Episode 41 of the podcast is now available! Listen on Podbean, or wherever you get your podcasts.
Chapter 7 (Initiating the move to a new home) of Honeybee Democracy tackles the question of honeybee scout signaling. How do scouts know when the swarm is ready to fly to their new nest site? How do they ensure readiness from their sisters who have been resting quietly? Do scouts use a consensus-sensing or quorum-sensing method to decide when the debate is over and it’s time to get moving? Listening in to learn the answers to these questions, and more!
Operation duckling flight!
Last Friday, I noticed 2 rather large ducklings by the side of a canal at a Towpath trailhead. They caught my eye because one was yellow-white, and I’ve never seen a wild duckling of that colour before. It’s also extremely early in the year to see such large babies, and I couldn’t shake the feeling that something wasn’t right.
I took a quick pic of them and reached out to people to get their thoughts on whether these were domestic breeds that had been dumped there. Sure enough, I quickly found out that they were indeed poor, dumped ducklings, and I resolved to rescue them.
The husbeast and I went out after dark and scooped the wee ones up. They didn’t even try to get away! I was so delighted to have been able to capture them so easily. We set up our ‘chicken hospital’, with some modifications for the ducklings (like a large bowl with rocks in it that they could splash in but not tip over).
We only had them for one full day (Saturday) as I was directed to a rescue organisation by a friend, and dropped them off with a volunteer on Sunday. They were in their new, secure home by Sunday evening, and will be ready for adoption once they have been vetted and quarantined.
In the short time I had them, I fell absolutely in love! Ducklings are so much more affectionate than my chickens, and they are so silly and fun. They’re definitely messy (which is why I have avoided them before) but I feel that it’s worth it now. It was hard to let them go but a little easier knowing that there will be ducks in my future. I am starting to research now and will then get an enclosure together! Stay tuned for a future episode all about different duck breeds and what to expect when bringing them home.
Huge thanks to Mid-Ohio Waterfowl Rescue, who helped me ID these babies (the yellow-white is a Pekin, and the brown a Rouen) and took them into her home to be cared for. Please check out her Facebook page for updates, and information on how you can help.
Hive Updates
Queen Macha's colony perished so now I am down to one colony (the Saskatraz-daughter hive). This was a particularly hard loss as I've had Macha since I bought the 2 nucleus colonies that got me started on this journey. She had survived one winter and I really hoped she would make it through a second. Cause of death was isolation starvation due to too small of a cluster, likely caused by varroa mite disease/virus transmission.
I treated my surviving colony with oxalic acid, thanks to my neighbour swinging by with his vaporizer.
Mite counts before winter are interesting to consult now. Macha and my OH queen actually had slightly lower counts than my only surviving colony so I really wonder what other factors were at play. This is why it's recommended to keep detailed notes!
Trying to stay positive despite all the loss. It is a challenge but I refuse to give up! Beekeeping is still, overall, a very rewarding experience for me.
And now, on to the book review!
Chapter 7: Initiating the Move to New Home
And so doth this soft shivering passe
As a watch-worde from one to an other,
Until it come to the inmost Bees:
Whereby it is caused a great hollownes
In the pomegranate.
When you see them do thus,
Then may you bid them farewell:
For presentlie they begin to unknit,
And to be gone.
-Charles Butler, The Feminine Monarchie, 1609
After a swarm leaves their mother-hive, it will fly as a great mass of thousands of bees before coming to rest in a cluster on a tree limb, fence post, or some other raised area. For hours or days, the cluster remains at this intermediary location while scout bees search for and then advertise potential nest sites.
Once a unanimous decision has been made, the swarm takes off once more to take up residence in their new home
This chapter will look into the mechanisms of what leads to this final flight home.
