Small Package, Big Pest Scarfing Australian birds' eggs, lizards and insects, the fire ant is the least popular immigrant on six legs

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As far as uninvited guests go, australia's attention in the past few years has been focused on the arrival of human asylum seekers. But in the meantime a truly insidious migrant managed to slip in undetected: Solenopsis invicta, a species of South American fire ant with a potentially deadly bite, a ferocious temper and an appetite to match. Experts think it could out-pest all the other imports they have been fighting for the past century. "Fire ants are worse than rabbits, cane toads and cattle ticks. I can't think of anything we've had in Australia like this before," says Commonwealth Scientific and Industrial Research Organisation ecologist Bob Sutherst. "I call them the pest from hell."

Native to South America, the ants were first spotted in Queensland in February. Since then, nests have been found at 737 sites in 36 Brisbane suburbs, covering an area of around 40,000 hectares. So far they've been reported outside that known infested zone only once-in pot plants sent to Victoria that authorities say were caught just in time. But Sutherst's research indicates the ants could survive almost anywhere in mainland Australia. And they're quite happy to hitch-hike in soil. "All it takes," says Sutherst, "is one truck going to Melbourne."

The ants look ordinary enough: reddish-brown and 2-6 mm long. But they're named for the pain of their bites, which itch and blister, and, in rare cases, can cause a fatal allergic reaction. They eat insects and birds' eggs and even kill small animals like lizards. Size doesn't scare them, says Keith McCubbin, director of Queensland's Fire Ant Control Centre: "They'll attack anything that's on the ground."

In Brisbane, fire ants have already hijacked that Australian icon of leisure, the backyard. Some residents have stopped mowing and gardening. Others have sent pets to stay with friends. One family with 47 nests have moved their trampoline so their children can jump onto it from the back steps. "The thong [rubber sandal] might become a thing of the past," says McCubbin. "You can see the ants really changing the way we use the great outdoors."

And it's not just the backyard: in the U.S., fire ants cause millions of dollars of damage every year as they munch through wiring and destroy electrical appliances. Then there's the threat to agriculture from bite-blemished fruit and ant-devoured crop seeds. Early estimates in Australia predict that, if uncontrolled, fire ants could spread over 600,000 sq. km in 30 years, causing more than $A6 billion in damage. Much hangs on an eradication campaign that begins later this month, as the ants start foraging in warmer weather. The plan, part of a $A123 million national fighting fund, is to bait every backyard in Brisbane's infested patch. Hopes are high that the outbreak is still small enough to control. If not, these tiny invaders may soon be ruining more than just suburban barbecues.