1. Population dynamics

Complex interactions between internal factors (e.g. diseases, beekeeping practices, colony strength, etc.) and external factors (e.g. climate, location, food sources, etc.) influence colony dynamics and growth. Colonies can adapt to environmental challenges to a certain extent, insofar as they adjust the queen’s egg-laying rate, brood development, and individual longevity.

Brood development reaches its peak in June (green line) (► download presentation as a pdf)

The main internal factor driving colony development is the number of eggs laid by the queen. Queens’ egg-laying rates vary among individuals. They depend on genetics and are limited by the queen’s physiology and nutritional status, as well as by the space available in the combs for egg laying. The amount of brood obtained depends on food availability and on the workers’ “diligence in brood care”. Brood survival and worker longevity determine how many eggs develop into functional individuals and thus the colony’s final size. Brood quantity, in turn, depends on climatic conditions and their influence on food availability. Given the very large variability, choosing a suitable apiary site is fundamental—probably even more important than the bees’ genetic inheritance and lineage (Ruttner and Ruttner, 1976).

 

The beekeeper can have a major influence, on the one hand by preventing disease through hygienic working methods, and on the other hand by promoting disease by transferring pathogens from one hive to another. Colony development can also be affected by human-caused poisoning, for example through the improper use of agricultural pesticides or varroacides.

The beekeeper has a major influence on development

 

Bee reproduction occurs through the division of the mother colony. As in other social insects such as most ants, wasps, and termites, only the queen lays eggs and only the queen can found a new colony. In honey bees, however, the queen must be accompanied by a large number of workers in order to form a reproductive unit capable of survival: the swarm.

To maximise the chances of survival of both units—the swarm and the mother colony—it is the old queen that leaves the mother colony to found a new one. The new queen that emerges in the mother colony inherits the security of the old nest and the established foraging area, but also existing brood diseases. She must also perform her mating flight, which exposes her to predators, accidents, and diseases (via drones). When circumstances allow (good nectar and pollen flows), a colony can produce several swarms during the same season.

2. “Swarming fever”: the swarm prepares

If the number of capped cells exceeds the number of uncapped cells, the risk of swarming increases.

When a colony has grown large and the bees have almost no space left available, the queen’s movements also become restricted, especially as there is more and more capped brood and she can hardly find empty cells in which to lay eggs. The Anhardt gland then secretes a marking pheromone (footprint).

This secretion is 10–15 times more abundant in the queen than in workers, but the chemical composition of this pheromone is almost identical between these two castes (as opposed to that of drones, which is very different). As she walks over the frames, the queen deposits this pheromone which, when associated with the deposition of a mandibular pheromone, prevents workers from building queen cells. In the queen, the development of the Anhardt glands and the secretion of the marking pheromone follow the (seasonal) egg-laying rate and decline with the queen’s age. When the area of capped brood is very large and empty cells are lacking, slowing the egg-laying rate, and when the large number of workers pushes the queen to wander on the upper part of the frames, swarm cells appear at the bottom of the frames. The same phenomenon is observed if the beekeeper “cuts the brood in half” by inserting a sheet of foundation. The part of the frame less visited by the queen will soon contain an undesirable queen cell.

The queen then remains mainly in the upper half of the combs and can hardly reach the lower ends. There, queen cells will soon be built. It can be assumed that contact with the queen prevents the construction of queen cells. Indeed, as she walks, she spreads two chemical signals—pheromones—with her tarsi (segments of the feet).

 

The “queen footprint” pheromone (Footprint Pheromone)

Photo: S. Imboden

 

One of these pheromones is produced by the mandibular glands, the other by the tarsal glands. In egg-laying queens, the tarsal glands are particularly well developed. Experiments have shown that a mixture of the two pheromones prevented the formation of queen cells. “Swarming fever” sets in when these pheromones are no longer produced in sufficient quantities or are poorly distributed across the combs.

