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Honey, I found us a new hive: how honeybee swarms collectively make good decisions

Photograph of a bee swarmHow a swarm of honey bees collectively decides on a new home and accurately picks the best one is shown in a paper published by an LSE researcher today (Friday 13 February).

Professor Christian List, along with Dr Christian Elsholtz, a mathematician at Royal Holloway University of London, and Professor Thomas Seeley, a biologist at Cornell University, show that a swarm's remarkable reliability in picking the best site stems from a sophisticated interplay of individual and collective decision-making amongst the bees.

Scientists already know that when a swarm is looking for a new home a few hundred 'scout bees' fly out to randomly explore potential nest sites. They then come back and perform a 'waggle' dance, with the duration of the dance indicating the quality rating they give to the site. Initially the scouts visit and inspect sites by chance, but once the dancing activity has built up, they are more likely to visit and inspect sites advertised by others. Eventually dance activity tends to converge and a consensus emerges*. Biologists have observed that the bees reliably find a high-quality nest site.

The researchers, whose paper is published in Philosophical Transactions of the Royal Society B, developed a computer model by which they could simulate the bees' decision making process in order to look at its individual components and work out why it is so accurate.

Photograph of Professor Christian ListProfessor List, a professor of political science and philosophy at LSE who works on social choice theory and mathematical models of decision making, explains: 'We found that it is the interplay of independence and interdependence between the bees that is so crucial to making a quick and good decision.'

The model shows that if the bees act solely independently, finding nesting sites but not advertising them, it slows the process down dramatically. Relying on the 'cosmic accident' of all the bees eventually stumbling on the same best site leaves the swarm homeless and vulnerable.

On the other hand if the bees act overly interdependently - blindly following the recommendations of other bees without checking the sites out for themselves - a consensus decision is rapidly made but there is no guarantee that it will be the best, or even a good decision.

Professor List said: 'The honey bees' decision procedure is remarkably sophisticated. The swarm manages to block and prevent the kind of "group think" that can bedevil good decision making.

'Humans, for example, demonstrate this kind of bad decision making behaviour when a number of investors, through random accident, buy stock in a company and others rapidly join in with the crowd, thinking that the increased demand for the stock indicates something real. This can result in a market bubble, where the price of the stock goes through the roof for no good reason and often with bad consequences.

'Looking at decision making processes in both humans and animals is very important. The need for collective decision making occurs almost everywhere in complex societies, and a good fundamental understanding of these processes can help design human organisations in ways that encourage good decision making.'

Cover of an issue of Philosophical Transactions of the Royal Society BProfessor List is joint editor of the current theme issue of Philosophical Transactions of the Royal Society B which looks at group decision making in humans and animals.

*On average, a honeybee swarm contains 12,000 bees. A typical decision making process takes about two days.


Notes for Editors

Copies of the paper 'Independence and interdependence in collective decision making: an agent-based model of nest-site choice by honeybee swarms' are available from the LSE Press Office, by contacting Sue Windebank, senior press officer, LSE, 020 7849 4624 or at s.windebank@lse.ac.uk

A full copy of the theme issue of Philosophical Transactions of the Royal Society B is available from the Royal Society press office. Please contact Cat Delange on 020 7451 2510 or at catherine.delange@royalsociety.org

Professor Christian List's webpage, with general information about his research, is available at: http://personal.lse.ac.uk/list/ 

13 February 2009