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WOULD you consider buying a house without ever setting eyes on it? An economist I know did just that. He simply drew up a list of desirable characteristics, gave it to his estate agent and retired to his ivory tower. As soon as his ideal home turned up he reappeared, cheque book in hand. Personally, I trust my gut reaction to tell me when a place is right. But however you do it, choosing a new home is a complex business. And the more family members you have to please, the trickier it gets. So spare a thought for the honeybee.

In the late spring or early summer, when food is plentiful, a hive can quickly become overcrowded. Then a mother queen will up-sticks, taking half the workers with her. This swarm of perhaps ten thousand bees will settle in a dense cluster under a nearby branch, and from this temporary resting place, several hundred scout bees set off in search of a new home. They are looking for a hollow in a tree, or a similar cavity, with a volume of at least 20 litres. It should have thick, strong walls and an opening no bigger than 30 square centimetres, at least three metres above the ground and south facing. The scouts may find a dozen or more alternatives that more or less fit their real estate requirements, but within a couple of days they are all agreed upon a single location. Then the whole swarm lifts off, following the scouts, and the housewarming can begin.

Between them, these several hundred scouts seem to make a good decision, and very quickly. Considering that each bee has a brain about the size of a grass seed, where does this collective wisdom come from? Intriguing new research shows that bees鈥� house-hunting tactics may be simpler than anyone had imagined. To find out how scout bees reach a consensus, Tom Seeley from Cornell University has been watching them perform elaborate waggle dances to advertise possible nesting sites to the other scouts. He concludes that the scouts reach a collective decision without comparing alternative sites and without any one bee having to coordinate the proceedings.

We鈥檙e more familiar with the symbolic waggle dance as a way of telling other bees where to find food. In a pioneering series of experiments over half a century ago, Karl von Frisch of the University of Munich deciphered the 鈥渓anguage鈥� of the dance. A worker bee returning from a source of nectar or pollen more than 100 metres from the hive will mark out a figure of eight on the vertical honeycomb wall. At the crossover point she dances forward, buzzing and waggling her abdomen. The angle of this waggle run from the vertical gives the angle of the food site in relation to the Sun as seen from the hive (see Diagram), and the bees know how far away the food is by how long the waggle run lasts.

The first clue to how scout bees used this dance when deciding where to live came in the mid-1950s. Martin Lindauer, a colleague of von Frisch, discovered that scouts report the location of potential nest sites, using the side of the swarm as a dance floor instead of the wall of the honeycomb. He also noticed that although the scouts start out advertising several sites, all the dancing will eventually be for a single site. He suggested that the bees were influencing one another, but until now no one could say how. The bees鈥� limited cognitive capacity made it unlikely that scouts were directing each other to potential nest sites, comparing notes and then trying to persuade and cajole each other into opting for a unanimous verdict like members of a jury. So how do the bees decide on a new home?

To find out, Seeley and his student Susannah Buhrman tagged all 4000 bees in a swarm with a number and a colour code. No one has ever tried this approach before. 鈥淧eople didn鈥檛 take the trouble-it鈥檚 a lot of work,鈥� says Seeley. 鈥淎 person can label about one bee a minute.鈥� But after around 66 person-hours of painstaking work, the researchers could simply sit back and watch the swarm.

First, the scouts spend a day or so gathering information. They scour the surrounding environment for possible nest sites and then begin dancing, but do not come down strongly in favour of any one. Next comes the decision-making period. Sites advertised only weakly and briefly will soon fall by the wayside, but more popular sites can provoke a real 鈥渄ebate鈥� among the dancing bees (see House hunting). 鈥淓ventually,鈥� says Seeley, 鈥渁ll the dances being performed centre on one site. They鈥檝e built a consensus.鈥�

By tracking the behaviour of individual bees, Seeley and Buhrman made a crucial discovery about how this consensus comes about. Surprisingly, although the scouts may stop and restart dancing, most bees do not switch allegiance to a different site. Instead many of the scouts simply drop out and do not dance again, so less popular sites with fewer dancers will rapidly lose all their support. 鈥淭he process of building a consensus among dancing bees relies much more upon bees ceasing to dance than upon bees switching their dances to the chosen site,鈥� explains Seeley. This seemingly trivial observation means that the decision-making process will never become deadlocked, with unyielding scouts dancing for two or more sites.

Even those few bees that do change allegiance-perhaps 20 per cent of the scouts-do not seem to be directly persuaded by another bee. After dancing for an unpopular site, they seem to drop out of the dance for several hours before regaining their enthusiasm and joining in with the dancing for another site. But the change of heart does not seem to come from visiting a new site. Seeley鈥檚 experiments suggest that most scouts visit only one potential nest site while the swarm is house hunting.

