BioEd Online

Work has begun to save Australia's Northern Territory from one of the world's most vicious pests. Billions of yellow crazy ants will be poisoned in an attempt to halt the insects' trail of devastation.

Yellow crazy ants (Anoplolepis gracilipes), so-called because of their chaotic movements, are one of the world's most invasive species. The ants have lost the ability to form queens that fly away from the parent colony to form new communities elsewhere. Instead they form dense supercolonies as their numbers increase, with up to 1,000 ants per square kilometre of bush.

The ants were first spotted in northern Australia in 1990, but their numbers have been rising rapidly in the past few years. In Australia's northeast Arnhem Land, the insects have now infested 25,000 square kilometres of land - feasting on the local flora, and killing or out-competing resident invertebrate populations.

"Unless something is done, this could trigger the demise of the entire ecosystem," says ecologist Ben Hoffmann from the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO), which is spearheading the eradication campaign.

Local Arnhem Land ants are already in decline, says Hoffmann. "The crazy ants grab them and rip them to bits," he says. The gove crow butterfly (Euploea alcathoe enastri), which was thought to exist at just four locations in the region, is another casualty. Crazy ants invaded one of these regions several years ago, and since then the butterfly seems to have gone locally extinct.

The ants spray formic acid into their victims' eyes, blinding them and causing them to starve to death. As the ants' activities change the local flora and fauna, larger animals such as wallabies and possums could struggle for survival. Humans might also suffer. Ants and aborigines share some of the same resources, such as berries, says Hoffmann. So local people could see their food reserves diminished.

"This little ant will destroy our culture, our land, our life, so we need to kill it now," says Djawa Yunupingu, senior ranger for Dhimurru in northeast Arnhem Land.

Poison drop

"It's incredibly important to try to control the ants," says Dave Clarke, head keeper of London Zoo's invertebrate collection. People often underestimate the impact of invasive species on native ecosystems, but they can pose just as big a threat as habitat loss, he says.

Researchers plan to combat the ants by dropping granules of a specially designed poison onto the colonies from helicopters. The pellets, called Presto, contain a fishmeal product that ants love, but that other animals detest.

Hoffmann's team has already begun mapping the boundaries of the ant colonies, and aims to spread the pellets across three-quarters of the affected area within a year. The group hopes to have fully eradicated the ants from the region by one year later.

The poison has already yielded encouraging results on Australia's Christmas Island, where the ants have destroyed up to 20 million red land crabs (Gecarcoidea natalis) since 1989, triggering a 30% decline in the crab population. The approach brought the crazy ant population under control, while other animals have remained unaffected, says Hoffmann.

Yellow crazy ants are thought to have originated in Africa, then made their way to Asia and the Indo-Pacific hidden in packing materials and crates. Researchers suspect they first arrived in Arnhem Land during the Second World War, when American ships made frequent trips between Australia and the ant-rich South Pacific islands.