The Significance of Secondary Swarms and What Science Says

History of Swarming

_{Most beekeepers are quite familiar with swarming. Some dread swarm season and fear for their reputation as a ‘good beekeeper’ if they haven’t managed to control swarming. Swarming or colony fission is a natural reproductive strategy and it was once quite acceptable for beekeepers to let their colonies swarm. In fact, many years ago it was actively encouraged in skep beekeeping because that was how apiaries were stocked since many beekeepers killed off most of their colonies at the end of summer and then needed replacements for the next season. However, commercial beekeeping took off at the beginning of last century in the UK and beekeepers focused on keeping large colonies and manipulating them for maximum honey production. This included controlling honey bee reproduction and preventing swarms which became an essential part of that process. If you look at most of the beekeeping manuals you will find a confusing conglomeration of different ways to prevent swarming and maintain your colonies as one strong unit for honey production. Lots of systems and equipment named after their beekeeper inventors—Pagden, Demaree, Taranov, Horseley, Snelgrove and more. Some methods are very complicated and require so much equipment, and others are quite straightforward and need just a nucleus box for housing a colony’s mother queen and some of the brood and bees.}

My Swarm Season

_{I love swarm season and the excitement of hearing the increasing noise in the apiary as more than half the inhabitants of a colony rush out of their hive with an urgency like it was on fire. With the window open as I wash dishes in the kitchen, I hear the normal apiary comings and goings from the hives on busy days. I can tell when things change and I hear the rising roar and rip off my gloves and rush outside just like the bees. I listen and watch with wonder every time it happens and I just love the swirling clouds of bees that stir the air as they birl round above the apiary before deciding where to settle and bivouac. Not my bivouac lures this year, though you can see one in action above. I experimented with letting the bees deal with swarm season themselves in two colonies. Three colonies out of four swarmed. One of these sent out one secondary swarm, and one sent out two secondary swarms. The third colony sent out a primary swarm and I checked the brood nest a week later to release mature queens from their cells and destroy emergency cells.  I took a couple of mature cells to create nucleus colonies. I know from Ted Hooper’s work that a colony will not send out afterswarms when all the virgins are released at once. Swarming can be over and done within 10 minutes and if you’re not in the apiary at the time you could easily miss them. My BroodMinder temperature sensors confirmed all my swarms. I’m reviewing my experiences this season and planning ahead for next year. This involves talking to friends and delving into the literature.}

What Science Offers

_{I’m glad that modern science is helping us understand the importance of swarming and that the myths associating swarming with ‘bad beekeeping’ are being busted. Dr. Delaplane discusses the benefits of swarming in Honey Bee Social Evolution (1). We learn of mounting evidence that swarming has beneficial health benefits for a colony including lower levels of brood diseases and parasites, lowering nest congestion in the old nest and providing a clean disease-free new cavity. Bees that join a swarm have different age-based and kinship attributes which also contribute to the new colony health and welfare. If you think about it, when the beekeeper makes an artificial swarm, it is done without any knowledge of which bees and which new queen would best serve the new colony.}

_{I discuss swarming in a previous blog https://www.beelistener.co.uk/honey-bees/how-to-get-honey-bees-buying-swarming-bait-hives/ and today I’m focusing on secondary swarms and why they happen.}

Secondary Swarms

_{Secondary swarms are also called afterswarms or cast swarms and they often follow hot on the heels of the primary swarm which usually contains the colony’s mated mother queen. Secondary swarms may contain one or more virgin queens and they are usually considerably smaller than the primary swarm. Beekeepers often wonder why these swarms keep on coming, and it is surprising that a colony will keep on dividing up and sending out such small units of bees some of which have no chance of survival. We will come to that later.}

_{It is worth remembering that a colony starts preparing for reproductive swarming in the dead of winter when the first new eggs are laid after a natural gap in egg laying. In temperate climates that is—in the tropics egg laying doesn’t normally stop. Thermoregulation of the brood nest begins in winter in temperate climates and egg laying increases as winter ends and summer progresses. A colony can contain from between 10, 000 – 60, 000 bees, or more! and a primary swarm usually contains about 60% (2/3) of the adult bees which increases their chance of survival.  Winston’s (2) swarm studies inform a considerable amount of what we know today and he reveals a strong correlation between the area of sealed brood when the primary swarm leaves, and the number of afterswarms. The number of afterswarms sent out depends upon how many workers are needed to stay behind in the colony. One of the Winston study colonies sent out a primary swarm with 14,834 bees. This was followed by 1st afterswarm with 13, 778 bees, 2nd one with 3,765 and 3rd with 4,296. A total of 36,66 bees left this hive. Another colony sent out a primary swarm of 21,000 bees and one afterswarm with 10,608 so a total 32,426 bees left that hive.}

