Bees do not just reproduce through rearing new bees in the colony, sometimes they decide to split the entire colony and create a new colony elsewhere. Beekeepers are rarely happy when such a swarm takes off, especially as this often leads to losses in honey production. Nevertheless, swarming is the nature of bees.

The swarming vibe, are we going yet?

Time to swarm

In spring bees are able to bring in lots of food and colonies can grow rapidly with up to 1000 bees per day. If the hive gets too crowded, the «queen’s substance» is no longer distributed sufficiently in the hive. Workers that cannot sense the queen substance will believe there is no queen present and start rearing new queen by building swarm cells[1]. Up to 25 queen larvae are fed with royal jelly until their cells are capped. Royal jelly is formed in the so-called hypopharyngeal glands, which are located in the head of the worker bees. Royal jelly is rich in vitamins, proteins, fats and minerals [2]. It is only this special diet that makes a larva develop into a queen. In contrast to the queen, the worker brood receives pollen and honey from the third day of its development.

Battle for the throne

Only one of the newly reared queens can ascend to the throne. The first-born queen therefore locates the unhatched queen cells and stabs her competitors through the cell wall. Here communication plays an important role. After hatching, the young queen will begin tooting, while queens that have not yet hatched respond to this with quacks. Because bee colonies usually construct a large number of swarm cells, each toot is answered by numerous quacks. It could be shown that the tooting suppresses the hatching of other queens. Also, the quacking noises probably enables the hatched queen to find the unhatched queens [3].

If two queens hatch at the same time, a fight to the death begins. Here the workers also influence the choice of the new queen. In case of several hatched young queens, the workers cheer on their favorite with vibration signals. Queens who receive the signal more often eliminate more rivals and are more likely to climb the throne [4].

Time to go

About a week before the new queens begin to hatch, the old queen leaves the hive together with about half of the colony. The swarm includes workers of all ages as well as some drones. Before the bees leave the hive, they refuel themselves with honey, since they must do without food reserves the coming days [2].

The bees use two signals to indicate when they are leaving the hive: they beep and perform the whir dance. The beeping begins more than an hour before take-off and causes the bees to warm up their wing muscles. The whir dance begins immediately before leaving the hive and is the signal of departure. Here, the bees run zigzag and flap their wings [5].

The Swarm

Finding a new home

Once the swarm has left the old nest, it gathers in the surrounding area and forms a cluster around the old queen. The workers recognize the queen by the queen’s substance and lure further workers to her by fanning the Nasanov pheromone. Now it is time to find a new nest. Scouts fly out and start searching the area within a radius of several kilometers. If a scout finds a possibly suitable location, she inspects it carefully for about half an hour. The volume of the nest is estimated by walking through the cavity. Cavities of 30-40 liters with small entrances are rated as particularly good. Further, bees prefer nests that are located off the ground and are not surrounded by dense vegetation [6].

Nesting

If the quality of the nest is satisfactory, the scout flies back to the swarm cluster and performs the waggle dance to show the other workers the location of the discovered nest. The quality of the nest is indicated by the number of rounds danced. The better the nest is judged by the dancing scout, the more scouts fly out to check it out too. If one nest is clearly superior, an unanimous decision on where to go is quickly reached. However, if there are several similarly good nests in the area, the decision process can take a long time. Nevertheless, the bees usually come to an agreement at some point. Scouts will stop dancers who advertise nests if they believe there is a better option. They will knock their head against the dancer with a 350 Hz (vibration signal). In this way a selection is made and even a absolute majority can be reached. This mechanism of positive and negative feedback actually works very similar to the neuronal networks of the brain, which is why we can speak of “swarm intelligence” [7-9].

Flight into the new nest

The scouts communicate impending departure by beeping (produced by vibration of the flight muscles), whereupon the bees of the swarm warm up their flight muscles. Similar to when leaving the hive, the final take-off is coordinated by the whir dance [10]. The swarm is now led by the scouts to the chosen nest. To navigate the thousands of bees, scouts fly repeatedly in the appropriate direction through the flying swarm [6].

Colony of the new queen

The wedding flight

When the new queen is around one week old, she will depart on her wedding flight. She is accompanied by some workers who protect the queen from possible dangers and will distract predators like wasps and birds. This squad goes to a drone congregation area, where up to 20,000 drones are waiting for virgin queens [2].

Drones are lured by the queen’s sexual pheromone. Which is produced by the mandible gland and consists of three substances ((2E)-9-oxo-2-decenoic acid (9-ODS), (2E)-10-hydroxydecebic acid (9-HDS) and 2E-10-hydroxydecenoic acid (10-HDS)). One substance attracts drones over long distances to the congregation area point (9-ODS), whereas the other two serve to recognize the queen in the crowd (9-HDA and 10-HDA) [11].

The queen mates in mid-air with up to 20 drones, the pairing itself takes only a few seconds [12]. During the mating the drones are torn from their genitals, which is why they die during mating. The queen, on the other hand, returns to the hive with enough sperm in her spermatheca to lay fertilized eggs for the next few years.

The subfamilies of the colony

The new bee colony consists of the descendants of the queen. If she has paired with several drones, the colony is formed from so-called subfamilies. The workers of a subfamily are full siblings of each other and the descendants of the same father, while they have only their mother in common with the other subfamilies (half siblings). It could be shown that this genetic diversity has a positive influence. Colonies with many subfamilies develop much better and are more productive than those with little genetic diversity (Figure 2) [13]. This is probably because many behaviors are also determined by genes. For example, the tendency of a bee to become a guardian is congenital. In a diverse colony, bees can thus complement each other better.