Amazing Swarms

Most often, what you see, if you’re lucky enough to see it at all, is just the high point of the drama:  thousands of bees suddenly pouring out of your hive like a genie from a magic lamp…..and moments later, a buzzing blur that whirls off in some direction and which seems to disappear almost as quickly into a tree or  shrubbery without a trace, if you look away for a tick too long.

If you can locate the concentrated cluster where it has made its bivouac, you might successfully retrieve it into a basket or box….but it sometimes happens that while you are organizing your tools for action,  the swarm unpacks itself and   swirls away before you can say “Apis mellifera.”

How does this “magical” process happen?

Pioneering studies of various aspects of swarming  were conducted by Martin Landauer in the 1950s and were followed up in later decades by many years of experimentation by Thomas Seeley and others.  Although their work has not yet revealed all the secrets, it has elucidated an astonishing level of detail, which Seeley presents in accessible form in his excellent books, scientific publications, and videos.1 

WHY SWARM?  When the hive does not contain sufficient space for the queen to lay the necessary number of eggs (1000-2000/day),  and when there are high numbers of immature bees in the hive and plentiful forage in the surroundings, it is time to swarm.

PREPARATION. Rearing Queens. The process begins when the workers build queen cups along the lower edges of the brood comb. The goal is to produce at least 10 new virgin queens. 

The queen lays a fertilized egg in each cup, or the nurse bees can select and move eggs into cups, if  necessary, and these cups are then “charged” with royal jelly.  They are enlarged as the queen larvae grow, eventually appearing as peanut-shaped swarm cells clustered like fringe along the frame-bottom by the time the larval queens pupate.

It takes 16 days for a new queen to develop from egg to emergent adult.

Shaking the queen (image: TD Seeley)

Slimming the Queen.  Preparing the old queen for flight calls for her to lose 25% of her body weight and to slow and finally stop her egg-laying routine. Workers make these things happen by enforcing the most basic weight-loss method, effective for humans and insects alike: feeding her less while actively pushing her to exercise. They shake, shove, and bite her in a rough manner every few seconds to keep her walking around the nest in a rigorous exercise program until she is fit to fly.2

Fattening up Workers.  At the same time, most of the workers that will be leaving the hive with the swarm stuff themselves with honey, filling their honey crops so completely that their weight increases by about 50%.  In fact, one third of the full weight of the swarm will be from the honey carried by workers to transfer into a new nest!  

Wax production (video image: Butts Bees)

Along with their honey intake, these workers undergo a hyper-activation of their wax glands in preparation for the massive comb-building task ahead.  It’s no surprise that these rather bloated bees become inactive, lingering around the hive entrance without much movement.

Sending out Scouts.  While all this slimming and stuffing, exercising and lounging are going on in the home-hive, a few dozen scouts fly out to seek possible nests within about a 3-mile radius.

Honey bee nest opening in a tall, hollow oak

They visit prospective sites, carefully examining important features. If the swarm-genie could grant itself a wish, the ideal nest would be a high up (at least 15 feet, out of a bear’s reach), south- or north-facing cavity with a small, <2-square-inch entrance at its lower end. 

A volume of about 10.5 gallons would be perfect—somehow estimated from the dimensions in bee-lengths, as scouts measure the interior spaces. The specific volume seems more important than the shape. (Note: a 10-frame deep hive body is about 11 gallons.)

 It can be wet or dry, drafty or not. Both of these features can be corrected by a good sturdy coating of propolis on the entire interior surface and inside the entry to ensure a moisture-free, weather-tight abode.

Sealed swarm cells

DEPARTURE.  Scouts are the organizers and instigators of what will be an EXPLOSIVE departure of the swarm when they determine that conditions outside are appropriately sunny, warm, and calm for travel, at the same time as the new queens have reached the pupal stage and most are sealed into their swarm cells.

Rousing the workersStarting at the hive entrance, each scout rushes around through the crowds of lounging workers, pushing, butting, and prodding, and stopping to press tightly against one after another of her calm, honey-laden nestmates and vibrating her wing muscles at flight speed (~200 cycles per second) for just about 1 second at a time. 

