Insect
invaders culled to preserve ecosystem.
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.