Preflight Warm-Up
This sections opens by introducing us to Bernd Heinrich, a gifted insect physiologist who studied the mechanisms of temperature regulation in honeybee swarms
Heinrich had been interested in this area of research thanks to two previous studies that found that the core temperature of a swarm could be maintained at about 35C/95F, the same as in the hive, and that worker bees must warm their flight muscles to at least 35C/95F in order to fly
As a hobby beekeeper himself, Heinrich also knew that worker bees will gorge on honey before swarming so that the swarm had a finite food source to provide energy for thermoregulation
He became curious as to the exact pattern of temperature within the swarm cluster, as well as how the bees control these temps and utilize their finite food source effectively
As a result, in the spring of 1980, Heinrich (then a professor at the University of California Berkeley) collected 14 natural swarms in the San Francisco Bay Area and brought them to the UC-Berkeley campus to study
To measure the swarm temperatures effectively, he used tiny electronic thermometers (thermo-couple probes), and to measure the metabolic rate, he used a cylindrical chamber of Plexiglass called a ‘respirometry vessel’
What Heinrich discovered thanks to this study provides key information on understanding how a swarm prepares for flight
He discovered that the swarm cluster’s core is indeed maintained at 34-36C/93-97F, regardless of the ambient temperature.
The outer layer, or mantle, of the cluster varies somewhat with the ambient temperature but is always maintained above 17C/63F, even if the ambient temperature drops below freezing
This temperature maintenance ensures that even the outer layer of bees are warm enough to remain active; if the temperature dipped below 15C/59F, the bees would enter ‘chill torpor’ and fall from the cluster, too cold to return or even warm themselves via shivering
Interestingly, Heinrich discovered that this thermoregulation process is not as energy intensive as one might assume.
At air temps above 10C/50F, the resting metabolism of the swarm (when the bees are not activating their flight muscles to generate heat) provides enough heat to maintain the core temperature at 35C and the mantle above 17C
Above temperatures of 20C/76F, the bees will spread themselves out to allow circulation of the air to cool the cluster to the needed temperatures
Similarly, if the mantle of bees begins to feel cool, they cluster more tightly together to trap the heat provided via the collective bees resting metabolism
Only once the air temperature drops below 10C/50F do the bees need to shiver to maintain steady temperatures
Heinrich, thus, discovered that the bees in a swarm have an effective method of temperature control, which also conserves energy resources
The bees that make up the mantle of the cluster reduce their need for active metabolism (shivering) by doing two things when temperatures are cold: maintaining their body temp just above that of the chill torpor threshold, and by primarily maintaining the needed temperature by huddling together instead of shivering
This discovery also demonstrates that the mantle bees are too cold to fly, which means that these bees must warm their flight muscles before the swarm can depart to its new home
Heinrich found that, just before the swarm takes off in its homeward flight, the temperature of the mantle rose to match the core temperature of 35C
Heinrich’s work was published under the title, “The Mechanisms and Energetics of Honeybee Swarm Temperature Regulation”
Ten years after this report was published, in June 2002, Seeley traveled to Germany to study the preflight warm-up behaviour of honey bees
Seeley collaborated with Jurgen Tautz, the director of the research laboratory that studied honeybees at the University of Wurzberg. They also worked with two of Jurgen’s graduate students, Marco Kleinherz and Brigitte Bujok
Together, their goal was to explore how the mantle of bees warm their flight muscles, using infrared cameras and computer software to convert the camera’s images into accurate temperature readings
Over two weeks, they recorded the temperature of mantle bees within a 10 x 10cm(4 x 4in) area on 2 swarms; starting from when the swarm first formed its cluster until the moment it flew towards its new nest site
As Seeley had observed previously, both swarms showed an unanimous agreement of the scouts’ dancing, causing scouts to become animated and moving excitedly
The infrared camera images showed something new, however; every bee’s thorax glowed with unusual warmth right before the swarm took flight
In fact, the percentage of bees with a thorax temperature of at least 35C grew exponentially in the last 30 minutes before flight. This means that all the bees in a cluster are hot enough for rapid flight
We know already that the bees at the center of the swarm cluster maintain flight ready temperatures, and with the rapid build up of warmth in the outer layer of the swarm, the entire cluster can disperse into flight within just 60 seconds
The questions this left Seeley with are thus: what caused the mantle bees to begin pre flight warm-up? What stimulated them to prepare for flight? And what was the final trigger that led to the entire swarm taking off into the air?
