23.4.09

HOUSE HUNTING
ALA ANTS

Tiny radio transmitters were fitted to
ants by scientists to study their
house-hunting habits.

Researchers at the University of Bristol placed
radio-frequency identification tags to the
backs of the rock ants which measure
up to 3mm in length.

Two thousand of the tiny transponders would
fit on to a postage stamp.
The scientists then
watched the way the ants chose between
two nest sites to make their home.


The ants chose the superior nest even though
it was nine times further away than the
alternative, which was not as well built.


When a colony of rock ants needs to emigrate
to a new nest, scouting ants first discover
new nests and assess them before leading
nest-mates to the new nest to prepare it
before the rest of the colony emigrates.


Dr Elva Robinson, from the University's School
of Biological Sciences, said that 41% of the
ants that visited the nearer, poorer
nest later switched to the nest
which was further away.

Only 3% of the ants that first visited the far nest
switched to the near nest.
"Each ant appears
to have its own 'threshold of acceptability'
against which to judge a nest
individually," she said.


"Ants finding the poor nest were likely to switch
and find the good nest, whereas ants finding the
good nest were more likely to stay committed
to that nest.
When ants switched quickly
between the two nests, colonies
ended up in the good nest.


"Individual ants did not need to comparatively
evaluate both nests in order for the entire
colony to make the correct decision."


Dr Robinson said the study showed that
ants are better at house-hunting
then humans.


"On the other hand, animals - including
humans - who use comparative evaluation
frequently make 'irrational'
decisions," she said.


"The ants' threshold rule makes an absolute
assessment of nest quality that is not subject
to risks, so simple individual behaviour
substitutes for direct comparison, facilitating
effective choice between nest sites
for the colony as a whole."


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