1. Population Dynamics

Complex interactions between internal factors (e.g. diseases, beekeeping practice, colony strength, etc.) and external factors (e.g. climate, location, food sources, etc.) influence the dynamics and growth of colonies. Colonies can adapt to a certain degree to environmental challenges by adjusting the queen's egg laying rate, brood development and the longevity of individuals.

Brood development peaks in June (green line) (► download presentation as PDF)

The principal internal factor in colony development is the number of eggs laid by the queen. The egg laying rate varies from queen to queen. It depends on genetics and is limited by the physiology and nutritional state of the queen, as well as by the space available in the combs for egg laying. The quantity of brood obtained depends on food availability and the workers' diligence in brood care. The survival of the brood and the longevity of the workers determine the number of eggs that develop into functional individuals and the final colony strength. The quantity of brood, in turn, depends on climatic conditions and their influence on food availability. Since variations are very large, the choice of the right apiary site is fundamental – probably even more important than the genetic heritage of the bees and their breeding stock (Ruttner and Ruttner, 1976).

 

The beekeeper can exert great influence, on the one hand through disease prevention by means of hygienic working methods, and on the other hand by inadvertently promoting disease by transferring pathogens from one hive to another. Colony development can also be affected by human-induced poisoning, for example through non-compliant use of agricultural pesticides or varroacides.

The beekeeper has great influence on colony development

 

The multiplication of bees occurs through division of the parent colony. As with other social insects that form colonies – including most ants, wasps and termites – only the queen lays eggs and only the queen can found a new colony. In honey bees, the queen must be accompanied by a large number of workers in order to form a viable reproductive unit: the swarm.

In order to maximise the survival chances of both units – the swarm as well as the parent colony – it is the old queen who leaves the parent colony to found a new one. The new queen that emerges in the parent colony takes over the security of the established nest and the proven foraging area, but also the existing brood diseases. She must also complete her mating flight, which exposes her to predators, accidents and diseases (via the drones). When circumstances permit (good nectar and pollen flows), a colony can form several swarms in a single season.

2. The Swarming Impulse: the swarm prepares

When the number of capped cells exceeds the number of open cells, the swarming risk increases.

When a colony has grown considerably and the bees have almost no space available, the queen's movements are also restricted, particularly when there is an increasing amount of capped brood and she can barely find empty cells in which to lay her eggs. The Arnhardt gland then secretes a marking pheromone (footprint pheromone).

This secretion is 10–15 times more abundant in the queen than in the workers, but the chemical composition of this pheromone is almost identical between these two castes (as opposed to that of the drones, which is very different). As the queen walks across the combs, she deposits this pheromone which, when associated with the deposition of a mandibular gland pheromone, prevents the workers from building queen cells. In the queen, the development of the Arnhardt 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, empty cells are lacking – thereby slowing the egg laying rate – and the large number of workers pushes the queen to move about in the upper part of the combs, swarming cells appear at the bottom of the frames. The same phenomenon is observed if the beekeeper "divides" the brood by inserting a sheet of foundation. The part of the frame less frequented by the queen will soon contain an unwanted queen cell.

The queen then remains primarily in the upper half of the combs and can barely reach the lower extremities. Queen cells will soon be built there. It can be assumed that it is physical contact with the queen that prevents the construction of queen cells. Indeed, she spreads two chemical signals – pheromones – with her tarsi (foot segments) during her movements.

 

The queen's footprint pheromone (Footprint Pheromone)

Photo: S. Imboden

 

One of these pheromones is produced by the mandibular glands, the other by the tarsal glands. In laying queens, the tarsal glands are particularly well developed. Experiments have demonstrated that a mixture of both pheromones prevented the formation of queen cells. The swarming impulse is established when these pheromones are no longer produced in sufficient quantity or are poorly distributed across the combs.

