Listening to the Bees by Professor Tom Seeley.

Introduction.

As the active beekeeping season draws to an end in many regions of the world, most of us reflect on how we performed and how we can improve beekeeping management next year. I strive to better understand bee behaviour and biology and turn to the books and podcasts again as the days shortens and the weather drives me indoors.

I’m delighted to welcome back our regular guest blogger, Professor Tom Seeley from Ithaca, New York, to share an important part of bee behaviour related to swarming with us. Regard yourself honoured because this is a sneaky wee peek at part of Tom’s new will-be bestseller, Piping Hot Bees and Boisterous Buzz-runners:  Solving 20 Mysteries of Honey Bee Behavior, to be released next spring. This article is adapted from Chapter 6, titled Piping Hot Bees, in his forthcoming (Spring 2024) book. This book is published by Princeton University Press so keep a look out for it. You can pre-order from Northern Bee Books.https://www.northernbeebooks.co.uk/

Thank you, Tom, for sharing this with us and for the useful beekeeping tips at the end.

Piping Hot Bees.

Back in the summer of 1970, I had just graduated from high school and had a summer job at the Dyce Laboratory for Honey Bee Studies at Cornell University.  One of my work assignments was to help Roger A. Morse (Doc), the Professor of Apiculture at Cornell, perform a study of how the worker bees in a swarm monitor the presence of their queen while they are flying to their new home.  This study revealed that workers use the scent of the primary component of the “queen substance” pheromone —what chemists call (E)-9-oxo-2-decenoic acid—as the indicator of their queen’s presence in an airborne swarm of bees. 

While watching Doc’s swarms one at a time before each one took off to fly to its new home, I heard high-pitched sounds coming from each swarm over the hour or two before it launched into flight.  I had likened these sounds to the rising engine whine of a race car accelerating in a straight stretch of the racetrack.  It seemed likely, therefore, that these high-pitched piping sounds were signals from the nest-site scouts to the other bees in a swarm, and that their message was “Ladies, warm your flight muscles!”  But back in 1970, I never was able to identify which bees made these high-pitched piping sounds, because they seemed to come from inside the swarm cluster, thus from bees that were out of sight.

The clarification of which bees in a swarm’s cluster produce the piping sounds came serendipitously in the summer of 1999, thus 29 years after I first heard them.  This discovery started with a chance observation that I made at my cabin beside Ox Cove, up in Pembroke, Maine.  I had set up a swarm on a wooden cross (Fig. 1) and had labeled with colorful paint dots the first dozen or so bees that performed waggle dances on this swarm. 

Figure 1.  A swarm, clustered on a wooden cross with a bottle of sugar syrup to keep its worker bees stuffed with food, hence well fueled for the flight to their new home.

These bees were nest-site scouts.  My aim was to watch closely the behavior of my color-coded scout bees, as part of a study of how the dissent among the scouts in a swarm gradually expires during the process of choosing their swarm’s new home.  (1)  On 2 August 1999, at 10:48 a.m., just five minutes before my swarm took off, my attention was drawn to scout bee Blue, who did something unexpected on the swarm’s surface:  she ran excitedly over other bees for a few seconds, then paused for about a second, grabbed a stationary bee and pressed her thorax against this bee, and then ran on, repeating the sequence of run-pause-press six times before she burrowed into the cluster and went out of sight (Fig. 2).  I noticed that each time scout bee Blue paused and grabbed another bee, she drew her wings tightly together over her abdomen and then she vibrated them slightly.  Was scout bee Blue producing the piping sound?  I had heard this sound each time she had grabbed another bee, but with just my “naked” ears I could not be certain that the sound came from her.  I needed a bee stethoscope.

Fig. 2.  A nest-site scout producing the piping signal.  During a pause from running over bees in a swarm cluster, she presses her thorax to the substrate (here a wooden surface), pulls her wings together over her abdomen, and activates her flight muscles to generate a vibration in the substrate.  In nature, the substrate will be another bee.  A nest-site scout will start to produce piping signals on the swarm cluster when she senses that a quorum of scouts has built up at “her” site.  From reference 1.

That afternoon, I drove to Morgan’s Garage in Pembroke and bought a 1-meter (3-foot) length of rubber vacuum hose that was about 6 mm (ca. one quarter of an inch) in diameter  This was a size that fit snugly in my ear.  I figured that I could use this as a sound tube to localize the sources of the piping sounds coming from my swarms.  A few days later, when I watched a second swarm and used my flexible rubber hose to listen in on another nest-site scout doing the run-pause-press behavior, I was thrilled to hear the exact same piping sound that I had heard 29 years before, while keeping watch over Doc’s swarms.