Let’s find out!
Piping Hot Bees
Seeley tells us that, 30 minutes before the swarm takes flight to its new nest site, you can hear a distinct, high pitched piping sound. At first, these sounds are spread out with one bee at a time making the noise. Over that final 30 minutes, however, an ever-increasing amount of bees join in until the noise reaches a crescendo, at which point, the bees take flight
Could this piping be a signal from the scout bees for their sisters to start warming up their flight muscles?
Seeley wanted to identify which bees start this piping. He had first become interested in this endeavour back in the 1970s, when he first began studying swarms as a graduate student
He felt that the noise originated within the cluster and so was unable to identify the bees that were piping
Martin Lindauer also failed to identify these bees back in the 1950s, stating “Now a hundred-fold high humming could be heard at the cluster, but I could not definitely find out whether this comes from the buzz-runners or from other bees.” Pg.155 (These ‘buzz-runner’ bees will be discussed later in the chapter.)
Seeley inadvertently stumbled across the answer to his quest in 1999 while working on his study that worked to identify how the dissent among scout bees ends (covered in the previous chapter, episode 40)
He was working with a swarm and had already labeled via paint dots the first few scouts that returned to the swarm to advertise, via dance, a discovered nest site
At 10.48am on August 2nd, just 5 minutes before the swarm would fly off to its new home, Seeley noticed one of his marked scouts, Blue, behaving oddly. She ran excitedly across the other bees for a few seconds before pausing and pressing her thorax against a stationary bee. Then she ran off to repeat this process of run-pause-press.
Looking closer, Seeley noted that when Blue grabbed another bee, she draw her wings tightly over her abdomen, and her wings appeared to vibrate slightly
Seeley could hear the piping sound but wasn’t confident that it was coming from Blue specifically
To solve this problem, Seeley used a 3ft piece of vacuum hose, about 6mm (¼ inch) in diameter, as a kind of crude stethoscope that allowed him to zero in on the sound
When he used this hose, he was able to ascertain that a scout being doing the run-pause-press maneuver was, indeed, making a piping sound!
To study this piping behaviour in depth, Seeley would need sophisticated recording equipment.
He enlisted the help of Jurgen Tautz to assist him in this work and so in August 2000, he came to Cornell from Germany, armed with miniature microphones, as well as digital audio and video equipment
The two set up a swarm in Seeley’s lab, positioning it on a vertical board for ease of observation. Inside the swarm were 2 small microphones and several temperature probes. Directly in front of the swarm was a video camera that recorded the bees’ activity as well as sound
“With numerous microphone and thermometer wires leading from it, a video camera continuously recording its activity, and 2 biologists hovering over it, our swarm looked rather like a patient in an intensive care unit.” Pg.157
Now that Seeley knew to look for a bee performing the run-pause-press activity, he was able to identify these bees as soon as the piping sounds began
Based on their video recordings, Seeley and Jurgen confirmed that these piping bees were extremely excited scout bees. In fact, these piping bees would switch between piping and enthusiastic waggle dancing, all while racing over the surface of the swarm cluster
Audio recordings revealed that each pipe is a single pulse of sound, lasting just a single second, composed of a fundamental frequency (the lowest frequency or ‘pitch’) of 200-250 hertz (cycles per second), plus many harmonies (repeats of the fundamental frequency) in the range of 400-2000 hertz. These high frequency harmonies are what makes the sound so shrill.