Workers begin building queen cells along the edges of the brood nest, in which the queen will soon lay eggs. This marks the start of an uninterrupted cascade of events:

• Foraging, the urge to build, and the desire to clean decrease considerably
• Aggressiveness increases
• Workers feed their queen less. They shake her, push her, and even bite her
• As a consequence, the queen loses weight and reduces her egg-laying activity. At the same time, she becomes fit to fly again
• Bees also prepare for “departure” and gorge themselves with food. Within about ten days, the average weight of their honey stomach quadruples. Even bees that will not leave take part in these feeding frenzies
• The sugar concentration of the contents of the workers’ honey stomach increases from about 40% to 70%. Other reserves are accumulated in the bees’ fat body.

Key point Swarming is prepared over 7 to 12 days; it is not sudden.

3. The primary swarm

Under normal conditions, open brood occupies more space than capped brood. A few days before swarming, due to a lack of space for egg laying, but above all due to the slowdown in egg laying, capped brood occupies more space than open brood. It is at the moment when this ratio reverses and the bees cap the first queen cell that swarming fever is triggered.

 

Queen cells at the bottom of the frame often indicate impending swarming

 

Most swarms take off between 11 a.m. and 4 p.m. If swarming is delayed for several days by poor flying conditions, or if it is a secondary swarm, one can hear the young queens “singing” in the queen cells. In that case, the day before the bees depart, the colony is calm. On the day of swarming, and just before departure, the queens press their thorax firmly against the combs to transmit vibrations, which the combs conduct particularly well. Bees perceive this signal via special organs located in their legs. Emerged queens “sing”, while those still in queen cells emit stridulating sounds. In reality, queens do not sing, but do indeed generate vibrations with their wings. If several queens are present in the same colony, each sound elicits a corresponding response from a competitor.

 

The emergence of the first queen often triggers the departure of the swarm

 

The function of these signals has not yet been clarified. They may serve to inform young queens of the presence of competitors and to help them decide within the swarming process.

Workers can also “sing”. Before a swarm leaves the hive or the branch on which it is hanging, a few workers prepare it for take-off by “singing”. They then begin to warm their muscles. Swarm departure is triggered by the same workers that run frantically among their nestmates. They run in zigzags over the combs and vibrate their wings at short intervals. The agitation then spreads like an avalanche throughout the colony. While workers appear idle on the landing board, their wax glands are active and six small wax scales appear on their abdomen (visible by turning the bee over), ready to build new honeycomb in the future hive.

Then a true tide of bees pours out of the entrance, most often carrying the old queen with it. About half of the colony’s population (in the case of a primary swarm) leaves the hive into the open air (about 1,000 bees per minute). Bees from the neighbouring colony may join this cloud of bees.

 

The cloud of a swarm is a spectacular sight

 

When a swarm emerges from a hive, it does not fly directly to its new site. It usually settles in a tree or on a branch a few metres from the original hive (which sometimes allows the beekeeper to recover it if it is noticed in time). Attracted by various chemical signals, the bees form a cluster around the queen and then calm down rapidly. The pheromones from the sting chamber and the queen’s mandibular glands, combined with the fanning scent from the Nasonov gland of the scouts, have an attractive effect. While young bees form loose chains at the centre of the cluster, older workers form a dense mantle around them.

 

The swarm first settles 10 to 50 m from the apiary (which sometimes allows the beekeeper to recover it if it is noticed in time)

But the swarm still lacks suitable housing. About 5% of the swarm’s bees (the most experienced) leave as scouts to search for suitable new sites. This intermediate stop lasts only one to three days. Bee swarming is a genuine process of direct democracy and collective intelligence, as it involves reaching a consensus on the future location of the colony.

All scouts have the same informational power and present their findings transparently and often simultaneously. Depending on the intensity of communication, the bee that has discovered a site recruits a larger or smaller number of additional scouts, each of which visits the site and undertakes an independent assessment. They, in turn, can express their opinion. After several hours—and sometimes up to three days—of continual pooling of knowledge, a consensus emerges from this decision-making process and leads to the final choice of destination. A decision is often reached when around 80% of the scouts agree on one site and/or when there is a quorum of 20 to 30 scouts present at a potential nesting site. As soon as the scouts have agreed on their new quarters, they return to the swarm to indicate the way. They make back-and-forth flights at high speed within the mass of bees in the direction of the new location.

