If you have been a beekeeper for even a couple of seasons you will recognize swarming is a frequent topic discussed in the bee magazines. Much has been written about swarming. Despite all the information, swarming remains one of the big challenges to beekeepers.
Swarming means different things to different people. L.L. Langstroth called swarming a “most beautiful sight.” The general public often finds a swarm a terrifying sight. For beekeepers, swarms represent potential new colonies. In our culture of bees, swarms at one time were welcomed as a means to replace harvested hives. Today they can be considered a means of natural mite control by the bees and also a return to more “natural” beekeeping.
The appearance of a bee swarm has been expressed in history as a portent of both good and bad news. Bees that swarm excessively, such as the Africanized bees, represent a stinging hazard to be avoided by the general public and individuals far from medical assistance. Such swarms on the other hand however are a valuable resource for rural subsistence farmers, who capture swarms, or note where swarms establish nests, to return later to rob honey.
Bee swarms have halted airplane departures and auto traffic, delayed sporting events, and terrorized the United States in the book and movie “The Swarm” (1978). Although misunderstood, swarms are only temporary, usually gentle, and not a threat if simply left alone, even in the defensive Africanized bee.
Replacing the colony queen
Bee colonies normally have a single queen with lots of worker bees to do all the work. With just one female reproductive in a bee colony, there is a special procedure to replace the mated queen when it becomes necessary. Replacement of a queen by another queen is a process termed supersedure. Replacement of the queen with colony division and creation of another colony is swarming. The behaviors start similarly but their outcome is quite different.
A third means of replacing a queen, emergency queen rearing, is practiced if the queen dies suddenly, is removed by a beekeeper or is somehow injured or lost from her colony (such as being dropped from a frame being examined). More directly, beekeepers rear replacement queens under emergency conditions. The best reared queens, whatever the process, swarm less even in colonies with a densely crowded population in the brood-rearing area and colony conditions of food abundance, both as stored reserves and daily availability to foragers (or for colonies being fed by the beekeeper).
Note: Wyatt Mangum in December’s American Bee Journal suggests a fourth method of replacement of a colony queen via the process of usurpation. More common in Africanized bees, he has documented it in his Virginia apiary. Thelytoky, as seen most commonly in Cape honey bee. populations, could be listed as a fifth, albeit uncommon, method as well.
Communication of swarming
Each worker bee needs to receive a certain level of queen substance. This social cohesive pheromone is distributed through food transmission. We might consider queen failure as a reduction in egg laying but queen inadequacy is apparently measured by the workers through chemical pheromones. Worker bees become restless in as little as one hour after removal of their queen. Replacement behaviors are seen within four hours.
A failing queen may be unable to produce sufficient amounts of queen substance or the pheromone is not distributed to enough workers. Either condition results in too little of the pheromone being fed back to the queen by the bees of her retinue. This feedback system of queen pheromone distribution is a vital communication that begins the behavior of swarming and supersedure.
The first behavior change observable to the beekeeper is the laying of a fertilized egg in a queen cup. .Queen cups are special cup-like, vertically-opening beeswax precursors of queen cells. They are always present in a bee colony, though their numbers are greatest, and the workers maintain them in prime condition, in the spring months. If queen cups are removed, bees replace them more quickly during the spring than at other times of the year.
Queen cups are often lighter in color than surrounding drawn comb, indicating new beeswax is used to build them. They are normally built at the lower margin of beeswax comb along the bottom bar of frames in a beekeeper’s hive, or in spaces where the beeswax comb terminates, as when comb is damaged.
The queen herself places a fertilized egg in a queen cup. Worker bees can remove eggs from queen cups (as well as from horizontal worker and drone cells). It is controversial as to whether workers can transfer eggs into queen cups or transfer eggs from one worker cell to another. Workers regularly cannibalize eggs laid by the queen.
The vertical orientation of a queen cell stimulates the bees to feed royal jelly to the larva that develops from the fertilized egg. The larva is in no danger of falling out as surface tension of the royal jelly holds it in place. Queens can, in fact, develop normally in a horizontal orientation (or workers in a vertical position) if experimentally reared outside a colony. Orientation is yet another of the critical communications in the dark, smelly beehive.
