What are yellow crazy ants?

Named for their erratic, ‘crazy’ movement when disturbed, yellow crazy ants (Anoplolepis gracilipes) are a globally notorious invasive species that has the potential to cause significant impacts to the Wet Tropics World Heritage Area. Originating in South-east Asia, yellow crazy ants have been transported around the world via international trade and shipping. Their current distribution extends throughout the tropics, including Indian and Pacific Ocean islands, Papua New Guinea, and Mauritius. In Australia, yellow crazy ants have been found in Queensland, New South Wales, and the Northern Territory. Yellow crazy ants were first detected in the Wet Tropics in 2001.

Have you seen yellow crazy ants? Please report any suspected sightings to the Wet Tropics Management Authority at YCA@wtma.qld.gov.au, or call 07 4241 0525.

The yellow crazy ant is listed as one of the world’s top 100 worst invasive species by the IUCN and is listed as restricted biosecurity matter under the Biosecurity Act 2014. Yellow crazy ants do not bite or sting but can spray formic acid for defence or when subduing prey. Yellow crazy ants have a wide range of impacts on the environment, industry, and lifestyle. In large numbers, they can disrupt entire ecosystems.

The Wet Tropics Management Authority manages the Yellow Crazy Ant Eradication Program (YCAEP). Jointly funded by the Australian and Queensland Governments, the Authority aims to eradicate yellow crazy ant infestations from within and adjacent to the Wet Tropics World Heritage Area.

Why are they invasive?

Yellow crazy ants do not display aggression between colonies. This allows them to form super-colonies – very large, interconnected nests containing hundreds of queens and millions of ants. Without the need to expend energy competing with each other, these super-colony nests can use all their energy to fully exploit the resources in their environment, reducing food and habitat availability for native species.

• Do you live in an infestation area?

Because yellow crazy ants are polygynous (have multiple queens in one nest), their rate of reproduction can be very high. This contributes to colonies’ big appetites (often for native species!) and rapid colony growth and expansion.

Appearance

Yellow crazy ants can be recognised by their slender body, around 3-4mm long, and their long skinny legs. Their antennae are very long, as long or longer than the length of the body. The body is golden-brown with a darker brown abdomen that is sometimes striped. Yellow crazy ant behaviour is also distinctive: when disturbed, the ants run around quickly and erratically. Yellow crazy ants do not bite or sting humans.

Habitat

Yellow crazy ants prefer shady, moist areas, and will colonise a wide range of materials and habitats such as woody debris, tree bases, leaf litter, mulch, rock walls, pot plants, outdoor furniture, play equipment and even electrical appliances. They are also found in sugarcane and other crops. In the Cairns region, yellow crazy ants have been found in a variety of habitats including residential, industrial and bushland areas.

Foraging

In suitable weather conditions worker ants will forage both day and night. Yellow crazy ants are generalist feeders and ready scavengers and will consume a wide variety of foods. Their diet ranges from nectar, honeydew and fruit to invertebrates such as worms, grubs, insects and spiders, and small vertebrates including frogs, nestling birds, and lizards. Yellow crazy ants are particularly attracted to sugar and will farm aphids, whiteflies, and other sap-sucking insects for the sugary honeydew they secrete. While most workers forage within a few metres of their nest, workers have been known to travel over 29 metres from the nest to find food.

How are yellow crazy ants spread?

Yellow crazy ant queens disperse by ‘budding’. In this mode of spread, a queen will start a new nest by walking out of her original nest with some workers to start a new colony several meters away. Through this method, infestations can expand by up to 100m per year. Infestations can also spread more rapidly when yellow crazy ants are washed downstream along waterways.

However, the most important mode of yellow crazy ant spread is human-assisted movement. Yellow crazy ants can easily be spread great distances by people. Movement of infested vegetation, soil and machinery during farming activities, property development, pot plant trading and illegal dumping all have the potential to spread yellow crazy ants.