This collective decision-making process succeeds remarkably well in identifying the most suitable new site and keeping the swarm intact.

A good nest should have the following qualities:

• be large enough to accommodate the swarm (minimum 15 litres in volume, preferably ~40 litres),
• be well protected from the elements (not too windy) and receive some warmth from the sun (preferably partial shade and an entrance facing east to benefit from morning warmth),
• have a small entrance (about 12.5 cm2) located at the bottom of the cavity,
• not be infested with ants.

Nesting sites with old bee nests or abandoned hives are preferred, as the smells of honey and propolis reassure scouts (this is used for swarm trapping).

Once the swarm is definitively established, workers rapidly build wax comb for new brood and for storing honey. The queen resumes egg laying only three days after arrival at the new site, to ensure the development of the new colony as quickly as possible.

As the queen can live up to five years, she may swarm several times in her life (although beekeepers generally replace queens every year or every two years to ensure maximum egg laying).

 

Unfortunately, a swarm in the wild does not survive without treatments against Varroa destructor (photo: S. Imboden)

 

If a swarm establishes itself somewhere in the wild, it is said to have returned to a feral state. Unfortunately, the probability of survival beyond two years is low because, with the arrival of the parasite Varroa destructor in the 1980s, diseases are transmitted, leading to colony death.

It is sometimes possible to observe swarms even in September. However, the earlier in the year a swarm sets out, the better its chances of building a population large enough to overwinter and to accumulate sufficient stores for winter.

4. The secondary swarm

The bees remaining in the parent hive have shelter and ample food reserves. However, with the departure of the primary swarm, the size of the mother colony has decreased by a few thousand bees. Although the old queen’s egg laying was greatly reduced just before swarming, brood rearing had previously been in full swing. In the remaining colony, new bees are continually emerging, and the population regains its initial size within a short time.

The first queen to emerge after the departure of the primary swarm, still unmated, frequently leaves after about one week with a secondary swarm, sometimes accompanied by several other young virgin queens. The number of bees in these secondary swarms is most often lower than in the primary swarm, and the new queen is not yet laying. It is therefore not easy for these small swarms to form a colony capable of surviving the winter with sufficient bees and food reserves.

 

There are several types of swarms: Primary swarm: First swarm that leaves with the old queen Secondary/tertiary swarm: Swarm with one or more young unmated queens leaving after the primary swarm. A colony can produce several swarms (tertiary, quaternary, …) Singing swarm: If the old queen in the hive dies before swarming, the young queens sing vigorously in their cells and announce their emergence False swarm: The queen remains in the hive when the swarm departs or returns to it Deceptive swarm: Following a prolonged period of bad weather, a large number of workers may accompany the queen on her mating flight. If the queen falls during mating with a drone, a cluster of bees forms around her and then quickly disperses Hunger swarm: Swarm caused by a long period of famine.

 

There can be only one queen per colony. In the original hive, the first queen usually emerges from her cell about one week after the first swarming. Instinctively, she will want to eliminate the other queens still inside their queen cells; but if the colony is populous enough, it will protect the queen cells and prevent this first queen from killing her sister queens. The first queen will then begin to “sing” to signal her presence. If other queens ready to emerge hear this song, they respond from inside their cells, and if the first queen judges that there are too many rivals to eliminate in order to reign, and too much opposition from the workers, she often decides to leave the hive in a secondary swarm to avoid numerous potential fights (her venom production not being sufficient). The process is repeated with the next virgin (emerging) queen. There can therefore be tertiary swarming in the most populous hives. When the colony is no longer strong enough to oppose the queen, it allows the first emerging queen to kill her sisters by chewing through the side of the queen cells and stinging the pupae within their cells; but if two queens emerge at the same time, a fight to the death ensues, which can injure the survivor and thus produce a poor-quality queen. Conversely, if all goes well, one week later the victorious queen performs her first mating flight (see video below).

Until the first bees of the new generation emerge (about 35 days later), the parent colonies are for the most part considerably weakened and often no longer produce a summer harvest. Nevertheless, they generally manage to reach a sufficient size to overwinter.

