“They’re able to float to a new location and set up a colony, and it’s a sign that fire ants are reaching a certain density when they’re able to do that,” he said.

“We’re starting to see parks and school playgrounds closed down by fire ants. We’re also seeing fire ants close down beach accesses … because they’re able to inhabit the upper dunes on some beaches.”

Fire ants, which are native to South America, were introduced to the US state of Alabama in the 1930s. They have since spread across America’s South, where more than 80 deaths have been recorded. Their bite typically causes a burning sensation that lasts up to an hour and, in some cases, a fatal anaphylactic shock.

The insects are capable of establishing colonies in 99 per cent of mainland Australia, and a nationwide infestation is feared if the ants enter the Murray Darling Basin network and form rafts in the river system that extends from Queensland across NSW, into Victoria and South Australia.

The federal government is co-ordinating a national fire ant eradication program, with plans for a $600 million effort in Queensland to reduce the threat to the nation – but Western Australia, South Australia, Tasmania and the Northern Territory are yet to commit their share of the funds.

“The fire ant eradication treatment area forms a horseshoe around the infestation – spanning from Moreton Bay in the north, west to the Lockyer Valley and south to the Gold Coast near the NSW border,” a spokesperson for the national eradication plan said.

Federal Agriculture Minister Murray Watt said the plan would double the size of the treatment and surveillance areas, and add 350 workers and aerial eradication capacity to the current regime.

Fire ants are copper brown with a darker abdomen. They are relatively small and measure 2 to 6 millimetres, with a variety of sizes in each nest.

Their nests are usually found in open areas such as lawns, garden beds, near water sources and along roads, and can appear as mounds or flat patches of loose soil with no obvious entry and exit holes.

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