Science and technology
Boom and bust
Invasive Argentine ants may be less persistent than once feared
Ready for take-off
DESPITE their name, Argentine ants are a well-travelled lot.
Human commerce has allowed them to hitch rides from their homeland to every continent on the planet, with the exception of Antarctica.
And when they arrive, they often thrive.
At least 15 countries now host colonies, which frequently prosper at the expense of native species.
This flexibility, combined with an aggressive temperament, makes them one of the world's best-known and most-hated invasive species.
Yet, as any general knows, establishing a beachhead is not the same thing as conducting a successful, long-term occupation.
Argentine-ant colonies sometimes collapse suddenly, and with no obvious explanation.
In a paper just published in Biology Letters, a group of researchers at Victoria University of Wellington, in New Zealand,
led by Meghan Cooling and Phil Lester,
describe their attempts to study such disappearances systematically.
The researchers examined 150 sites across the country where Argentine-ant nests had been recorded.
At 40% of them they found that the ants had vanished.
At many of the other sites, ant numbers were much reduced,
with areas that once sported dozens of nests over hundreds of hectares reduced to just one or two colonies covering much smaller tracts of land.
And with the invaders gone, native ants seemed to be re-establishing themselves,
suggesting that the Argentine ants' impact on biodiversity had been transient, rather than permanent.
A statistical analysis of the data yielded an estimate for the likely survival time of a typical colony of between 12.9 and 15.3 years,
and suggested that warm and dry conditions were more favourable for survival than cold, wet ones.
Exactly what caused the collapses is still not clear, although the researchers suspect that unfamiliar diseases may have played a role.
Unity is not strength
It is a plausible theory.
Because they grew from a small number of founder colonies,
因为它们是从很小的群体发展起来的，or possibly even a single one,
New Zealand's Argentine ants are genetically similar to one another.
That may be one reason for their success: ant researchers hypothesise that, being so closely related,
the individual insects are unable to distinguish their nest mates from members of other colonies,
which causes ants from different nests to co-operate as if they were kin,
and has led students of the field to speak not of hundreds of individual infestations, but of a single, country-spanning super-colony.
But a shallow gene pool can be a weakness, too.
If one nest proves susceptible to some environmental factor,
be it disease, predation, or even a cold snap or wet spell,
then it is likely that all the other colonies will share that vulnerability.
Now that they have documented the extent of the collapse the next step,
says Ms Cooling, is to test the hypothesis of genetic vulnerability and try to work out precisely what causes the sudden reversals of formicine fortune she has seen.
And it is not just ecologists who will be waiting for the results.
New Zealand's government had reckoned it might have to spend NZ$68m a year keeping the newcomers under control.
If Mother Nature can do the job instead, then it would represent a tidy saving for the country's exchequer.
Or mutate, into a more invasive plant than its wild cousin?
The enormous benefits of commerce between our two countries.
Yet there are other ways to prosper.
If the us gets more aggressive, then probably not.
Any sign of colony collapse disorder r?