5. Risks

Swarming is a vulnerable stage in the life of bees. During this phase, they are supplied only by the nectar or honey they carry in their stomachs. A swarm can starve if it does not quickly find a site to settle and nectar sources. This occurs most often with swarms that leave too early in the season in spring on a warm day that is followed by cold or rainy weather. The original colony, after splitting into one or more swarms, is generally well supplied with food, but the new queen may be lost or eaten by predators during her mating flight; finally, bad weather can prevent her mating flight. In that case, the hive no longer has young brood to rear additional queens and will not survive.

 

A swarm is very impressive, but the danger to humans is lower, because a bee from a swarm rarely stings for several reasons: The bees are homeless, without brood and without stores. They have nothing to defend. Each bee fills its honey stomach with honey before departure. This is the only food source available to the swarm in the short term. A bee gorged with honey does not sting. This is also why we smoke a hive before approaching it: smoke causes bees to gorge on honey in case of an emergency departure due to a fire. The mass sacrifice of bees directly weakens the swarm, since a bee dies after stinging a human (sting torn out). Establishing the new colony requires keeping as many bees as possible.

For humans, the swarm is not dangerous

A beekeeper can therefore approach or touch a swarm with little risk of being stung. However, a calm temperament and very slow movements are required in all handling, in order to allow the bees to take their place without being jostled, and to avoid being associated with danger. It is nevertheless worth knowing that any crushed bee will sting in return, whatever its mood.

6. Recovering swarms

Some beekeepers capture swarms that are reported to them. The advantage is that they gain an additional production swarm for their apiary. The drawback is that they acquire a swarming colony with an unknown queen quality instead of a more stable selected stock. Nor is the health status of the swarm known; it could carry diseases or varroa mites. There are different methods for capturing a swarm. It is a delicate procedure in which the majority of individuals must be secured, with the remainder potentially recovered afterwards.

Collecting a swarm in Montfavet in the 1900s

 

When a swarm settles and forms a cluster, it is relatively easy to capture it in a small hive called a nucleus. One method that can be used on a sunny day, when the swarm is on a lower branch or a small tree, is to place a white sheet under the swarm’s location. A nucleus is placed on the sheet. The swarm is sprayed from the outside with a sugar-water solution (spraying sugar water on swarm bees makes their wings sticky, preventing proper flight: they will remain calmer or will not go very far) and then shaken vigorously off the branch. The main cluster, including the queen, falls onto the white sheet and the bees quickly enter the first dark space they see, which is the nucleus entrance. An organised march toward the entrance follows, and after 15 minutes most of the bees are inside the nucleus. They remain confined there for one or two nights. If the hive is welcoming (cleanliness, location, protection), the swarm will stay.

When recovering a swarm (especially a secondary or tertiary swarm), it is preferable to keep the nucleus cool (so that the swarm tightens around its queen) and in darkness for 48 hours; otherwise, the swarm may easily abscond. Another way to anchor the swarm is to give it a frame of fresh brood. Forty-eight hours after recovery, the new colony is given 50/50 syrup so that it can quickly build the combs of its hive; the bees remain at home to feed it and keep it warm.

 

6.1 Work procedure

• capture the swarm
• keep it for 1–2 days in a cool cellar
• rehouse it in the new hive
• feed it
• check for the presence of queen cells
• it is recommended to treat the swarm with oxalic acid before the brood is capped

Capturing the swarm

• spray water on the cluster forming the swarm
• shake or brush the cluster into a swarm box or into a nucleus with 6 frames of foundation
• place the swarm box or nucleus on the ground nearby (in the shade or cover with a damp cloth)
• leave an opening so that bees still in flight can join the swarm
• only one hour later, or in the evening at dusk, close the swarm box and place it for one or two nights in a dark, cool cellar (feed if necessary)
• rehouse the colony the following evening (primary swarms can also be rehoused immediately) and feed until the frames are built (3 to 8 litres of syrup)
• it is important to treat against varroosis fairly soon after capture (e.g. with oxalic acid, broodless)
• after 12 to 14 days, check for any queen cells, colony strength, frame construction, food stores, and the presence of the queen and egg laying (for secondary swarms, the queen still has to mate, and laying will begin about 2 weeks later)
• expand with frames to be built and feed if necessary

 

Many beekeepers report successful use of a swarm catcher. With this and a bit of luck, recovering a swarm is very simple. As soon as the bees have clustered on the swarm catcher, it can be easily retrieved.

