We all make decisions every day, but are only rarely involved in`group-level' decisions, such as voting for a politician. When a bee swarm decides to move house, they also make a group decision, but Thomas Seeley,from Cornell University, explains that only a few hundred honeybees are actively involved in the process. Seeley and Kirk Visscher, from the University of California, are fascinated by the ways that insect societies organise themselves and they wondered how bees make the decision where to move next. The pair already knew that scout bees are the first to go off in search of promising nest sites. Having discovered a potential home, the successful bee returns to the swarm and communicates the location with a waggle dance to encourage other scouts to take a look before making the decision. But how do scouts communicate a potential nest site's desirability? Curious to know which aspects of a waggle dance encoded the crucial information, Seeley and Visscher set off for Cornell University's Appledore Island to find the differences between scout bee dances that report desirable residences and those that report cramped conditions ().
Arriving with a team of student observers at the isolated island, Seeley and Visscher prepared a swarm to go house hunting. Offering the insects a choice between a desirable (40 l) and a mediocre (15 l) nesting box, each situated within 250 m of the homeless insects, Seeley and Visscher filmed the scout bees' waggle dances when they returned to the swarm. Meanwhile, a pair of observers, each armed with paint and data loggers, waited patiently to mark individual scout bees as they arrived at each nest box and recorded the insects' arrivals and departures.
After filming scout bees from four swarms, Seeley and Visscher analysed the insects' antics and found that the first scout to find a site almost always danced vigorously, no matter how good or poor the site was.
Seeley explains that this is a critical stage of the decision-making process. If the bee doesn't announce her discovery to other scouts, then the site won't be entered in the bees' `debate'. So a bee discovering a site nearly always danced for it, regardless of its quality.
They also found that bees that visited the larger nest box tended to perform more cycles of the waggle dance than scouts that visited the smaller box; so the number of waggle dance cycles seemed to be the key factor in communicating which was the better of the two sites.
However, this wasn't always the case; sometimes bees performed a large number of waggle dance cycles even when they had only found the small box. Seeley explains that mistakes such as this aren't a problem for the bees,because so many scouts visit the site that the `noise' generated by the odd bee getting it wrong eventually averages out. The team also noticed that with each subsequent return to the nest site, the bees performed fewer and fewer waggle cycles until they eventually stopped waggle dancing altogether,naturally limiting the influence that individual bees have on the decision-making process.
According to Seeley, the bee swarm's decision-making process is much like that of monkey brains: both accumulate evidence for multiple alternatives until the evidence for one reaches a critical level, when it becomes the chosen alternative. He explains that the bees do this by recruiting scout bees to visit each potential site until the number of scouts at a site exceeds a threshold. The decision is made when the bees sense the `quorum' at the site and return to the swarm to spread the good news.