An occupied queen cup is called a queen cell. Queen cells are repeatedly aborted in a bee colony. Many more cells are started than are successfully completed. Why eggs might be removed from cups once laid by the queen is unknown. Once developed and the cell is elongated into the more familiar-appearing queen cell, the chances of cell abortion are reduced. By chewing a hole in the side of the cell, and perhaps stinging the occupant of the cell, the queen causes the workers to remove a developing queen pupa. Why bees start and then stop raising queens and the extent of such behavior is not known.
Swarming begins with communication. Bees prepare to leave and scouts look for a new home before we are able to detect their preparations. The final result, bees clustered at a bivouac, is called the swarm ; the behaviors of preparation and final departure are termed swarming.
The first swarm is termed the prime swarm. A swarming colony may produce more than one swarm. The others are termed afterswarms. Sometimes, despite all the preparations, swarming is not successful and the departed population returns, often to try to swarm again. Eventually the swarming colony stops rearing queens, one virgin queen becomes the monarch and the swarming colony returns to a normal queenright existence.
A swarm issuing from a hive contains 41-80% of the adult workers of the swarming colony (average 66%). The first swarm to leave (primary swarm) usually contains only the old mated queen but it may also contain virgin queens if weather conditions delay initial swarm departure. Afterswarms often contain several virgin queens (up to 20 in one instance) with fewer worker bees. Virgins coexist in afterswarms without fighting, until they reach their new homesite, when they almost immediately fight until one remains.
Swarms as small as 2,400 bees to as large as 41,000 individuals have been reported. Mean populations were 11,800 bees in one study and calculated at 14,000 bees in another.
Events leading to swarming
Swarming is not a random happenstance. It is difficult but possible to observe and measure some of the events that occur before the bees depart their colony. We assume that swarming preparations begin when the queen lays fertilized eggs in the vertically-oriented queen cups. However, this change in the queen’s behavior is done only in response to stimuli. Factors we can observe include presence of drones, a growing colony and resources being brought in. The queen lays eggs in queen cups over more than one day, selecting queen cups scattered at various locations in the brood area.
Worker bees do not ‘”force” the queen to lay eggs in cups, nor do they later protect the queen cells from her destruction. As in supersedure, the same egg-laying queen can return later to developing queen cells to halt queen rearing.
As queen cells develop, it is possible to observe several additional events in preparation for swarming. The queen begins to lose weight in her abdomen. Workers begin to treat the queen more roughly, including the behavior of vibrating the queen. A queen needs to lose one-third to as much as half of her body weight if she is going to be successful in departing in the swarm. The queen continues egg-laying behavior but at a reduced rate during her forced weight loss, which sometimes is evident by carefully looking in the brood frames.
Worker bees meanwhile are gaining weight because they tend to gorge with honey when preparing to swarm. This behavior starts up to ten days before the swarm issues. Engorgement helps ensure a food reserve for the swarm in transit to a new home since there is little foraging by the bees from the cluster location. As swarming day comes closer, scout bees begin to leave the parent colony to scout for a new nest site.
There is a definite spring seasonality to swarming based on local environment conditions. The vast majority (~75%) of colonies swarm within a six-week period of time in mid-spring. Swarms usually emerge in the middle of the day (10 a.m. to 2 p.m.) on days suitable for flight. Emergence may appear to occur in waves but if you check weather data you will likely see a period of cold, windy, rainy weather without emergence and then a number of swarms emerging once the weather returns to dry, sunny days. Swarms may leave as soon as developing queen cells are capped but usually the primary swarm leaves a day or so ahead of virgin queen emergence.
The process of leaving home is rapid, lasting only 10-15 minutes from emergence to when the bee swarm is fully clustered at a temporary bivouac site. Prior to emergence, bees become quiet in the hive and foraging is reduced. The signal to leave is the buzz run or breaking dance. The queen, who by this time has lost considerable weight, may be pushed toward the entrance by her worker bees.
There is no apparent determination of which bees will exit with a swarm or of those that will stay. Bees of all ages join a swarm. The leaving bees pile out the entrance and join in a circular flight motion, keeping this formation as they move away from the parent hive.
The majority of swarms cluster within three meters (ten feet) of the ground; a few cluster on the ground itself while others may form at higher locations. Those that go to the highest cluster sites are most often the ….