With a swarm catcher and a bit of luck, recovering a swarm is simple.

 

The quality of recovered swarms depends on the time of recovery. Secondary or tertiary swarms in April or May generally pose no problem. Those hived after the end of June will have more difficulty developing. As old beekeepers say: “A May swarm is worth a cartload of wheat! A June swarm is worth a cartload of hay! A July swarm isn’t worth a crumb!”

6.2 Care for colonies that have swarmed (parent colonies)

From day 1 to 5 after the swarm departs, check whether a new queen is present; remove all others or split the entire colony into several nuclei, each with a mature queen cell. If no queen is present, leave only one queen cell. If the young queen emits sounds (queen piping), the colony wants to swarm again. In that case, young queens or queen cells must be removed immediately (they can be used to create nuclei). Only one queen or one queen cell should remain in the parent colony. Depending on the nectar flow or the strength of the colony, remove a few honey frames and tighten the brood nest so that all frames are well occupied. After 14 days, the young queen should be laying. If there is no brood, insert a test frame (queenlessness test).

The queenlessness test

A broodless colony is not necessarily queenless. The queen may be taking a break from laying, or the colony may be undergoing supersedure (natural requeening) and the young queen is not yet laying eggs. Do not forget that a queen may not have been mated.

For a queenlessness test, introduce a frame without bees containing eggs and young brood. If the colony is queenless, three days later you will find emergency queen cells on the test frame.

7. Factors favouring swarming

• race and strain of the colony: some races swarm much more than others
• genetic predisposition of the queen
• time of year: especially in spring before the main honey flow
• lack of space (congestion of the brood chamber): many frames of capped brood, no laying space for the queen, with a very high concentration of bees
• a hive that has become too small: this generally occurs after the arrival of large quantities of pollen, which rapidly increases the colony population. Consequence: a dilution of the concentration of queen pheromones because the colony is too populous
• lack of space to store honey during the honey flow
• lack of space for comb building
• unfavourable weather conditions: prolonged bad weather after a good blossom flow, changeable weather
• too much liquid feeding at the end of spring
• queen age (2 to 3% swarming for a queen in her first year, but n+1 ➜ 20% (for a 2-year-old queen) and n+2 ➜ 50% (for a 3-year-old queen). Destroying queen cells is not sufficient to prevent swarming)
• excessive sunshine on hive entrances and too high a temperature inside the hive (insufficient ventilation)

8. How to control swarming?

• provide space in time (new frames to build, add supers, remove brood frames with bees, etc.)
• allow the building of many foundation frames
• regularly cut out drone comb
• introduce high-quality young queens
• more swarm-prone genetic predisposition: choose a high-quality queen. “Run-of-the-mill” queens swarm much more than queens produced by professionals.
• provide shade on the hive entrance in the afternoon with deciduous trees (plant deciduous trees to create shade…)
• clip one wing of the queen (this is not a method to prevent swarming, but a method to facilitate swarm recovery)
• regularly destroying queen cells (at least once a week) is sometimes recommended, but in fact it tends to accelerate swarming
• remove a package of bees
• remove frames with queen cells and make nuclei; the queen can be replaced later if desired
• remove the queen: take a frame with the queen and move it to a nucleus in a distant apiary; destroy queen cells immediately and again one week later; return the queen to the hive, as if introducing a new queen
• replace the queen: if the queen is replaced and queen cells are removed, swarming fever will likely subside
• splitting or artificial swarming (see chapter 8.1)
• reversing brood boxes in spring (see chapter 8.2)
• apply the Demaree method (or checkerboarding). Its main objective is to separate uncapped brood, including eggs, from the queen (see chapter 8.3)
• apply the virdis method: transfer capped brood into a 2nd brood box above the first (see chapter 8.4)
• caging the queen (method currently being tested by Serge Imboden and Claude Pfefferlé, Société d'apiculture de Sion: www.apision.ch):  See chapter 8.5 and the article: ► Extinguishing swarming fever