The workers begin to build queen cells at the edges of the brood nest, into which the queen will rapidly lay eggs. This marks the beginning of an uninterrupted cascade of events:

• Foraging activity, comb-building drive and grooming behaviour decrease considerably
• Aggressiveness increases
• Workers feed their queen less. They shake, push and even bite her
• As a consequence, the queen loses weight and reduces her egg laying activity. At the same time, however, she regains the ability to fly
• The bees also prepare for "departure" and gorge themselves on food. Over approximately ten days, the average weight of their honey stomach quadruples. Even bees that will not depart participate in these feeding bouts
• The sugar concentration in the workers' honey stomach contents rises from approximately 40% to 70%. Additional reserves are stored in the fat body of the bees.

Note that swarming prepares over 7 to 12 days; it is not a sudden event.

3. The Primary Swarm

Under normal conditions, open brood occupies more space than capped brood. A few days before swarming, due to the lack of space for egg laying, but primarily due to the slowing of egg laying activity, capped brood occupies more space than open brood. It is at the moment when this ratio inverts and the bees cap the first queen cell that the swarming impulse is triggered.

 

Queen cells at the bottom of the frame often signal imminent swarming

 

Most swarms depart between 11:00 and 16:00. If swarming is delayed by several days due to poor flying conditions, or if it is a cast swarm, the young queens can be heard piping in the queen cells. In this case, the colony is calm on the day before the bees depart. On the day of swarming and just before departure, the queens press their thorax firmly against the combs to transmit vibrations that the combs conduct particularly well. The bees perceive this signal through special organs located on their legs. Emerged queens "pipe", while those still inside the queen cells emit stridulating sounds. In reality the queens do not sing but do produce vibrations through their wings. If several queens are present in the same colony, each sound receives a corresponding response from a rival.

 

The emergence of the first queen often triggers swarm departure

 

The function of these signals has not yet been fully elucidated. They may serve to inform the young queens of the presence of rivals and to assist them in reaching a decision in the swarming process.

Workers can also pipe. Before the swarm leaves the hive or the branch on which it is clustered, several workers prepare it for departure with piping. They then begin to warm their flight muscles. Swarm departure is triggered by the same workers, who run frantically among their colony mates. They zigzag across the combs and vibrate their wings at short intervals. The excitement then spreads through the entire colony like an avalanche. While the workers appear idle on the alighting board, their wax glands are active and 6 small wax scales appear on their abdomen (visible when the bee is turned over), ready to build new honeycombs in the future hive.

A true tide of bees then pours through the entrance, carrying the old queen with it in most cases. Approximately half of the colony's bee population (in the case of a primary swarm) leaves the hive into the open air (approx. 1,000 bees per minute). Bees from a neighbouring colony join this swarm cloud.

 

A swarm cloud is a spectacular sight

 

When a bee 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 source hive (which sometimes allows the beekeeper to recover it if spotted in time). Attracted by various chemical signals, the bees form a cluster around the queen and then quickly calm down. It is the pheromones from the queen's sting chamber and mandibular glands, combined with the fanning scent of the scout bees' Nasonov gland, that have an attracting effect. While young bees form loose chains in 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 spotted in time)

However, the swarm still lacks a suitable dwelling. Approximately 5% of the swarm bees (the most experienced) depart as scouts to search for suitable new nest sites. This intermediate stop lasts only one to three days. The swarming of bees is a genuine process of direct democracy and collective intelligence, since it involves reaching a consensus on the future location of the colony.

All scout bees have equal information power and present their discoveries transparently, often simultaneously. Depending on the intensity of communication, a bee that has discovered a site will recruit a greater or smaller number of new scouts, each of whom will visit it and undertake an independent evaluation. They can in turn express their opinion. After several hours, and sometimes up to 3 days of continuous mutual knowledge-sharing, a consensus emerges from this decision-making process and leads to the definitive choice of destination. A decision will often be made when approximately 80% of the scouts have agreed on a single location and/or when there is a quorum of 20 to 30 scouts present at a potential nest site. Once the scouts have agreed on their new quarters, they return to the swarm to indicate the route. They make repeated passes, flying at high speed through the bee mass in the direction of the new location.