The fundamental frequency of the piping is identical to the wing-beat frequency of a flying bee; strong evidence that the sound is produced when a bee activities the flight muscles in her thorax, causing strong vibrations throughout her body
Seeley hypothesizes that most of this vibration energy is passed into the stationary bee that the scout holds on to and presses her thorax against, while some of that energy is ‘lost’ into the air, creating the sound that we can hear
Seeley and Jurgen were able to ascertain that the upward sweep in the pitch of each pipe is caused by the fundamental frequency going from 200 to 250 hertz, as well as an increase in the energy of the high frequency harmonics. They felt that this was likely caused by a piping be pulling her wings together and shifting her thorax, thus raising its resonant frequency
As interesting as all this is, all this hertz information is likely not entirely clear for many of us (me included) so let’s return to the original question behind this study: the function of these piping bees in readying a swarm to fly
Seeley and Jurgen first decided to ascertain whether piping occurs only in the last hour or so before flight, which is already known to be the time that the bees are making flight preparations via temperature increase
To do this, they measured both the level of piping in a swarm and the temperature of the swarm’s core and mantle for multiple hours before take off
They found that worker piping does indeed coincide with swarm warming!
Three hours before take off, the swarm’s core and mantle temps were 34C/93F and 31C/73F, respectively, with the ambient air temperature being 23C/73F. At this time, there was no piping,
90 minutes before take off, intermittent piping was heard. Finally, in the last 30 minutes before take off, the piping was now continuous and loud, and the mantle temperature began to rise
When the temperature throughout the swarm cluster reached 37C/99F, the bees all took off at once
As enlightening as this finding is, however, technically it only demonstrates a correlation between piping and swarm warming, not causation. There still exists the possibility that the piping was not the stimulus for the warming, and that perhaps there was some yet undiscovered signal that led to both.
One alternate theory is that bees use a ‘shaking signal’ to inform cool and quiet bees that it is time to prepare for flight. This signal is much as it sounds, with one bee grabbing another with her front legs and violently shaking her own body up and down for a second or two.
However, this shaking behaviour is seen throughout the entire house-hunting endeavor and does not seem to increase in the hour before take off, making it unlikely to be the pre-flight signal.
Instead, Seeley posits that this shaking signal is used to generally rouse the resting bees, making them more aware of activity within the swarm, such as dancing, piping, etc. Much like a ‘pay attention!’ shoulder shake to ensure that the bees are aware of the decision-making process.
To prove causation between piping and swarm warming, Seeley and Jurgen needed to conduct an experiment where they could manipulate the piping signal of a swarm, and then look for and record an effect on swarm warming.
They could do this through artificially “blasting swarm bees with the piping sound” (Pg.161), or artificially blocking them from receiving the signal. They chose the latter method.
To do this, they mounted a 25 x 20cm (10 x 8in) screen vertically over a swarm’s surface so that the outer layer of bees in the cluster were on the other side of the screen. On this screen, they mounted 2 small cages, each of which contained a temperature probe. Soon, these cages were filled with mantle bees.
One cage was closed with a screen cover as soon as piping was heard, thus preventing piping bees from contacting the bees inside the cage.
The other cage was closed with a cover that contained an opening through which the piping bees could pass.
If their hypothesis was correct, and piping bees do indeed stimulate other bees to warm up in preparation for flight, then they should find that the mantle bees in the fully closed cage would not warm themselves before take off; whereas the bees in the open cage would do so. And that’s exactly what happened!
The open-cage bees had a dramatic increase in temperature to 35C/95F in the last few minutes before take off, whereas the closed-cage bees did not. In fact, when Seeley opened the closed cage, the bees seemed “eerily calm” and, when gently prodded, they fell to the ground, too cold to fly
It was clear that these bees had missed the signal to warm up in preparation for flight
Boisterous Buzz-Runners
Now that we know that the piping of scout bees signals the swarm to begin warming their flight muscles, we can turn our attention to what ultimately signals and triggers some 10K bees to take flight in one synchronized movement.
Previously, we saw Martin Lindauer refer to ‘buzz-runners’ (or Schwirrlauf in German). These are bees that run across the swarm cluster with outspread wings buzzing furiously. These active bees will run over inactive bees or through them, knocking them apart, buzzing persistently all the while.
