African big-headed ant or Coastal brown ant (Pheidole megacephala)

Pest Snapshot - Coastal brown ant (big-headed ant)

Scientific name: Pheidole megacephala
Identification: Brown / red ant with darker abdoment. Minor workers: 1.5 – 2.5 mm. Major workers up to 4.5 mm. Less common major workers have enlarged head..
Health threat: Low
Bite / sting pain: Does not sting, bite not painful.
Difficulty to control: Moderate – difficult
Diet: Prefers protein and oil
Nest locations: Gardens, wall cavities, roof voids
Colony structure: Mult-nest, multi-queen
Main pest season: Summer / Autumn
Indoor/Outdoor pest: Outdoors and indoors

Invasive / native:

The big-headed ant / coastal brown ant is one of the worlds worst invasive ants.

Distribution:

The big-headed ant is found worldwide in many tropical and sub-tropical areas. In Australia, it is common along the east coast, Perth and Darwin, but is probably more widespread.

It prefers moist, disturbed habitats – areas around human population are ideal. Typically, it nests outdoors in soil and under rocks / pavers. Sometimes it will nest indoors in wall cavities and plug sockets.

Colony size / structure:

A multi-queen, multi-nest species. The colonies can develop into massive super-colonies completely dominating an area. They are a highly destructive invasive species and will out-complete most other ant species.

Identification:

Colour: Mid brown / red
Size: 1.5 – 4.5 mm
Nodes on petiole: 2

There are minor and major workers, with the major workers (“soldiers”) having enlarged heads, from which they get their name. The major workers form around 1% of the foraging force, so may not always be visible.

Alates are not often seen as the colony expands through budding, whereby one or more queens with a number of workers move to set up another nest in a new location.

Food preferences:

Although big-headed ants are often seen tending sap feeding insects, they show a strong preference for protein and lipid foods. They will typically feed on live and dead invertebrates, but will eat any dead animal material.

Distinguishing features / behaviours:

The ants will move significant amounts of dirt to make their nests – their activity around pavers becomes particularly obvious.
Workers will travel significant differences between nest sites and to and front food sources.
They sometime build shelter tubes for foraging trails, which can look superficially similar to termite mud tubes.

Bite / sting:

The big-headed ant only has a mild sting which is not painful to humans and its bite is not painful.

Prevention tips:

Regular treatments (at least once a year) will likely be required to keep numbers down
Following good hygiene practices, especially clearing away food and not leaving pet food out, will help minimise any foraging inside buildings.

Other comments:

There are a number of other small brown ants, but the presence of major workers and sheer extent of infestations normally make identification straight forward.

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How to get rid of coastal brown ants - Treatment notes:

With most infestations resulting from large, multi-nest colonies, achieving complete and long lasting control is unlikely, as re-invasion will occur from surrounding areas.

Pest managers will use a combination of non-repellent residual sprays and granular baits can provide very effective in delivering a significant suppression of the population and exclusion of ants from buildings for a significant period.
Spraying the perimeter of buildings is effective in excluding ants from buildings.
Treatment of infestations in pavers can be applying into the gaps between pavers (by spraying or granular insecticides) or by treating the area with a suitable granular bait.
Lawn and sensitive areas can be effectively treated using granular baits. Even though it is a multi-nest, multi-queen species, granular baits appear to be very effective in eliminating nests within the colony.
Treatment indoors can also be achieved using a granular bait, although it may be necessary to grind up the bait to allow the ants to carry the bait through very small openings. The use of a bait station is advised.
Due to the size of infestations and need for specific knowledge and specialist products, professional pest services will generally provide the best results and most cost effective treatment.