Another study, by Kirk Visscher from the University of California, Riverside, and Scott Camazine from Pennsylvania State University, confirms that individual scouts need not actively compare potential nest sites while making their decision. The team set up two identical nest boxes in an area of the Californian desert with no natural nest sites and then marked each dancer according to the box she first visited. From the marks the researchers pinpointed the small number of bees that visited both boxes. In some of the experiments they took away these bees, but in others they let them return to the swarm. Either way, swarms took an average of around 13 hours to reach a consensus. What鈥檚 more, over 80 per cent of bees visited only one box. 鈥淭hese findings point in the direction of direct comparison not being a very important part of the process,鈥� says Visscher.

Using the same setup, Visscher and Camazine showed that when bees do switch allegiance, it is because the scout bees simply pick up and copy other dances on the swarm in proportion to the total amount of dancing by other scouts for these sites. 鈥淲e videotaped and transcribed all the dances on the swarm,鈥� says Visscher. 鈥淲e then looked at all the dances that a bee could possibly watch after her own first dance-that is, all the dances that occurred after the time of her first dance.鈥� They calculated how long scouts would be likely to spend following dances for each site if they simply copied dances at random, and measured how much time they actually did spend dancing for each. 鈥淭he distributions were a very good match,鈥� says Visscher, 鈥渟uggesting that bees just follow dances at random as they encounter them.鈥�

If most scouts see only one potential site, and any subsequent dancing on the swarm is random, might they not end up choosing an inferior home? Seeley and Buhrman could not tell if this was the case in the study where bees were individually marked, because they focused on the swarm and did not follow the scouts out into the surrounding countryside. Instead, they tested the idea in a more controlled environment. On the bleak, treeless Appledore Island, off the coast of Maine, they gave their bees a choice of five nestboxes with identical specifications, except that one had an ample 40-litre capacity and the others a meagre 15 litres. The best site was not found first in any of the three trials, yet in all cases it was the final choice.

Seeley suspected that scout bees must adjust their dance to tell the swarm about the quality of potential nest sites. He had discovered that the waggle dance carries information about the quality of a flower patch. 鈥淚t suggested the same thing might be happening here,鈥� he says. Recently, he and Buhrman found the dance indicates the quality of nest sites in at least two ways. They offered the swarming bees a choice of an excellent and a mediocre nestbox and made video recordings of the dances for both. Dances for the excellent site turned out to last longer and each dance circuit was shorter. 鈥淢ore waggle runs in total is the key thing,鈥� says Seeley.

Things were beginning to fall into place. Even bees that are dancing for the winning site eventually tire and stop. If they resume dancing, they need do nothing more sophisticated than copy another scout at random. As long as the highest quality sites elicit the most vigorous dancing, with the most waggle runs, a bee that starts dancing again is simply more likely to spot a bee dancing for a high quality site, and eventually the best site will get unanimous backing. 鈥淧ositive feedback is the key to one site becoming the leader,鈥� says Seeley. 鈥淚t鈥檚 a snowballing process.鈥� Because the quality of the site shapes dancing behaviour, bees don鈥檛 need to do anything complex like comparing alternative sites, all they need is knowledge of one site at a time and the ability to loose interest in that site and later follow another bee鈥檚 dance to advertise a fresh site.

But how do bees know a good home when they see one? The evaluation process is still largely a mystery. Scouts can certainly take direct measurements. Using an ingenious setup with treadmills, Seeley has shown that bees can assess the volume of a potential home. 鈥淚t is based on the amount of walking they have to do to circumscribe the cavity,鈥� he says. Even so, it seems unlikely that bees are behaving like our rational economist or his estate agent, ticking off desired attributes from a real estate wish-list. It may never be possible to show how a bee integrates all the information that it collects about a potential nest site, but Seeley believes that what鈥檚 happening is more likely to resemble the gut-reaction approach-not so much calculated as instinctive. 鈥淚t鈥檚 almost certainly the case that somehow a scout is getting an overall sense of `goodness鈥�, which is stimulating some part of its brain,鈥� he says. 鈥淚n a lot of cases we have these gut summaries, and they are probably even more important for bees.鈥�

From a human viewpoint, it seems amazing that more than 100 individuals, especially ones with such tiny brains, can reach a consensus in a matter of hours. But Seeley points out that bees are only doing what comes naturally. They take advantage of their large numbers to investigate several alternatives simultaneously then make a virtue of the fact that no one individual could possibly coordinate the proceedings. The decision-making process is highly decentralised, yet by following a few simple rules, limited individuals with tiny brains combine to create a superorganism able to make sophisticated and accurate decisions. 鈥淲hat the whole swarm does is very amazing,鈥� says Seeley, 鈥渂ut when you break it down and see what each individual bee does, it鈥檚 more believable.鈥�

Further reading:

Group decision making in a swarm of honey bees by Thomas Seeley and Susannah Buhrman, Behavioral Ecology and Sociobiology, vol 45, p 19 (1999)

Thomas Seeley presented his results at the Dahlem Workshop on Bounded Rationality held in Berlin earlier this year. Results from the workshop are due to be published as a book by MIT Press in February 2000

Collective decisions and cognition in bees by Kirk Visscher and Scott Camazine, Nature, vol 397, p 400 (1999)

Communication among social bees by Martin Lindauer, Harvard University Press (1971)