Piping-hot Scout Bees in Swarms

Introduction

The nights are cooling down here and a couple of colonies have stopped maintaining high brood nest temperatures which I expect indicates reduced egg laying by the queens. I’ve checked on top insulation and sealed up any gaps in old boxes with Duck tape (brand of Duct tape) pinched from Linton’s garage when my Gorilla tape ran out. The wasps are still a nuisance but they have not compromised any colonies. I’ve had about five traps around the apiary.

The Himalayan balsam is still flowering down by the river and the Eucryphia spp. tree in the garden also continues in bloom six weeks on. Butterflies visit it and the sun remains fairly warm. Tremendous gales rattled the trees yesterday and the lawn is covered in torn leaves. The birch trees are turning a delicate gamboge and autumn is here for sure.

Yesterday, I saw the first skein of geese come down from tundra lands in the north, and the red squirrels are back at the bird feeder. They have their own feed box which I filled yesterday with peanuts in their shells.

It’s a good time to be thinking about tropilaelaps (I use its common name so haven’t capitalised it) which has reached Crimea and Georgia and may even be in Turkey. I recently signed up for BEE-GUARDS newsletter and there is a really useful webinar about it here https://beeguards.eu/

It’s also a good time to be thinking about imminent swarms if you live in the southern hemisphere. And here in the northern one we have around eight months before we have to prepare for our next swarm season. We can be even better prepared after reading this great guest blog by Professor Tom Seeley. Once again, I thank you, Tom, for contributing to the Beelistener and sharing your experience and knowledge with us. 

Piping-hot scout bees in swarms

              I suspect that whenever you have come to a swarm of bees with the aim of collecting it, you have wondered whether you must work quickly, to get these bees into a hive before they fly off, or instead you can work slowly and carefully in snagging this swarm.  

Fortunately, the bees in the swarm make it easy for us to know whether they are, or are not, getting ready to launch into flight.  To find out if they are preparing to fly off, put an ear within 10 cm (4 inches) of the swarm cluster and listen to it.  If you hear high-pitched sounds that are similar to the rising engine whine of a race car that is rapidly accelerating, then you can be sure that this swarm is indeed preparing to fly away.   In this case, you should proceed directly to shaking this swarm’ into an unoccupied hive. 

              The high-pitched sounds that you have heard are called piping signals. They are produced by the nest-site scouts in the swarm when they sense that their process of choosing the swarm’s new home site has reached a conclusion.  The piping scout bees are informing the non-scout bees in the swarm that the time has come for them to warm up their flight muscles.  Doing so is a critical part of the swarm bees’ preparations for launching en masse into flight and then traveling together to their new dwelling place.  Fig. 1 shows how a nest-site scout produces a piping signal by pressing her thorax onto a surface—shown here as a wooden board, but normally it is the body of another bee—and then pulling her wings tightly together over her abdomen while activating her flight muscles.  This produces powerful vibrations of her body.  These vibrations pass into whatever object (usually another bee) that she is pressing her thorax against.  These vibrations also pass into the air.   This is why we humans can hear the scout bees’ piping signals.

              In August 2000, I was joined by Dr. Jürgen Tautz, a professor at the University of Würzburg in Germany, to video record the sights and sounds of the nest-site scouts when they producing  a mixture of piping signals and waggle dances on the surface of a swarm.  Our investigation involved holding a tiny microphone, fixed to the end of a dowel, over worker bees (one at a time) that were producing piping signals.   When I played back these video recordings in slow motion, and made detailed time lines for each piping bee’s behavior, I saw that these energetic bees often switched between worker piping and waggle dancing as they dashed over the surface of their swarm’s cluster.  An example of this frenetic signal production is shown in Fig. 2.  It shows how one nest-site scout switched between worker piping (black dots) and waggle dancing (zigzag marks).  The tick marks along her track denote 1-second intervals.  My 62-second recording of this scout bee’s hyperactive behavior began 2 minutes and 45 seconds before her swarm launched into flight.  Meanwhile, a few dozen other nest-site scouts were also dashing over and boring into the swarm’s cluster and sending piping signals to their swarm mates.   It was an awesome sight-and-sound show!

              Once Jürgen and I had studied the behavior of individual nest-site scouts as they produced their piping signals, we decided to check our hunch that the function of this signal is to stimulate ALL the bees in a swarm to prepare for takeoff.  The main preparation that every bee in a swarm must make is getting her/his flight muscles warmed up to about 35°C (95°F); this makes it possible for all the bees to launch into flight almost simultaneously.  We tested our hunch about the function of worker piping by seeing whether or not worker piping occurs only in the final hour or so before a swarm’s takeoff.  This is when all the bees in the swarm are preparing for the flight to their new dwelling place.  So, we measured simultaneously the level of piping in a swarm and the temperatures in its core and in its outer layer of bees.  It was essential that we started making these temperature readings several hours before a swarm took off and that we continued to do so throughout the swarm’s liftoff.   

Fig. 3 shows an example of the pattern of worker piping and cluster warming that we observed.  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°), we heard no piping.  But then, starting about two hours before takeoff, we heard worker piping, but only intermittently.

              During the last hour before the takeoff, however, the sound of the piping was loud, for by then numerous workers were piping simultaneously.  At the same time, the temperature in the swarm’s mantle (outer layer of bees) was rising rapidly.  Then, just when the temperature throughout the swarm reached 37°C (99°F), all the bees launched into flight!  This took less than 60 seconds.  The fact that worker piping coincides perfectly with swarm warming—both phenomena rise together to a climax at takeoff—tells us that the piping signal functions to stimulate all the bees in a swarm to prepare for takeoff by warming their flight muscles.

I think that the honey bee’s piping signal is very handy for beekeepers, as well as for the bees.  It makes it easy for us to know in advance when a swarm is on track take off and fly away.  If you put an ear beside a swarm—say, 4 inches/10 cm from its surface— and you hear a high-pitched chorus of nest-site scouts producing their shrill piping signals, then you can be sure that the swarm’s liftoff is imminent.  Fortunately, it is easy to impede the take-off of a swarm at which the scout bees are producing piping signal and are running across its surface buzzing their wings to trigger its liftoff.   All you have to do is lightly spray the swarm with water.  This will cool the bees and give you enough time to don a veil and present the bees with a fine new home…. your empty hive!

To learn more about the wonderful behavioral skills of nest-site scouts, see Chapters 3-9 in my 2024 book: Piping Hot Bees and Boisterous Buzz-Runners. Princeton University Press.