This collective decision-making process is remarkably successful at identifying the most suitable new nest site and keeping the swarm intact.

A good nest site must have the following qualities:

• be sufficiently large to accommodate the swarm (minimum 15 litres in volume, preferably approx. 40 litres),
• be well protected from the elements (not too windy) and receive a certain amount of solar warmth (preferably semi-shaded, with the entrance facing East to benefit from morning warmth),
• have a small entrance (approximately 12.5 cm²) located at the base of the cavity,
• not be infested with ants.

Nest sites with abandoned bee nests or hives are preferred, as the scents of honey and propolis reassure the scouts (a fact exploited in swarm trapping).

Once the swarm is definitively settled, the workers very rapidly build honeycombs for the new brood and for honey storage. The queen resumes egg laying only 3 days after arrival at the new site, in order to ensure the development of the new colony as quickly as possible.

Since the queen can live up to 5 years, she may swarm several times during her lifetime (although in practice beekeepers generally replace queens each year or every two years to ensure maximum egg laying activity).

 

Unfortunately a swarm in the wild does not survive without treatment 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 2 years is low, because with the arrival of the parasite Varroa destructor in the 1980s, diseases are transmitted that cause the death of the colony.

It is sometimes possible to observe swarms as late as September. But the earlier in the year a swarm sets out, the better its chances of forming a population large enough to overwinter and accumulate sufficient provisions for winter.

4. The Cast Swarm

The bees remaining in the parent colony have shelter and ample food stores. But with the departure of the primary swarm, the colony strength of the parent colony has decreased by several thousand bees. Although the old queen's egg laying had been greatly reduced just before swarming, brood rearing had previously been in full swing. In the remaining colony, new bees continuously emerge and the population returns to its original size within a short time.

The first queen to emerge after the departure of the primary swarm, still unmated, frequently departs after approximately 1 week with a cast swarm, sometimes accompanied by several other virgin queens. The number of bees in these cast swarms is generally 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 overwintering with sufficient bees and food stores.

 

There are several types of swarms: Primary swarm: The first swarm to depart, with the old queen Cast swarm / tertiary swarm: A swarm with one or more virgin queens departing after the primary swarm. A colony can form several swarms (tertiary, quaternary …) Piping swarm: If the old queen of the hive dies before swarming, the young queens pipe eagerly 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 an extended period of bad weather, a large number of workers may accompany the queen on her mating flight. If the queen falls during mating with the drone, a cluster of bees forms around her, then quickly disperses Hunger swarm: A swarm triggered by a prolonged period of starvation.

 

There can only be one queen per colony. In the parent colony, the first queen emerges from her cell generally one week after the first swarming event. She will instinctively want to eliminate the other queens still housed in their queen cells; but if the colony is sufficiently populous, it will protect the queen cells and prevent this first queen from killing her sister queens. The first queen will then begin to pipe to signal her presence. If other queens ready to emerge hear this piping, they respond from inside their cells; and if the first queen judges that there are too many rivals to eliminate to reign and too much opposition from the workers, she will often decide to leave the hive in a cast swarm to avoid the numerous potential combats (her venom production being insufficient). The process repeats with the next emerging virgin queen. There can therefore be a tertiary swarm in the most populous colonies. When the colony is no longer strong enough to oppose the queen, it allows the first emerging queen to kill her sisters by gnawing laterally into the queen cells and killing the pupae with a sting through the cell wall; but if two queens emerge at the same moment, a fight to the death ensues which may injure the survivor and thus produce a poor-quality queen. If all goes well, one week later the victorious queen undertakes her first mating flight (see video below).

Until the first bees of the new generation emerge (approx. after 35 days), the parent colonies are generally considerably weakened and often no longer produce a summer honey harvest. Nevertheless they generally manage to reach a sufficient colony strength for overwintering.