This brief, intensive, thorax-to-thorax vibration makes a buzzing sound called “worker piping” and conveys a clear message:  “Time to Warm Up!” 

That is, it’s time to be ready to take off and fly at a high speed, meaning that workers must warm up their flight muscles to 95ᵒF by vibrating them while keeping the wings themselves at rest. (This is also how “heater bees” generate heat to maintain a high temperature in active brood comb and to heat a winter cluster).

With a ripple-effect, the piping sound is amplified as more and more scouts join in to activate the rest of the workers…and when all are ready for flight (when they’re “piping hot”), the scouts get busy with the second stage of revving up:  the buzz run.

“TIME TO GO!” In the buzz run, each scout zips in zig-zagging sprints through clumps of warmed-up bees that are still lethargic. She buzzes her wings in short flight-like bursts and wiggles her abdomen energetically, head-butting  any laggards (photo to left: “S” marks the scout) and rousing nestmates to join her excited dashes. They quickly engage all the workers in running around and crowding toward the hive entrance.3

All at once, they’re off!!!  They push the old queen out the door along with the crowd as they exit en masse, thousands of bees zooming out to rise in a swirling cloud of maybe 10,000 total, spreading to 30 to 60 feet across, with the queen at the center.2

Scouts fanning “come here”scent at bivouac point (Image: NW New Jersey Beekeepers)

FIRST STOP: BIVOUAC. They don’t go far.  A hundred feet or so is typical before a few scouts settle on a branch or trunk and quickly call in the rest of the crew by releasing and fanning their lemony-scented attractant, enhanced by queen pheromone as soon as Her Highness lands.4

Within minutes, the cloud has condensed to a tight cluster of bees in a ball or elongated shape and remains quiet, calm, and still while scouts exit to search the area for nest site options.

TAKING A VOTE.   Likely no single site is perfect. How do the bees choose?  By voting with their feet, of course! That is, by DANCING!

More on that in a moment—first, a note about the scouts: they are among the oldest and most experienced foragers. About 300 to 500 of them will ultimately go forth to continue the house-hunting that had begun on a smaller scale even before the original swarm departure was initiated. 

Now in earnest, these site-seekers scour an area of several square miles around the swarm cluster, checking every possibility. Some find nothing suitable; others discover acceptable prospects. Many will gather at the most fortuitous locations and try to attract others by animated, energetic waggle dancing on the spot.

A lot of the process of choosing the best site is accomplished by this activity at the various locations being considered, with much shifting and reshuffling of opinion. But in the end, the most critical group to persuade is the swarm itself back at the bivouac—these are the honey-filled workers eager to resettle, build comb, and unload their burdens.

Waggle dance (Image B. Cornissen)

Scouts make many return trips to the swarm, and each time, they perform waggle dances just like those that nectar and pollen foragers do to recruit their nestmates. Each scout’s enthusiasm for a potential home site is expressed by the vigor and duration of her dancing—that is, the number of repetitions (circuits) and the total time of performance.  If the dancer’s excitement inspires her swarm-sisters, they will join an dance along with her as fans of the particular site she is advertising.    

In his experiments, Seeley found that for a site of highest quality, a scout’s dance would be very strong, consisting of over 100 circuits for about 200 seconds total duration, whereas an acceptable, but poorer or mediocre site might be represented by only a dozen brief repetitions.

The ebb and flow of scouts and dancers in this marathon event can actually continue for hours as loyalties and preferences of both scouts and cluster-bees change when they are influenced one way or another by the power of the rival waggle dances.  But at some point, recruitment for all but one site has somehow “melted away,”5 and all the bees on the cluster are doing the same dance.  The decision has been made! 

Evaluating the decision. Seeley found that it is not completely straightforward. For example, part of the decision-making process involves reducing competition from proponents of inferior sites by scouts pushing better ones. They interrupt the rival’s waggle dancing by head-butting her until she exits the competition.6

Swarm cluster  (Image: TD Seeley)2

Seeley concluded after extensive experimenting  and observation that the choice may be reached by attaining a quorum (a sufficient number of supporters), rather than by consensus (full agreement).  Further, the final choice is not made by 100% of the thousands of bees in the swarm; the active participants are the waggle-dancing scouts along with only the swarm bees on the cluster’s surface, which together make up a small percentage of the whole.  

