What are yellow crazy ants?

The yellow crazy ant is listed as one of the top 100 worst invasive species by the IUCN and the Global Invasive Species Database. They are a category three restricted pest under the Biosecurity Act 2014. As such, all citizens have a general biosecurity obligation to minimise the risk of further infestation.

Read about the work we are doing to eradicate yellow crazy ants from the Wet Tropics World Heritage Area: YCA eNews September 2022.

Read the latest annual report card outlining our progress towards eradication to date: Report Card August 2021 (1.5MB)

Yellow crazy ants
Photographer: Jurgen Freund

Order: HymenopteraFamily: FormicidaeSubfamily: FormicinaeGenus: AnoplolepisSpecies: gracilipes


Identifying yellow crazy ants:

Yellow crazy ants are named after their distinctive erratic, frantic, movements when disturbed.

Identifying features:

    • Slender body, usually 4mm long (about half the size of a green ant)
    • Long skinny legs
    • Long antennae, equal to or exceeding the length of the body (11 segments in total)
    • Head is distinctly longer than broad
    • Golden-brown body, with a darker brown abdomen, sometimes striped
    • Day and night time foraging (they are less active in intense heat and heavy rain)
    • Spray formic acid (do not bite or sting)
    • Tend to be found in large numbers rather than by themselves.

Yellow Crazy Ant (YCA) workers with larvae
Photographer: Jurgen Freund

If you think you have seen yellow crazy ants, please call us as soon as possible on (07) 4241 0525. 

We rely on the help from members of the public to prevent yellow crazy ants from spreading. Your contribution in our efforts to eradicate this pest are greatly appreciated.

Lifecycle stages:

  • Eggs hatch after 18–20 days 
  • Worker larvae develop in 16–20 days
  • Pupae of workers develop in 20 days, while queen pupae develop in 30–34 days
  • Total lifespan of a worker ant is approximately 76–84 days.

Stages of the Yellow Crazy Ant (YCA) Life Cyle
Photographer: Mark Bloemberg

Origin and distribution:

While the exact origin of yellow crazy ants remains unclear, their current distribution extends through the tropical islands of the Indian and Pacific Oceans, including Papua New Guinea, Mauritius and South East Asia where they are a major pest. This broad distribution is undeniably linked to human movement activities such as cargo ships and trade which has ultimately led them to Australian shorelines. In Australia, yellow crazy ants are now present in a number of sites throughout Queensland and Arnhem Land. Specifically in the Cairns region, there are localised infestations in Gordonvale, Edmonton, Bentley Park, Bayview Heights and Russett Park (Kuranda), where yellow crazy ants are found in a variety of habitats including residential areas, sugarcane fields and rainforest.

How do yellow crazy ants spread?

Winged yellow crazy ant queens are not known to disperse by flying to new locations. Instead, colonies disperse by ‘budding’, a process where a queen leaves the colony accompanied by some workers and set off walking across terrain, or rafting down a creek to re-establish. Typically, the budding technique results in a relatively slow rate of dispersal, and manageable localised infestations. However, given the opportunity to hitch rides to new locations, yellow crazy ants can become established in other areas. In the Cairns region, yellow crazy ants are clearly taking advantage of human activities to spread, such as the movement of soil via construction and farming machinery, pot plant trading and illegal dumping. For this reason, if you live in an infested area it is crucial to dispose of your green waste and other rubbish appropriately (to your local tip). Re-location of green waste, garden items and skip bins in particular carry a high infestation risk.

Yellow Crazy Ant (YCA) Swarm nest
Photographer: Conrad Hoskin


Yellow crazy ants lack intraspecific aggression between closely related colonies (those that are genetically similar). Rather than establishing several competitive nests with individual queens (as majority of other ant species do), yellow crazy ants establish supercolonies—large interconnected nests containing multiple queens. Nests have been found containing hundreds of queens and many magnitudes more of workers. By cooperating, yellow crazy ants can successfully outnumber and displace other species, thereby dominating food and nesting resources.

This ant species falls under the subfamily ‘Forminicae’ because they do not have a stinger, and their pincers are notably reduced. In place of a stinger, yellow crazy ants have an acidopore (a small opening at the tip of their abdomen that sprays formic acid) as their defence and attack mechanism.

Habitat and diet:

In conjunction with maintaining strong collaborative behaviour, yellow crazy ants have the nesting and foraging habits of a typical generalist invader, which allows colonies to achieve high densities in a variety of habitats. For instance, ideal nesting grounds for yellow crazy ants range from woody debris, rocky substrates, tree bases, leaf litter, mulch, rock walls, pot plants, carports, pool filters and even electrical appliances such as air conditioners and televisions. Their omnivorous diet ranges from seeds and fruit to invertebrates (worms, grubs, insects, spiders) and small vertebrates including frogs, nesting birds, lizards and juvenile mammals when they attack in unison. Yellow crazy ants are a serious problem in sugarcane because of their strong mutualism with honeydew and nectar producing insects such as aphids and scales. The ants actively protect these insects specifically for the sweet sugary substances they produce (of which any residue transforms into mould that smothers the foliage), in return providing them with protection from predatory beetles.

Yellow Crazy Ant (YCA) on flower
Photographer: Conrad Hoskin

Yellow crazy ant
Photographer: Unknown

Yellow Crazy Ants (YCA) on hand
Photographer: Conrad Hoskin

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