By Lynn Dicks
Swarming bees demons or democrats?
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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. |
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