_{Winston (3 ) explains that extensive afterswarming, especially second to fourth afterswarms, does not appear to benefit a colony because these swarms are smaller and issued later which reduces their chances of survival. Swarming in temperate climates usually coincides with good forage availability and nectar flows which are of course both seasonal and variable. Interestingly, colonies send out more afterswarms during good years and in areas with longer growing seasons. Winston says, “In Kansas, for example, colonies produced and average of 2.0 afterswarms during one spring, whereas further north, in British Columbia, colonies produced averages of 1.0 and 1.5 afterswarms two consecutive years….”}

Maladaptive Behaviour

_{Dr Johnson (4) suggests that the production of afterswarms too late in the season may be the result of maladaptive behaviour of bees outside their native range and that there may be a genetic element involved. Studies in France show that the peak in brood rearing which comes before swarming varies between two regions of this country. Colonies that were swapped over between these regions maintained their original pattern of swarming despite the conditions not necessarily being ideal for swarming in their new regions. More evidence for using locally adapted bees.}

How Workers Control Swarming

_{Dr. Seeley (5) explains how workers control swarming and afterswarming. When a primary swarm leaves the hive, the workers can control the emergence of the remaining queens so that they don’t all emerge at once and kill each other. The workers have already decided whether to send out afterswarms based on their sense of brood nest congestion and measurement of colony strength. They can delay the emergence of the next queen till after the current one leaves in a swarm. This is done by not chewing off the strong wax coating and cocoon at the tip of the queen cell to aid her release. They can also reinforce the cell tip with more wax. If there is already an emerged virgin running about, they can keep her away from unopened cells where she might sting the occupant through the cell wall. Amazingly, they can physically hold down two virgin queens and keep them apart till the next queen leaves in the afterswarm. The virgins have no control over what happens next—whether they leave in a secondary swarm or stay home and take over the brood nest of the parent colony. When we see several virgin queens in an afterswarm this is usually because swarming is a chaotic time inside a hive and the workers are not always able to control all emergences amid the jostling and rushing that goes on.}

_{Seeley also discusses a probable kinship factor in the makeup of swarms. It seems that there is a moderate tendency for colonies to divide up into family groups for swarming.  Workers are more likely to leave in a swarm if they are more closely related to the future offspring of the queen. So, a worker has to decide whether to stay and help a half-sister queen, or leave with a swarmed headed up by a full-sister queen.}

Queen Elimination

_{Now we know that workers control the afterswarms and regulate the numbers sent out, but why does a colony send out such small afterswarms that will not survive? Gilly and Tarpy (6) explain that secondary swarms are very costly compared with inheriting the brood nest and they regard them as mechanisms of the queen elimination process. Essentially swarming has two stages which are queen rearing and queen elimination. On average, 15-20 queen are raised to adulthood and the excess are eliminated by other queens before emergence. The workers may facilitate this by opening a cell but not actually killing a virgin queen. The emerged queen locates and kills a rival in her cell by stinging her through the cell wall, or the queens leave in afterswarms and are thus eliminated from the hive.}

Future Plans

_{What have I learned to inform future management? Natural primary swarming allows the bees to determine swarm composition in terms of age, relatedness and usefulness of the workforce, and it fulfils their reproductive urge and need. I’ve certainly seen varroa levels drop way down in the colony that sent out two secondary swarms which has created a long brood break. However, at the moment my plan is to let them send out the primary swarm but not deplete the colony by sending out secondary swarms because the season is so short and weather so unpredictable here and I want the colony to start making plenty winter bees from July onwards and have plenty honey stores for winter. I shall probably use a tip from Alan Baxter and keep a few queen cells in an egg incubator then let them mate from one of my small Apidaea mating boxes.}

References

1)_{Delaplane, K.S., 2024. Honey Bee Social Evolution: group formation, behavior, and preeiminence. John Hopkins University Press.}

_{2) Winston, M.L. Swarming, afterswarming, and reproductive rate of unmanaged honeybee colonies (Apis mellifera). Ins. Soc 27, 391–398 (1980). https://doi.org/10.1007/BF02223731}

_{3) Winston, M.L., 1987. The Biology of the Honey Bee, Harvard University Press.}

_{4) Johnson, B.R., 2023. Honey Bee Biology, Princeton University Press.}

5)_{Seeley, T.D., 1985. Honeybee Ecology: A Study of Adaption in Social Life, Princeton University Press}

6) _{Gilley, D.C. and Tarpy, D.R., 2005. Three mechanisms of queen elimination in swarming honey bee colonies. Apidologie, 36(3), pp.461-474.}