Lindauer noticed that these bees were active in the few minutes before take off, and he theorized that this was part of initiating a simultaneous flight from all the bees in the swarm
Lindauer never tested this theory and, and looking at the data available, Seeley had 3 questions: “What is the interplay between worker piping and buzz-running as a swarm prepares for and then takes flight? Which bees in a swarm perform buzz-runs? And how do buzz-runners know when to produce their rough signal?” Pg.163
In May 2005, Seeley sought answers to these questions and enlisted the help of Clare Rittschof, a Cornell undergraduate student “who turned out to be a born researcher”. Pg.163
Initially, they attempted to ascertain when buzz-runners start their activity. To do this, they mounted a swarm of bees on a vertical board and recorded all activity that occurred with a 10 x 15cm (4 x 6in) area on the swarm
Recording started at the first sound of piping, and ended when the swarm flew off to its new home
Playing back the video recordings in slow motion allowed them to identify any buzz-runners. They also followed each buzz-runner detected with a small microphone to see if these bees were also pipers.
Clare’s careful examination of the data revealed 2 key findings: she saw that more and more bees engage in buzz-running in the hour just prior to take off, until the swarm is teeming with actively running bees. She also identified that all buzz-runners produce audio signals, whether pipes or buzzes, or both.
At first, the running bees were piping but eventually they would combine piping with buzz-running. In fact, during the 5 minutes prior to take off, more than 80% of the running bees produced buzz-runs.
This means that buzz-runners are the very same bees as the pipers, which in turn are the scout bees. This indicates that the scout bees give the piping signals to warm the bees in preparation for flight and then buzz-run signal to trigger flight.
The evidence for this is the fact that the buzz-runner is seen in only one circumstance, when idle bees are being stimulated to fly. Buzz-runners are seen just before the swarm leaves the parent-hive, and then again when the swarm leaves its intermediary resting site towards its newly chosen home.
Buzz-running activity also rises to a crescendo just before take off, with the bees of the swarm becoming more dispersed and active due to the barging through of these runners.
Interestingly, buzz-runners will sometimes fly around the swarm cluster for a few seconds before landing and resuming her buzz-running. To Seeley, this indicates that “the buzz-run signal is a ritualized form of a bee’s take off behaviour, which consists of a bee spreading her wings, starting to buzz them, pushing clear of other bees if need be, and finally taking to the air.” Pg.165
Ritualization: a biology term for the process where an incidental action evolves over time into an intentional signal.
The buzz-run is a good example of this process; a bee about to take flight buzzes her wings so this is a reliable indicator to other bees that she is about to fly. The next step in the signal’s evolution involves the detection of it by others, and how this detection affects their behaviour; specifically, their decision-making. If the signal leads to an improvement in decision making that benefits the signalers and the receivers then the signalers will make the signal even more conspicuous to improve detection by the receivers.
It's likely that early in the evolutionary process, the quiet/resting bees were able to improve their decision making about when to take flight due to the wing buzzing of other bees. Over time, this likely resulted in more coordinated take offs, leading to natural selection favouring the wing-buzz as a signal to other bees.
Looking at the current form of the buzz-run, we can see an exaggerated wing buzz (bigger signal) as well as the actions of running and ramming into groups of quiet bees.
“I think the buzz-run shows nicely how sometimes we can glimpse the evolutionary origins of the marvelous signals that bind bee to bee to bee in a swarm.” Pg.166
When examining the buzz-run mechanism, Seeley has one more key question: why did honeybee swarms evolve this signaling system? Why should the scout bees signal to the swarm when to launch into flight?
Seeley posits that since only the active scouts walking across and through the swarm can sense when all the bees in the cluster are ready for departure (warm enough to fly), the buzz-run signals allows them to transmit this critical information to the swarm as a whole.
We know now that all the 10K+ bees in a swarm must warm their thorax to at least 35C/97F in order to fly. But how can all the bees in a swarm know when all their sisters are hot enough?
If the scouts moving through the swarm are somehow measuring their sisters’ temperatures then they would be able to ascertain when all are ready for flight, and then can signal this to coordinate their take off.
It’s possible that when a scout is performing the run-pause-press maneuver, she is measuring the warmth of the other bee’s thorax.
If scout bees are measuring temps, integrating information received, and then signaling to the swarm to take flight, then honey bee swarms demonstrate a fascinating system of behavioural control within a large group.
