Ants - invasive and pest

Red imported fire ant (Solenopsis invicta) (RIFA) is one of the most serious invasive ant pests in the world. It is native to South America and is known to be extremely aggressive. It can inflict painful stings on people, pets, and livestock.  

What to look for 

• hard to distinguish from common native ants 
• small (2 to 8 mm), red-brown coloured, with a darker abdomen 
• ants of many assorted sizes in one nest, with no visible entry holes
• usually aggressive if disturbed and can inflict a painful, fiery sting that can form blisters and pustules and, in some cases, anaphylactic allergic reactions. 

Where to look 

• around timber, logs, rocks, pavers, or bricks
• pot plants, topsoil, mulch, and potting mixes
• lawns, firebreaks, and fence lines
• untidy or overgrown areas or disturbed ground
• adjacent to buildings and other structures
• near dams, rivers, and ponds. 

View our short video to find out how a report made in 2025 by a local business enabled us to stop the invasive red imported fire ant before it spread, protecting Western Australia from one of the world's most invasive species. 

In 2019 RIFA was also detected in the Fremantle Port area. Following a 2-year comprehensive eradication and surveillance program by the department, WA was declared free of RIFA in October 2023.  

Help us keep WA free of red imported fire ant. Read our factsheet for additional information.

Argentine ants (Linepithema humile) are an introduced major pest ant species that are established in WA. They are commonly found in urban areas, where they can enter homes in search of food and moisture.  

They are very ordinary looking small brown ants and the most difficult common pest ant in WA to control as they can re-colonise quickly. 

What to look for 

• small and slender dark brown ants, 2.6 to 3.2 mm long 
• continuous well-defined trails of slow-moving ants  
• slight greasy, musty odour when crushed  
• can bite, usually painless. 

Where to look 

• urban areas 
• nests outside buildings, at the base (or in) trees  
• along the edges of paths and in lawns and garden beds  
• thrives in swamps and low-lying areas where moisture is plentiful. 

Coastal brown ants (Pheidole megacephala) (also known as ‘big-headed’ ants) are an introduced major pest ant species that are established in WA.  

What to look for 

• small, light ginger-brown coloured ants, with shiny dark brown abdomens
• two sizes — large numbers of worker ants (2 to 3 mm long) and a small number of ‘soldier’ ants (3.5 to 4.5 mm long), with a much larger head
• no obvious odour when crushed
• can sting but does not cause discomfort. 

Where to look 

• lawns and brick paving – look for lines of interconnected holes and small mounds of excavated soils
• enters buildings when populations outside are high
• ants may cover food put outside for pets, as they prefer fat/oil-based foods.