1. Introduction

Bees of the genus Apis display a highly social behaviour characterised by three criteria:

1.  Division of labour (polyethism), with the presence of a limited number of reproductive individuals (sometimes only one);
2.  Cooperation among individuals in rearing the offspring;
3.  Overlap of several generations within the group.

In addition, most social insects are distinguished by their ability to construct nests that sometimes exhibit elaborate architectures.

The advantages of group living include:

• Protection against predators
• Provisioning and communication of food sources
• Task sharing
• Functional rules with intergenerational cohesion

Group living also entails disadvantages:

Close contact, crowding, and an increased risk of disease and parasite transmission.

The influence of humans, through beekeeping practices and techniques, has remained largely without effect on the morphology, physiology, and behaviour of the honey bee.

The honey bee has never lost its ambiguous status: as a feral organism (swarm), it has been “domesticated” and hived by beekeepers. Nevertheless, it can regain its independence and swarm—sometimes repeatedly—and, in practice, follow its own biological imperatives.

2. Swarming: A Process, Not an Event

Unlike a simple division, swarming is a complex, finely orchestrated process. It unfolds over several weeks and involves the entire colony. From the earliest stages, careful preparation is initiated. Worker bees (or more accurately, the insect society), under the influence of multiple internal and external factors, begin structural and behavioural changes aimed at dividing the colony into two distinct groups: the bees that will depart with the old queen and those that will remain in the hive to receive a new queen.

This natural swarming cycle presents clear sanitary advantages:

It results in the construction of a new nest with new combs, leading to a reduction in parasite pressure (disruption of Varroa mite population dynamics) and other infectious pathologies.

The frequency of swarming follows a bimodal distribution, with a major peak in mid-May and a smaller peak in mid-August.

The duration of this process reflects the complexity of social interactions within the colony. Approximately fifteen days before departure, workers construct around a dozen queen cells in peripheral areas of the combs, signalling the imminent division. At the same time, the queen is placed on a restricted diet to reduce her body mass and prepare for flight. In parallel, specific acoustic signals begin to emerge within the colony, increasing in frequency as departure approaches.

Approximately ten days before swarming, the involved workers gorge themselves with honey, storing up to 35 milligrams per individual as an energy reserve for the journey. These bees, which form the future swarm, exhibit increasingly frenzied behaviour in response to acoustic signals emitted by their nestmates. In the final hours before departure, so-called “buzzing runs” occur, during which the bees vibrate and become highly active, thereby preparing the entire group for separation.

 

3. Biological and Environmental Triggers

Swarming is not a spontaneous reaction but the outcome of a combination of triggers. Internal factors include population growth, congestion of brood combs, and an increase in the number of young bees. These immature individuals contribute to the dilution of queen pheromones. Pheromones—volatile molecules produced by the queen—are essential for inhibiting the rearing of new queens and maintaining colony cohesion. When their concentration decreases, workers interpret this as a signal to initiate swarm preparation.

External conditions also play a crucial role. Seasonality, resource availability, and weather directly influence the likelihood of swarming. This behaviour is particularly frequent in spring, when floral resources are abundant and temperatures are favourable for flight.

4. The Departure: A Collective Choreography

When all conditions are met, the colony enters a spectacular transitional phase. The old queen, accompanied by 40 to 70% of the workers, leaves the hive in a swirling mass of bees. Despite its mobility, the swarm remains tightly coordinated thanks to the queen pheromone, which maintains group cohesion during flight.

The swarm travels only a short distance before temporarily settling on a nearby structure, such as a branch or a pole. This transient halt, often visible to observers, allows scout bees to explore the surroundings in search of a new nesting site. These experienced bees survey areas several kilometres away, seeking a protected cavity that offers sufficient volume, good thermal insulation, and easy access to resources.

 

5. Collective Decision-Making: The Art of the Scouts

Scout bees (representing only about 5% of the swarm’s individuals) play a central role in swarm migration. When they locate a potential site, they return to the swarm and perform a specific dance on the surface of the cluster. This dance conveys precise information regarding the direction, distance, and quality of the site. Other scouts, stimulated by this signal, then visit the site to assess its suitability.

This decision-making process is based on a quorum or a form of representative decision-making rather than full consensus. Once a sufficient number of scouts agree on the same site, they emit acoustic and vibratory signals to mobilise the entire swarm. Migration to the new site is then initiated and guided by “directive guidance”, in which hundreds of scouts rapidly cross and more slowly circle the swarm to steer the group.

 

6. The Parent Hive: A Necessary Reorganisation

In the parent hive, the departure of the swarm creates a complex transitional situation. Several virgin queens emerge, but only one can ultimately rule. The restoration of monogyny occurs through duels between queens, each attempting to eliminate her rivals. These often violent confrontations are punctuated by vibro-acoustic signals—the well-known “tooting” and “quacking”—which structure this competition.

Although worker bees are not directly involved in the fights, they play a regulatory role by sealing still-closed queen cells or favouring the emergence of a particular queen. These behaviours ensure the future stability of the colony.

7. Beekeeping Management: Anticipation and Prevention

For beekeepers, swarming can be a source of frustration but also an opportunity. Proactive management is essential to limit unwanted swarming. This includes regular replacement of ageing queens, ensuring sufficient brood space, and redistributing frames to prevent congestion. The creation of artificial swarms is a commonly used method to control this natural process while meeting the biological needs of the bees.

Technological advances, such as thermal and acoustic sensors, now make it possible to detect early warning signs of swarming. These tools offer beekeepers the opportunity to intervene rapidly and effectively, thereby reducing potential losses.

Reminder:

8. An Inspiring Natural Phenomenon

Swarming is far more than a beekeeping challenge: it is a compelling demonstration of collective intelligence in bees. Understanding its mechanisms and implications not only improves hive management but also deepens our appreciation of the complexity and resilience of bee colonies. Thanks to the research of Professor Hemmerlé and the accumulated experience of beekeepers, we now possess valuable knowledge to accompany bees through this ancestral process.

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See also:

• Pheromones: A True Semiochemical Communication
• Preventing Swarming
• The Waggle Dance of Bees
• Behaviour and Cognition: What a Mini Brain Can Teach Us