|
NEXT time a swarm
of bees alights in your shrubbery, pause before you call out pest
control. For what appears to be an angry multitude of aggressive
stinging machines, may in fact represent the best example of harmonious
decision-making known to man.
What the swarm is doing, in the few days after
it has left the nest, is deciding exactly where to form a new colony.
But there are no leaders involved - the old queen that goes with
them takes no part in the decision. The worker bees scout the area,
locate all suitable nest sites, and reach a consensus among themselves
as to which one is the best. When they have decided, the entire
swarm suddenly lifts off and flies to the new site. How is the decision
made? Prof Thomas Seeley and Susannah Buhrman, from Cornell University,
New York State, have studied the process in meticulous detail and
what they have found is remarkable. These tiny-minded insects manage
to agree on the best quality nest site in the area without any single
bee having to assess the entire situation, or change its mind about
which site is best.
A swarm of honey bees (Apis mellifera) consists
of several thousand workers, and a single queen. They emerge from
the colony in a cloud, and soon settle on a nearby branch to begin
their conference. The environs are scoured for potential nest sites
by scout bees. ''Scout bees represent about three per cent of the
colony,'' explains Prof Seeley. ''They tend to be the oldest workers
in the swarm.'' You might think of them as the 'elders'.''
When a scout bee has found a site, it returns
to the swarm and communicates its findings to the other bees, by
way of the famous ''waggle'' dance.The direction and length of the
dance steps provide information about how far away and in what direction
the scout has found a nest site. And if the site is very good, the
bee will dance harder, and for longer, inciting other scout bees
to go and inspect this excellent home. Experiments with artificial
nest sites suggest that the swarm finds the available sites and
consistently chooses the best one.
Prof Seeley and Buhrman used swarms in which
every individual bee was marked with a number, and they videotaped
the entire process. ''What's marvellous about bees is that the decision
making is quite transparent,'' says Prof Seeley. From the videotape,
they could see which bees danced for which site, and monitor the
popularity of each site, relative to the site that the swarm eventually
flew to.
As they expected, at first there are bees dancing
for different sites. Then one site grows in popularity. More and
more bees dance for that site, until eventually all the scouts are
dancing for the same site. As soon as that happens, the swarm flies.
To understand how the bees always choose the best site, you need
to track the behaviour of individual scouts.
By painstakingly observing dozens of hours of
video-tape, the scientists first watched bees who began dancing
for a site that was not eventually chosen. They discovered that
these bees do not later change their minds and convert to the best
site. They simply stop dancing.
But the real surprise came when they looked
at bees who began dancing for the chosen site. Many of these bees
also stopped dancing before a decision was made. So the consensus
is not reached because the bees who have found the best site never
shut up. Instead, a scout bee is programmed to do its dance for
about a day and then to stop. ''The decision is made by a process
of differential recruitment,'' says Prof Seeley. More and more bees
visit the better site, because they have seen other bees dancing
so hard for it, until all the bees left dancing are just dancing
for one site. ''This is a very friendly way of reaching agreement,''
Prof Seeley adds. ''The scout bees do not compete aggressively with
each other.''
As humans, we are not very good at making group
decisions. We wrangle, debate, argue, and persuade, but we usually
end up resorting to a voting system, in which some people get what
they want and others have to go along with it. ''Bees gain a consensus
without any individual changing its mind or losing,'' says Seeley.
''This is a remarkable system to emerge from some very small brained
animals.'' Perhaps we ourselves have something to learn from the
way it works.
BACK
|