I was fascinated by the sights and sounds of the piping bees in swarms.  I was especially keen to describe their signal in detail and to test the hypothesis that nest-site scouts use the piping signal to stimulate the other bees in a swarm (those that are not nest-site scouts) to warm their flight muscles, in preparation for taking off and then flying to their new home.  A colleague from Germany, Jürgen Tautz, joined me in Ithaca in August 2000 to investigate the piping bees in swarms.  (2)  Jürgen came equipped with the miniature microphones and digital audio and video equipment we needed.  We set up a swarm on one side of a vertical board so that we could easily monitor everything that happened on the swarm’s surface.  Inside the swarm, we mounted two microphones and several temperature probes.  We also had a small, handheld microphone with which we could listen to sounds produced by individual bees.  Directly in front of the swarm, we positioned a video camera that recorded both the bees’ sounds from the swarm’s interior and the bees’ actions on its surface.  With all the microphone and thermometer wires leading from our swarm, a video camera continuously recording its activity, and two biologists hovering over it, our swarm looked rather like a patient in an intensive care unit. 

By now I had a precise search image for a piping bee—one dashing over the swarm’s surface but pausing frequently to seize a motionless swarm-mate—so I was able to spot pipers at a glance when we started to hear their shrill sounds.  From our video recordings, Jürgen and I quickly confirmed my observation that piping bees are exceptionally excited nest-site scouts.  These bees demonstrated this to us by switching between worker piping and waggle dancing while they scrambled over the surface of the swarm, as shown in Fig. 3.

Fig. 3.  Record of a nest-site scout switching between worker piping and waggle dancing as she ran over the surface of her swarm’s cluster.  Tick marks along her track denote 1-seond intervals.  Black dots mark piping and zigzags mark waggle dancing.  From reference 2.

At this point, Jürgen and I wanted to test the hypothesis that the function of worker piping is to stimulate all the bees in a swarm to prepare for takeoff.  The main thing that these bees need to do is warm up their flight muscles, so they are ready to launch into flight.  We tested this hypothesis by seeing whether or not worker piping occurs only in the last hour or so before takeoff, when all the bees in a swarm are making flight preparations.  For this, we measured simultaneously the level of piping in a swarm and the temperatures in the swarm’s core and mantle (its outer layer), over many hours prior to takeoff. 

Fig. 4 shows an example of the patterns in piping and warming that we found.  Three hours before takeoff, when the ambient temperature was 23°C (73°F) and the swarm’s core and mantle temperatures were 34° and 31°C (93° and 87°F), we heard no piping.  Then, about 90 minutes before takeoff, we began to hear worker piping, but only intermittently.  Finally, during the half hour before takeoff, the sound of the piping workers was loud, for by then numerous bees were piping simultaneously.  At the same time, the temperature in the mantle was rising, and just when the temperature throughout the swarm reached 37°C (99°F) the bees launched into flight!  The fact that worker piping coincides perfectly with swarm warming—both phenomena rise together to a climax at takeoff—shows that the worker piping signal functions to stimulate all the bees in a swarm to prepare for takeoff.

Fig. 4.  Pattern of worker piping (filled circles), swarm temperatures (open circles and triangles), and ambient temperatures (crosses) during the three-hour period preceding a swarm’s takeoff.  Only the nest-site scouts from the winning site produce piping signals.  From reference 2.

If you are a beekeeper, then it is very useful to know about the piping signal.  It will tell you whether or not a swarm that is hanging from a tree branch, stop sign, picnic table, or whatever, is about to launch into flight.  Simply put one ear within a few inches of the swarm.  If you hear a chorus of the high-pitched sounds of nest-site scouts producing their shrill piping signals, then you know that its liftoff is imminent.  But you can prevent it from doing so.  One way is to shake it immediately into a hive.  Another, and often better, way is to spray it lightly with cool water.  This cools the bees and buys you 10-15 minutes to don a veil and calmly present the bees with a fine new home… your hive!

References

1. Seeley, T.D.  2003.  Consensus building during nest-site selection in honey bee swarms:  the expiration of dissent.  Behavioral Ecology and Sociobiology.  53:417-424.

2.  Seeley, T.D. and J. Tautz.  2001.  Worker piping in honey bee swarms and its role in preparing for liftoff.  Journal of Comparative Physiology A 187:667-676.