And yet, based on his studies, Seeley demonstrated that the honeybees’ method that has evolved over time ultimately works:  the swarm generally makes good decisions that are also the best compromise between the need to choose SWIFTLY (while a cluster is dangling in the breeze, “holding its breath,” so to speak), and the need to choose WELL (for survival!).2,5

ONWARD TO THE NEW HOME.  The final chapter of this fantastic story describes how the swarm cluster must be reactivated and warmed up again to fly after its long quiescent pause. It then has to be launched into flight and guided to the place they have chosen as their new nesting cavity that none but the scouts have seen.

As in the initial flight from the old hive, the scouts are the literal movers and shakers that initiate the swarm’s synchronized and nearly instantaneous takeoff from the bivouac, and then lead them in a coherent way directly to their new dwelling, with a graceful landing and entry as the finale.

In the swarm cluster, thousands of bees are snugly packed into the interior, but with adjustable air channels for ventilation and heating.  This ball of bees is surrounded by a continuous, dense mantle several workers deep on the outside. The core is maintained close to 95ᵒF, whereas the mantle, which is exposed to ambient temperature, is much cooler.

Nonetheless, these outside bees must keep themselves somewhat warm, maintaining at least a temperature of 63ᵒF even if the air is colder. If their bodies cooled to below 59ᵒ, they would enter a “chill torpor” and could easily fall off of the cluster, unable to fly or save themselves.7  Therefore, in the brief time before the swarm can take off, the mantle bees have to heat themselves to the same temperature as bees at the central core.

Once again, the scouts begin their task of stirring up the swarm bees, starting an hour or so before departure with the first worker-piping vibrations, and shaking, jostling, pushing, and running among the indolent crowds of bees:  “Time to Warm Up!”

Scouts repeat their buzz running activity to let the mantle bees know that it’s time to take off (CC Rittschoff & TD Seeley)3

Once the mantle bees are warmed nearly to the point for flight, meaning that the interior bees throughout the swarm are also up to temperature, the second stage—buzz running—gets going even more energetically than was seen in the original swarm preparation, with similar prodding, butting, zig-zag running, and wing-buzzing, the last of which in this case elevates excitedly to short flights over the backs of the mantle bees, as well.

During the final 10 minutes, the mantle bees heat up exponentially, so that 100% of them have attained a temperature of at least 95ᵒ by the moment of the swarm’s take-off.2  Astonishing that at that point, it takes only 60 seconds for the whole condensed mass to disintegrate and explode to a cyclone of buzzing swarmers that circles for half a minute before taking off in a specific direction, accelerating rapidly and vanishing from view.

 The swarm continues on its way, moving in the big cloud formation with a low density of under 40 bees per cubic yard.  How do they know the direction to fly, when fewer than than 5% of the bees in the swarm had previously visited the new site?2 

Schematic of streaker bees in a swarm [long “velocity vector” arrows], found mainly at the top of the swarm cloud. Only a small fraction of bees in the swarm are shown in this graphic [short arrows] (image: TD Seeley)2

Already in 1955, Martin Lindauer had hypothesized based on his observations that the several hundred scouts act as “streaker bees,” continuously repeating a pattern of zooming at top speed to the front of the swarm cloud in exactly the direction of the new nest, then slowly drifting back along the outside edges before streaking forward again.  Meanwhile, the swarm keeps moving at a moderate pace, competently guided by these fast-flying vectors. 

Tested by Seeley against competing hypotheses that invoked either olfactory or visual cues, the streaker bees scenario was shown to be correct.

And the elegant finishing touch to this flight is that cloud approaches its destination, the guides cause it to gradually slow down through the final 100 yards, then to come to full stop a short distance from the site. Scouts quickly position themselves at the nest cavity’s entrance and fan their Nasanov gland pheromones to call the others to “come here!”

Within 10 minutes, the entire swarm will be tucked safely inside and likely starting right away to set up housekeeping—as cozy, dry, and safe as a genie in a magic lamp.

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