“The governance of a honeybee swarm is proving ever more extraordinary.” Pg. 167
Consensus or Quorum?
We have now learned that a swarm starts to switch from making a decision to implementing a decision when scout bees start piping. But how do these pipers know when to begin to pipe? Do they use dancer consensus to know when it is time to begin preparing the others for flight?
This hypothesis would have a scout voting in favour of a site via dance, interacting with other scouts and dancers until they come to agreement on a site, and then somehow this voting is monitored so the scout knows when to begin acting on the decision.
As appealing as this hypothesis is, Seeley notes 2 facts that go against it: firstly, neither Lindauer or Seeley had seen any kind of ‘polling’ behaviour by scouts or dancers. Secondly, Lindauer had witnessed 2 out of 19 swarms that took flight before a consensus was reached.
Can we say that these 2 swarms were mere anomalies that can be dismissed, or do they provide valuable clues into the mechanism behind the decision for a swarm to take flight?
Seeley felt that there was more to these anomalous swarms, and so collaborated once more with Kirk Visscher in an attempt to get to the bottom of this issue.
Visscher shared Seeley’s curiosity as to how scouts in a swarm know when to start piping. They wondered whether the scouts did so by sensing a quorum (sufficient # of scouts) at one of the nest sites, rather than by consensus (agreement of dancing scouts) at the swarm cluster.
The quorum sensing hypothesis postulates that a scout bee ‘votes’ for a site through spending time at it, and we know that the number of scouts rises for a better site, and so somehow the bees monitor their numbers at the site until they perceive that they have reached a threshold number (quorum).
This theory could explain why occasionally swarms take flight without reaching an agreement.
To test this hypothesis, Seeley and Visscher set up an experiment on Appledore Island. First, they presented 4 swarms (one at a time) with 2 identical nest boxes that would be perceived as high quality by the bees, as they wanted to foster strong debate to see if the swarm would take flight before the dancing bees had reached a consensus.
For each trial, the swarm was placed at the center of the island, and the nest boxes were positioned near the shore, both 250 meters/820 feet from the swarm, with one positioned northeast and the other southeast.
In order to view the scout bees inside and outside the nest boxes, each was mounted against a window on the side of a lightproof hut.
Their plan worked and they soon found that scout bees would discover both nest boxes at about the same time. A balanced debate over the 2 sites tended to occur, and the swarms routinely took flight when scout bees were still actively dancing for both sites.
The best example of this was one swarm observed on July 7th 2002. At 12.04pm, both nest sites were being strongly advertised by dozens of bees when the swarm took to the air and then split in two. Each group slowly began to fly towards ‘their’ nest site before returning to the original nest site due to the queen remaining (or returning) there.
This shows that consensus among dancers is not necessary for a swarm to initiate its flight to a new home. But it did offer some support for the quorum hypothesis since it was noted that preparation for flight via piping consistently occurred when 20-30 scout bees were witnessed together at a nest box, with roughly half outside and half inside,
This suggests that 20-30 bees present simultaneously at a nest site is a quorum.
Seeley and Visscher next devised a second experiment to directly test the quorum-sensing hypothesis. One way to accomplish this would be to delay the formation of a quorum at the chosen nest site. This should then delay the beginning of the piping signal and thus the takeoff of the swarm. Nothing else about the decision-making process would be changed.
In order to delay quorum formation, Seeley and Visscher placed 5 desirable nest boxes close to each other at one location on the island. This caused scouts to be dispersed among the 5 nests, instead of concentrated at one. They would then observe how long it took for piping to start at the swarm, followed by flight.
They also conducted a control trial using just one nest box. The two trials (5 boxes vs 1 box) were performed using 2 different locations on the island.
4 swarms were tested and each demonstrated the same behaviour; in the 1 nest box trial, a crowd of bees built up rapidly, whereas the 5 nest box trial had a much slower build up as the scouts were dispersed throughout the boxes.
As a result, with all 4 swarms, there was a delay in piping seen with the 5 nest box trial vs the 1 nest box trial.
