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IN FOCUS: SMALL BROWN ANTS INSIDE BUILDINGS

A helpful, quick-reference guide to the most commonly encountered species of small brown ants found inside buildings.

 

The smaller the ant, the harder it can be to identify. When it comes to very small brown ants (less than 2 mm long), there are several potential species in Australia, including little fire ants, coastal brown ants (pictured above) and the various Monomorium species. However, only three of these nest indoors: the pharaoh ant, Monomorium pharaonis; the Singapore ant (previously Monomorium destructor, recently reclassified as Trichomyrmex destructor); and the coastal brown ant (Pheidole megacephala). This article will focus on the very similar pharaoh and Singapore ants.

The pharaoh ant is found Australia wide. Although it will nest outdoors in tropical areas, in many ways this ant could be considered a commensal pest – building its nests inside human structures over most of its range, and thriving in heated buildings. As a pest, “it just gets into things”, and with its wide-ranging diet it contaminates a range of food materials in both residential and commercial situations. It is known to transmit several serious pathogens such as Salmonella, Staphylococcus and Streptococcus, which means infested food needs to be thrown out. But of particular importance is the health issues they can cause in hospitals, where nesting conditions are ideal and plentiful food sources (including blood!) allow for pharaoh ants to become a serious problem.

The pharaoh ant is a small, light brown ant 1.5-2.0 mm long, with a dark brown/blackish abdomen. They have two nodes on the petiole (as do fire ants, coastal brown ants and other Monomorium species), but unlike fire ants and Singapore ants, pharaoh ants do not have a painful bite or sting.

 

Pharaoh ant (photo credit: Alex Wild)

Species Snapshot – Pharaoh Ant

Latin name: Monomorium pharaonis.

Common name(s): Pharaoh ant.

Description: Light brown ant, with a darker gaster. Very small, 1.5-2.0 mm long. Only active during the day, they can develop persistent trails.

Native distribution: Origin of the pharaoh ant is unknown.

Current distribution: Australia wide.

Nest location: Typically nests indoors in wall cavities, subfloors, near heat sources and electricaloutlets.

Nest structure: Multiple queens and multiple nests as part of the same colony. Budding can create building-wide infestations.

Diet: Highly varied diet (protein, oils and sugar). Known to switch between protein and carbohydrate food sources.

Sting/bite: Pharaoh ants do not sting/bite (humans).

 

With its widespread distribution, the coastal brown ant, Pheidole megacephala, can sometimes be confused with the pharaoh ant. As both species have two nodes on the petiole, this cannot be used as a distinguishing feature. However, the alternative name for the coastal brown ant – ‘African big-headed ant’ – gives a clue as to how to differentiate between the two species; the coastal brown ant has a major worker with an oversized head. However, the major worker is not always seen in foraging trails, which can add to the confusion. In addition, although coastal brown ants will sometimes nest in wall cavities, they more commonly nest outside, and their activity can be easily spotted as they dig up dirt in lawns and between pavers.

It is their nesting behaviour and colony structure which make pharaoh ants difficult to control. Individual nests can be quite small but colonies can consist of many nests and hundreds of thousands of ants. The colony expands by budding, meaning that there may be many nests in an infested building. Interestingly the queens only live for 4-12 months and even in the absence of a queen, workers can develop a queen from brood that is transported from the main colony. The bottom line is that with pharaoh ant control programs it is important to eliminate all the ants in all the nests within the building to eradicate the infestation.

Protein-based and sugar-based baits used in rotation can prove quite successful in pharaoh ant control, although repeat applications may be necessary. It is very important to place the baits near the foraging trails, as they develop very persistent trails. Non-repellent sprays can also be used to prevent ants coming inside. The use of repellent (pyrethroid) products is not advised, as they can cause the nest to fracture and bud. As such, whereas dusts applied to electrical outlets (where they like to nest) would be a standard approach for other ants, it is generally better to use baits with pharaoh ants.

The Singapore ant has a more limited distribution than the pharaoh ant and is primarily found in the tropical and sub-tropical areas of QLD, NT and northern WA. However, as its small nests can be easily transported, it has also been positively identified on occasion in the southern states. It is an invasive tramp ant and forms multi-nest, multi-queen colonies, sometimes numbering in their millions. In their native tropical range they nest both in the ground and in trees, although this is less common in cooler climates. They will also nest inside buildings, with a particular preference for electrical sockets. They typically expand their nest by budding although alates have been observed. They can often displace other ants species and native animals from an area.

 

Singapore ant (photo credit: Dan Schofield/iNaturalist)

Species Snapshot – Singapore Ant

Latin name: Trichomyrmex destructor (previously Monomorium destructor).

Common name(s): Singapore ant, destructive trailing ant, ninja ant.

Description: Light brown ant with a darker gaster. Polymorphic workers range in size from 1.8-3.5 mm. They develop slow-moving, long-lasting trails.

Native distribution: Probably originated in Asia or North Africa.

Current distribution: Many tropical and subtropical areas globally.

Nest location: Outside in soil and trees, but will readily nest inside buildings, particularly in electrical sockets and electrical equipment.

Nest structure: Multiple queens and multiple nests as part of the same colony. Colonies can contain millions of ants.

Diet: Highly varied diet (protein, oils and sugar), but particularly keen on protein and oily foods.

Sting/bite: Singapore ants have a painful bite.

 

Two of its other common names – the ‘ninja ant’ and ‘destructive trailing ant’ – give a clue as to its habits. The Singapore ant can give a very painful bite and is known to “sneak into rooms without being noticed”, covering people and pets whilst sleeping, delivering many bites. It is a very destructive ant, capable of chewing through a wide range of building materials, but in particular the insulation on electrical and communication cables, which can cause significant damage and building fires. Indeed with their mobile nests, they can also cause short-outs of car ignitions in vehicles parked overnight in infested areas.

Although the smallest members of the worker caste are less than 2 mm long, they have a polymorphic worker caste with workers up to 3.5 mm long. They are a light brown colour with a dark brown abdomen. They are slow moving, developing long-lasting foraging trails. They are generalist feeders, eating protein, oil and sugary food sources and are known to tend sap-feeding insects. Inside the house they will eat a wide range of foodstuffs.

The good news is that they readily take a wide range of baits, with corn- and protein-based granular baits a good starting point. Due to their multi-nest colony structure, several bait applications may be required. The use of non-repellent sprays is also an option, particularly in treating the exterior of the building to prevent entry. As they tend to nest around electrical areas, the use of dusts should also be considered if the nests can be located.

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