 

8.1 Method 1: artificial swarm

(see article : ► Creating young colonies)

Work procedure:

• catch the queen from the parent colony and place her in a queen cage
• place the cage with the parent colony queen or a new reared queen in a swarm box (or in a nucleus with frames of foundation)
• take 1 to 2 kg of bees from the colony (or from several colonies) but without the queen, and brush them into the swarm box
• immediately give a little liquid feed to the artificial swarm
• keep the swarm in a dark, cool cellar until a homogeneous swarm cluster has formed around the queen cage (one to two nights)
• place it at a young-colony site about 3 km away with frames of foundation and release the queen (if the artificial swarm is to be housed at the same site as before, it must be kept at least 4 nights in the cellar and fed)
• first inspection after 7 days (check whether the queen is accepted; otherwise introduce a new queen; number of bees, food, etc.)
• treat the nucleus with oxalic acid (by spraying, trickling, or evaporation)
• check the donor colony (queen cells, presence of the queen, presence of eggs/larvae)

see also:

► Artificial swarm
► Artificial swarm with queen

 

8.2 Method 2: reversing brood boxes

(see also the article: ► Understanding swarming)

An easy method is to reverse brood boxes in spring. It is mainly applied to colonies overwintered on two brood boxes, although it can also be applied—after adding a second brood box—to colonies overwintered on one brood box, outdoors or in a cellar. The principle is as follows:

Bees in hives overwintered outdoors on two brood boxes consume their syrup all winter while gradually moving up to the upper box. Normally, at the end of winter, the cluster is in the upper box, with the lower one empty. The queen therefore begins laying in the upper box. By reversing the boxes at that moment, the empty space is placed above the cluster and brood, which is more natural for the colony. The queen can then move up and lay in this empty box. The boxes can be reversed again a few weeks later, when the brood in the lower box is emerging, in order to place this new free space at the top of the colony. This ensures laying space for the queen and also maximises the number of foragers that will go out when the honey flow arrives.

 

8.3 Method 3: the Demaree method

A good way to prevent swarming is to use the Demaree method. It was devised by George Demaree and first presented in the American Bee Journal in 1884. Its main objective is to separate uncapped brood, including eggs, from the queen. Brood is placed above a queen excluder while the queen is kept below. This reduces hive congestion and the tendency to swarm. It thus allows the entire population to be retained and honey production to be maximised.

This involves creating an artificial swarm without physically splitting the colony. All brood is transferred—except for one good comb with larvae and capped cells—into a brood box placed above the honey supers (for Dadant hives: two supers stacked). In the lower box, one stores frame, the brood comb (with the queen, of course), and eight empty drawn combs are left. The queen excluder is then placed between the lower box and the honey supers.

• The queen is thus left with eight combs in which to lay. Most bees remain above with the brood, but will move down as the brood emerges. They may eventually fill the upper brood box with honey.
• As the bees remaining with the upper brood no longer “sense” the queen (who is below), they will consider themselves queenless and will attempt to rear a new queen from eggs present in the combs. It is therefore important to return and destroy ALL queen cells on the frames of the upper box one week to ten days after the operation.
• This method “makes” the bees believe that swarming has occurred, and in addition, the sudden provision of laying space for the queen will increase colony population noticeably in the following weeks.

This plan is initially intended to reduce or even suppress swarming by separating the queen from almost all of her brood, forcing nurse bees to leave her to care for the nursery separated by an excluder and located at the top. Swarming conditions are therefore no longer met at that moment; it is a swarming within the hive. It is applied to a strong colony, but if the goal is to obtain queen cells, one can work a colony of medium strength. The advantage of this plan, which requires little time to apply, is that the often tedious search for the queen is avoided, the bees retain the same colony odour, and the honey harvest is substantial if weather and floral conditions are favourable. There is no division, no picking.

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See also :

• Understanding swarming
• Queen cells
• Colony splitting
• Pheromones and chemical communication