5. Risks

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

 

A swarm is very impressive, but the danger for humans is limited, because a bee from a swarm rarely stings, for several reasons: The bees are without shelter, without brood and without food stores. They have nothing to defend. Each bee fills its honey stomach with honey before departure. This is the only short-term food source available to the swarm. A bee gorged with honey does not sting. This is also the reason why a hive is smoked before approaching it: smoking prompts the bees to fill up on honey before a potential emergency departure in the event of fire. The large-scale loss of bees directly weakens the swarm, since a bee dies after stinging a human (tearing out of the stinger). Establishing the new colony requires preserving the maximum number of individuals.

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 necessary in all handling, in order to allow the bees to take their place undisturbed and to avoid being associated with a threat. It is nonetheless worth knowing that any bee that is crushed will sting in response, regardless of its temperament.

6. Swarm Collection

Some beekeepers capture swarms reported to them. The advantage is that they gain an additional production colony for their apiary. The disadvantage is that they obtain a swarming colony with a queen of unknown quality instead of a more stable, selected breeding stock. The health status of the swarm is also unknown; it could be a carrier of diseases or varroa. There are various methods for capturing a swarm. It is a delicate procedure in which it is important to secure the majority of individuals, with the remainder being collected afterwards.

Swarm collection in Montfavet in the early 1900s

 

When the swarm settles and forms a cluster, it is relatively easy to capture it in a nucleus box. One method that can be used on a sunny day when the swarm is located on a lower branch or small tree is to place a white sheet on the ground under the swarm. A nucleus box is placed on the sheet. The swarm is sprayed on the outside with a sugar syrup solution (spraying sugar syrup on the swarm bees makes their wings sticky, preventing them from flying properly: they will remain calmer or will not travel far) and then shaken vigorously from the branch. The main group, including the queen, will fall onto the white sheet and the bees will quickly enter the first dark space in sight, which is the opening of the nucleus box. An organised march towards the opening will follow, and after 15 minutes the majority of the bees will be inside the nucleus box. They will remain confined there for one or two nights. If the hive is welcoming (cleanliness, location, protection), the swarm will stay inside.

When collecting a swarm (especially a cast swarm or tertiary swarm), it is better to place the nucleus box in a cool location (so that the swarm clusters tightly around its queen) and in darkness for 48 hours; otherwise the swarm can easily abscond. Another solution to anchor the swarm is to give it a fresh brood frame. 48 hours after collection, the new colony is given a 50/50 syrup so that it can rapidly build the combs of its hive, with the bees remaining in the hive to feed and warm it.

 

6.1 Workflow

• capture the swarm
• place it in a cool cellar for 1–2 days (cellar confinement)
• rehouse it in the new hive
• feed it
• check for queen cells
• it is advisable to treat the swarm with oxalic acid before the brood is capped

Capturing the swarm

• spray the cluster with water
• shake or brush the cluster into the swarm box or into a nucleus box with 6 frames of foundation
• place the swarm box or nucleus box on the ground nearby (in the shade or covered with a damp cloth)
• leave an opening so that bees still in flight can rejoin the swarm
• only one hour later, or in the evening at dusk, close the swarm box and keep it for one or two nights in a dark, cool cellar (feed if necessary)
• rehouse the colony on the following evening (primary swarms can also be rehoused immediately) and feed until the frames are built out (3 to 8 litres of syrup)
• it is important to carry out a varroa treatment as soon as possible after capture (e.g. with oxalic acid, broodless)
• after 12 to 14 days, check for any queen cells, colony strength, comb construction, food stores, and the presence of the queen and of egg laying (for cast swarms, where the queen still needs to be mated, egg laying will begin after approximately 2 weeks)
• expand with frames to be built out and feed if necessary

 

Many beekeepers report successful use of a swarm trap. With it and a little luck, swarm collection becomes very straightforward. Once the bees have settled on the swarm trap, it can easily be retrieved.