The 1 nest box trials had a period of time between piping and flight of 162 and 196 minutes on average, while the 5 nest box trials had a time of 416 and 442 on average.
It is important to note that the amount of waggle dancing at the swarm did not differ between the 2 trials. The level of dance consensus was also the same.
This trial then did successfully disrupt nothing in the decision-making process but the formation of quorum, thus yielding strong support for the quorum-sensing hypothesis.
These 2 experiments led Seeley and Visscher to conclude that a quorum of scouts at a nest site is the key stimulus for scouts to begin piping and thus initiate preparations for swarm flight.
But how to reconcile the quorum-sensing mechanism with the knowledge that a swarm must have reached a consensus among its scouts in order to take off as one cohesive unit to one single nest site?
One possible answer is that the period of time it takes for a swarm to fully prepare for takeoff (usually an hour or more) offers sufficient time for recruitment to the best site to produce unanimous agreement.
Or, perhaps the piping signals inform those scouts advertising a losing site (those without quorum) that the debate is over and they should cease advertising. However, whether this is true is currently unknown. In fact, exactly how scouts reach a quorum remains unknown.
It is possible that they use visual information; witnessing how many bees are inside and outside of a nest site. Or perhaps they use touch, as it has been witnessed that, once a site attracts multiple scouts, they begin to make frequent contact with each other. Are they ‘counting’? Using the rate of contact with other bees to assess the number of fellow scouts at any one time?
It’s also possible that they use scent. Scout bees often fan their wings and expose their scent organs when at a potential nest site. This attracts other scouts to the site, and it is possible that the preceding rise in attraction pheromones indicate to the bees just how many scouts have arrived.
Seeley states that testing these possibilities remain a subject for future study (so stay tuned!)
Why Quorum Sensing?
Knowing that a consensus ultimately needs to be reached in order for a swarm to successfully fly as one to its newly chosen site, why do honeybees rely on quorum-sensing instead of consensus-sensing?
Seeley suggests that consensus-sensing would be extremely difficult for the bees, as this would likely involve each scout needing to travel over the swarm, read dances, and keep a running tally of these readings. This would become increasingly difficult as a swarm increases in size as large swarms would have more scouts and thus more dancers to poll.
In contrast, a quorum size can be fixed; it is not affected by swarm size.
Seeley also suggests that quorum-sensing strikes a balance between speed and accuracy in decision making. Once enough scouts have appeared at one of the sites, take off preparation can begin, even if other scouts are still advertising.
It seems, then, that there is no real need to wait for consensus when the outcome can be sensed in advance via quorum.
Relying solely on consensus would greatly delay the time until takeoff, which would lead to a depletion in their energy reserves (honey). Knowing that swarms rarely take off after 5pm, this delay could cause a swarm to rest overnight, resulting in an even greater energy drain.
Seeley also considers the matter of accuracy. It seems as if the quorum used by bees is 20-30 bees present at the same time at a site, which requires some 75 scout bees supporting this one site (as a scout spends only part of her time at the site and the rest with the swarm).
Using this 20-30 bee quorum appears to ensure accuracy because it guarantees that scouts will not begin piping until a large number of them have examined a site and judged it worthy.
A poor site would not attract a large number of scouts, thus would not reach a quorum, and so this lower quality site is avoided or ruled out.
Even if a single scout were to judge a poor quality site as high quality, when other scouts visit and examine it, they will ‘correct’ her error by refusing to advertise for it,
“I suspect that quorum size is a parameter of the bees’ decision-making process that has been honed over evolutionary time to provide an optimal balance between speed (favoured by a small quorum) and accuracy (favoured by a large quorum). We will examine this matter further in chapter 9.” Pg.174
And that's it for this chapter! Up next is Chapter 8: Steering the Flying Swarm. Please join me in 2 weeks to learn more. We only have a few chapters left of the book now!
In the meantime, I highly recommend looking into bringing ducks to your homestead or farm. I mean, just look at how happy I am to be holding these cuties!