Scientists in the tropical latitudes are chalking up their first victories in a long-running battle against marauding exotic ants. In one case, they have wiped out an invasion spread across 200 hectares in northern Australia, believed to be the largest ant eradication ever. "This proves it's possible," says Ben Hoffmann of the Australian science agency CSIRO, who led the attack.
Big-headed ant workers.
CREDIT: QUEENSLAND DEPT. OF PRIMARY INDUSTRIES
Aggressive imports such as fire ants and Argentine ants have been invading much of the world over the past 2 centuries, wiping out native insects and messing up local ecosystems. In Australia, where the ants are more recent arrivals, scientists from CSIRO and Parks Australia turned their firepower on an invasion of the African big-headed ant (Pheidole megacephala) in Kakadu National Park, a World Heritage site in the Darwin area in the Northern Territory. This creature eventually forms colonies of millions and wipes out other ants and many native insects, so it is a serious threat.
Starting in October 2001, teams of two to 24 people surveyed for ants and then blanketed colonies with hydramethylnon, a commercial poison that kills only ants. They kept surveying and reapplying for a year, aided by local landowners who gave them access to about 100 infested houses. In November, after 6 months of finding no ants, the scientists declared the zone ant free, Hoffmann reported last month at a meeting of the Ecological Society of Australia in Cairns. Total cost: 600 hours and $40,000, a tiny fraction of the millions it could cost to keep the ants down once they spread.
Entomologist Sanford Porter of the U.S. Department of Agriculture, who says the Australian campaign is probably the largest ant eradication ever, is working on a plague of little fire ants on 24 hectares in the Galápagos Islands. And Hoffmann's team has taken on a bigger challenge: an invasion of African yellow crazy ants (Anoplolepis gracilipes) in 65 locations around Nhulunbuy, also in the Northern Territory. That battle is expected to last 2 years and cost well over $1 million.