With a swarm trap and a little luck, swarm collection is straightforward.

 

The quality of collected swarms depends on the time of collection. Cast swarms or tertiary swarms from April or May generally pose no problems. Those rehoused after the end of June will have greater difficulty developing. As old beekeepers say: "A swarm in May is worth a load of hay! A swarm in June is worth a silver spoon! A swarm in July is not worth a fly!"

6.2 Care of colonies that have swarmed (parent colonies)

On days 1 to 5 after swarm departure, check whether a new queen is present; remove all others, or divide the entire colony into several nucleus colonies each with one mature queen cell. If no queen is present, leave a single queen cell. If the young queen emits sounds (queen piping), the colony wants to swarm again. In this case, young queens or queen cells must be removed immediately (they can be used to create nucleus colonies). Only a single queen or queen cell must remain in the parent colony. Depending on the nectar flow or colony strength, remove some honey frames and condense the brood nest so that all frames are well occupied. After 14 days the young queen must be laying. In the absence of brood, insert a control frame (queenlessness test).

The queenlessness test

A colony without brood is not necessarily queenless. The queen may be taking a laying break, or the colony may be undergoing supersedure (natural requeening) and the young queen is not yet laying eggs. It should not be forgotten that a queen may not have been mated.

As a queenlessness test, a broodless frame with eggs and young brood is introduced. If the colony is queenless, emergency queen cells will be found on the test frame three days later.

7. Factors Favouring Swarming

• Bee race and breeding stock of the colony: some races swarm considerably more than others
• Genetic predisposition of the queen
• Time of year: especially in spring before the main nectar flow
• Lack of space (congestion of the brood box): many frames of capped brood, no opportunity for the queen to lay with an enormous concentration of bees
• A hive that has become too small: this generally occurs after the arrival of large quantities of pollen that rapidly increase the colony's bee population. The consequence: a dilution of the queen's pheromone concentration because the colony is overpopulated
• Lack of space to store honey during the nectar flow
• Lack of space for comb-building activity
• Unfavourable weather conditions: prolonged bad weather after a good blossom honey flow, changeable weather
• Excessive liquid feeding in late spring
• The age of the queen (2 to 3% swarming impulse for a queen in her first year, but n+1 → 20% (for a two-year-old queen) and n+2 → 50% (for a three-year-old queen). Destroying queen cells alone is not sufficient to prevent swarming)
• Excessive sun exposure on the flight sides of hives and excessively high temperature inside the hive (insufficient ventilation)

8. How to control swarming?

• Provide space in time (new frames to be built out, add supers, remove brood frames with bees, etc.)
• Allow extensive building of foundation frames
• Carry out drone brood removal regularly
• Introduce young, quality queens
• Stronger genetic swarming tendency: choose a quality queen. "Chance queens" swarm far more than professionally reared queens.
• Shade the flight side of hives in the afternoon with deciduous trees (plant deciduous trees to provide shade…)
• Clip one wing of the queen (this is not a swarm prevention method, but a method of swarm recovery)
• Regularly destroying queen cells (at least once per week) is sometimes recommended, but in fact tends to accelerate swarming
• Remove a package of bees
• Remove frames with queen cells and create nucleus colonies; the queen can be changed later if desired
• Remove the queen: take a frame with the queen, transport it in a nucleus box to a distant apiary; destroy queen cells immediately and again one week later; reintroduce the queen into the hive as if introducing a new one
• Change the queen: if the queen is changed and queen cells are removed, the swarming impulse will probably subside
• Colony division or artificial swarm (see chapter 8.1)
• Super reversal in spring (see chapter 8.2)
• Apply the Demaree method (or checkerboard method). Its principal objective is to separate the open brood, including the eggs, from the queen (see chapter 8.3)
• Apply the Virdis method: transfer of capped brood into a 2nd super above the first (see chapter 8.4)
• Queen caging (method currently being tested by Serge Imboden and Claude Pfefferlé, Beekeeping Society of Sion: www.apision.ch): See chapter 8.5 and the article: ► Extinguishing the swarming impulse

