How thousands of bees take to the air at once

Written by Thomas Hesselberg

Sunday, 15 July 2007

A honey bee worker visiting a flower. Courtesy of Photocase.com
One of the most impressive but also slightly terrifying sights in nature is the migrating bee swarm consisting of thousands upon thousands of individual bees moving in a coordinated and synchronised manner. Bee swarms form because the bees are searching for a new nest site and such swarms can be observed as a bundle of individuals clustering and remaining almost motionless in a tree for days with only single scouts bees coming and leaving, However, suddenly within a matter of seconds the entire swarm counting up to 10.000 bees will take to the air at once.

One might think that the queen bee was giving the command for departure, but bee queens, like ant queens, are little more than egg-laying machines. Instead scout bees that have successfully located a suitable nest site somehow are responsible for the departure. Exactly how this is done is what Kirk Visscher from the University of California, Riverside and Thomas Seeley from Cornell University wanted to find out. They observed that successful scout bees send out a piping signal upon their return and that this piping intensity increases prior to take off. To test whether this piping was relayed and thus copied by other non-scouting bees they presented a swarm of bees to a potential nest site and marked the scouting bees landing on the nest site to be able to identify them again when they returned to the swarm. However, they found no sign of the signal being relayed, scout bees and only scout bees piped.

They conclude that the piping signal in itself is not enough to trigger take off in the swarm but only functions as a priming signal. Instead they speculate that piping acts to excite bees, increasing their activity and thus increasing the temperature in the entire cluster. Once the temperature reaches the optimal conditions of the flight muscles for rapid take off (35º C) the bees take to the air in layers with the outer bees being followed rapidly by the new outer bees etc. Thus the scout bees do determine departure but in true democratic manner only those scout bees that have found a nest site which excites the entire bee swarm sufficiently will be successful.

Source: Visscher, P. K. and Seeley, T. D. (2007) Coordinating a group departure: who produces the piping signals on honey bee swarms. Behavioral Ecology and Sociobiology 61: 1615:1621.

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