D. (1998). The Big–headed Ant Pheidole megacephala: a new threat to monsoonal northwestern Australia. Pacific Conservation Biology 4: 250 – 255.

Hoffmann B.D., Andersen A.N. and Hill G.J.E. (1999). Impact of an introduced ant on native rainforest invertebrates: Pheidole megacephala in monsoonal Australia. Oecologia 120: 595 – 604.

Williams DF (1994) (ed). Exotic ants: Biology, impact and control of introduced species. Westview Press, Boulder, Colorado.

Acknowledgments:

Text, map and photographs by Ben Hoffmann, CSIRO Sustainable Ecosystems, Darwin.

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Images and Multi-media:  
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image/gif 49206 bytes Pheidole megacephala - pinned
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image/gif 81084 bytes Pheidole megacephala nest
Distribution Map  
image/gif 7988 bytes Distribution of Pheidole megacephala

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