 

8.1 Method 1: Artificial Swarm

(see article: ► Nucleus colony formation)

Workflow:

• capture the queen of the parent colony and place her in a queen cage
• place the cage with the queen of the parent colony or a newly reared breeder queen into a swarm box (or into a nucleus box 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 the artificial swarm a small amount of liquid feed
• place 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 nucleus apiary approximately 3 km away with frames of foundation and release the queen (if the artificial swarm is to be located at the same site as before, it must remain in the cellar for at least 4 nights and be fed)
• first inspection after 7 days (check whether the queen has been accepted; if not, introduce a new queen, check number of bees, food supply, etc.)
• treat the nucleus colony with oxalic acid (by spraying, trickling or vaporisation)
• inspect the donor colony (queen cells, presence of the queen, egg laying)

See also:

► Artificial swarm
► Artificial swarm with queen

 

8.2 Method 2: Super Reversal

(see also the article: ► Understanding swarming)

An easy method is super reversal in spring. It applies primarily to colonies that have overwintered on two supers, although it can also be applied, after the addition of a second brood super, to colonies that have overwintered on a single super, whether outside or in a cellar. The principle is as follows:

Bees in hives overwintered outside on two supers consume their syrup throughout winter by gradually moving up into the top super. Normally, at the end of winter, the bee cluster is located in the top super, with the bottom one empty. The queen therefore begins her egg laying in the top super. By reversing the supers at this point, the empty space is placed above the cluster and the brood, which is more natural for the colony. The queen can then move up to lay in this empty super. The supers can be reversed again a few weeks later, when the brood in the bottom super is in the process of emerging, so as to place this new free space at the top of the colony again. This ensures that the queen always has sufficient space for egg laying, and also maximises the number of foragers that will take to the field when the nectar flow arrives.

8.3 Method 3: The Demaree Method

An effective means of swarm prevention is the Demaree procedure. This procedure was devised by George Demaree and presented for the first time in the American Bee Journal in 1884. Its principal objective is to separate the open brood, including the eggs, from the queen. The brood is placed above a queen excluder while the queen is kept below. This procedure reduces overcrowding of the hive and its swarming impulse. It thus makes it possible to retain the entire bee population and maximise honey production.

This involves creating an artificial swarm without physically separating the colony. All the brood – except one good frame of larvae and capped cells – is transferred into a super that is placed on top of the honey supers (for Dadant hives: 2 stacked supers). In the bottom super, one food frame, the brood frame (with the queen), and 8 empty drawn frames are left. The queen excluder is then placed between the bottom super and the honey supers.

• The queen thus has 8 frames available for egg laying. The majority of bees remain above with the brood but will descend as it emerges. They will eventually fill the upper brood super with honey.
• Since the bees remaining with the upper brood no longer "smell" the queen below, they will believe themselves to be queenless and will attempt to raise a new queen from eggs present in the combs. It is therefore important to return and destroy ALL queen cells present on the combs of the upper super one week to ten days after the operation.
• This procedure leads the bees to "believe" that swarming has taken place; moreover, this sudden addition of egg-laying space for the queen will noticeably increase the colony's population in the following weeks.

This plan is initially designed to reduce or suppress swarming by separating the queen from virtually all of her brood, forcing the nurse bees to leave her to attend the nursery separated by an excluder and located at the top. The conditions for swarming are therefore no longer present at this point; it amounts to swarming within the hive. It is applied to a strong colony, but if the objective is to obtain queen cells, the operation can be performed on a colony of average strength. The advantage of this plan, which requires little time to implement, is that the always tedious search for the queen is avoided, that the bees retain the same odour, and that the honey harvest will be substantial if weather and forage conditions are favourable. There is no colony division and no picking.

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See also:

• Understanding swarming
• Queen cells
• Colony division
• Pheromones – semiochemical communication