South American fire ants are using floods to spread in Queesland

Tracey Ferrier |

Authorities are on alert amid evidence invasive fire ants might have harnessed the recent floods to expand their Australian invasion.

Eradication officers in Queensland have captured photos of the dangerous ants forming floating rafts with their bodies.

It’s one of the pest’s most impressive survival tricks. Thousands of ants lock their bodies tightly together, trapping air bubbles in the process and keeping them afloat.

Colonies can survive for weeks this way, with the multi-layered structures strong enough to keep rescued queens and their eggs, larvae and pupae safe and dry. The ants on the bottom also take turns to make sure they don’t drown.

When floodwaters eventually subside the rafts can be deposited in new areas, allowing the species to spread and further threaten ground-dwelling native fauna, agricultural activities and human health.

Dr Ross Wylie is the science leader with the $400 million National Fire Ant Eradication Program, tasked with dealing with the foreign invader native to flood-prone parts of South America.

“This rafting is one of the ways fire ants can colonise new areas, and this has been observed in southeast Queensland, including in Purga near Ipswich and around Logan,” he says.

“They can float for weeks until they come to dry land or a place where they can start a nest again.”

Dr Wylie says eradication officers always have to deal with a spike in fire ant activity reports after wet weather, and there are strategies in place to contain any new outbreaks.

“It is likely that the ants were there before the rain, but as they don’t tend to build their nests up in hot, dry weather, people weren’t aware,” he says.

“We plan for this type of thing and have teams on stand-by to the deal with any infestation that pops up. Alternatively, people can opt to engage a pest manager or purchase fire ant bait from a local retailer and treat their property themselves.”

Fire ant nests can appear as dome-shaped mounds or be flat and look like a small patch of disturbed soil. They also lack obvious entry or exit holes.