The Choreography of a Swarm: A Deeper Dive into Honey Bee Machinations
By Maren Vickers, TTP Summer Technician
Honey bee swarms are a nuisance that every beekeeper is familiar with, as they are a natural part of the hive’s reproduction behaviour. While generally indicating a very strong colony, the consequences afterwards are unsavory: half your bees gone, a wild hive in an unknown location, a virgin queen that needs to be mated (slowing down colony production), and a biosecurity risk to evaluate. However, as inconvenient as swarms are, they are also a fascinating display of physical, visual, and hormonal communication between bees. Finding a new home is quite the event!
Swarming Criteria
Before the colony decides to swarm, there are three major criteria a colony must fulfill to signal its necessity (Figure 1). The first and most obvious is overcrowding: too many bees are in one colony, and there is simply not enough space to accommodate them all. With the queen continually laying, the population will continue to grow, further escalating the congestion. This point is typically reached when 90% of the comb is occupied by brood, honey, and pollen (Grozinger et al. 2013).
The second factor is a reduction in Queen Mandibular pheromone (QMP); usually QMP stops queen cell production within a hive even if it’s congested (Richards et al. 2015). However, a high volume of bees
Figure 1: The three criteria that signal a hive may swarm.
within the colony can dilute the QMP significantly enough to overcome its effect. A queen may also have lower levels of QMP due to old age. In either case, this hormonal reduction stimulates the bees to begin producing queen cells to replace the queen when she swarms.
The third factor is the ratio of bees to brood. Once there is a surplus of bees to care for the quantity of brood, the workforce has reached a point where the loss of bees to a swarm would not be harmful to the original colony. Considering swarms are a natural way to grow bee populations in an area, it would be counterproductive to swarm if it guaranteed the parent colony’s demise. Ensuring there is a sufficient workforce to upkeep the colony after swarming is critical.
These three colony-based criteria all interact and amplify each other to initiate the preparation of a swarm by the bees (Figure 1). However, the precise trigger for a swarm is still unknown (Grozinger et al. 2013). For example, a highly congested colony by itself does not guarantee a swarm will occur. Neither does the production of queen cells due to low QMP. Rather, the accumulation of factors summates to warrant a swarm. al environment of the colony and the bees themselves in the machinations of the swarm.
Swarming Preparation
In order to start the swarming process, bees must partake in certain preparations. These occur at the individual, colony, and caste level, with a host of stimuli directing movements (Table 1.1).
At the colony level, scout bees (older bees that assume guiding responsibilities) begin peremptory waggle dances, searching for a new nest location. Closer to bivouac formation, these scouts initiate several physical and auditory stimuli to increase the worker bees’ metabolic rates to the necessary flight temperature. Since bees require their thoracic flight muscles to reach a minimum of 33°C for rapid flight, a collective effort of piping, buzz running, and shaking signals allows assimilation to this state for effective take-off (Seeley et al. 2001) (Table 1.1). Remember, it is nearly 10,000 bees that must all be prepared at the same time.
Table 1. Description of each stage of swarming and its associated stimulus. There may be multiple actions per stimuli.
Piping is one of the earlier signals, beginning 6-10 days before bivouac formation, with increased intensity in the hour before swarm departure (Grozinger et al. 2013). This auditory stimulus is created when the queen or workers set their thorax on the ground and push their wings together while vibrating them for 0.2-2.0s at 100-250 Hz (Seeley & Tautz 2001). The subsequent high frequency sound signals for increased activity and is initiated by the nest-seeking scouts.
Buzz running is exactly as it is named: bees (activators) run through the hive in a zig-zag pattern while periodically buzzing, and in doing so, stimulating other bees (unactivated) into activity (activated). This phenomenon is displayed before bivouac formation, as well as in the bivouac before the swarming flight. As seen in Figure 2, contact between unactivated bees and buzz running individuals (activators) quickly transmits the signal to warm-up and get ready for flight. Generally, this stimulation begins shortly before departure.
Figure 2: The process of buzzing runs breaking up a clump of inactive bees to prepare for sustained flight.
Different from buzz running, but with the same outcome, is the shaking signal (or vibration signal) (Grozinger et al. 2013). Here, scout bees will contact another bee and “shake them” by grabbing and moving them dorso-. Shaking may be used at any time within a hive but is increasingly utilized before bivouac formation and before the swarming flight.
At the individual level, bees intending to swarm will engorge themselves on food in the days leading up to take-off to have enough sustenance to endure the swarming process. This is done by storing nectar in their crop to use throughout the journey. O It is imperative they conserve heat and energy as the swarm flight is energetically taxing, so leaving the bivouac would not be practical. Instead, the bees will lower their metabolic activity and use the food stored in their crop (Seeley et al. 2003). Foraging for resources will occur only after landing at their final destination. Additionally, as it takes about a month for the new hive to produce adult bees, the more fat reserves the swarming bees have, the higher their chances of survival. As such, mainly young individuals are selected to swarm to overcome this gap between resource foraging and the emergence of new bees.
Now metabolically and physically ready for flight, the swarming bees are finally ready for take-off, and the trigger can be set off to begin their journey to a new nest!
Bivouac Activities
Having finally taken-off from the hive, the bees form the bivouac. Should multiple clumps form in different areas, the landing place of the queen will attract the separated bees to form a single clump as the queen pheromone is released (Table 1.2). This bivouac stage can last anywhere from 1-4 days; that is, until the scout bees have located a new permanent nest site (Camazine et al. 1999). With a search radius of up to 150km2, there is a lot of ground to cover! There are many factors that scouts must consider for a new home, as discussed by Camazine (1999). A few of these include “volume, exposure, entrance size, and height from the ground” (Camazine et al. 1999). Once a scout has appraised a spot to meet these parameters, she will return to the bivouac and perform recruitment dances (alternative waggle dances) for the other scouts, to convince them this location is favorable. Some scouts will travel directly to the location to evaluate the nest site after receiving the message, but most scouts are swayed based on enthusiasm and dancing length. The more enthusiastic a bee is during recruitment dancing, paired with a longer sequence, the better the nest quality. The message is further amplified once a sufficient number of bees are convinced of the site’s caliber in accordance with their nature; that is, the phenomenon wherein individuals of a social group are influenced into collective activity by the actions of a few: similar to a large-scale and complex ‘follow the leader’ effect. As such, it enough scouts convinced by one bee, recruitment dances will cease, and the swarm will begin preparations for flight once more – the trigger likely initiated by the scouts.
Similar to ‘Swarming Stage 1’, piping, buzz running, and shaking signal activity begins to warm body temperatures up to flight-ready. During bivouac suspension, bees huddle together and decrease their body temperature to around 15°C to conserve heat and energy, maintaining higher temperatures only around the queen near the center (Seeley et al. 2003). Therefore, warming-up is necessary for successful rapid flying. From there, they form their swarm in unison, all abuzz.
Figure 3: The process of scout bees streaking through the swarm to influence the direction of movement. Bees will deviate their course in the direction the ‘streaker’ is travelling
The Swarming Flight
Many animals display herding, swarming, or migratory behavior, and to do so successfully, employ their own creative methods. Bees rely on a herding-like system to move. Similar to dogs herding sheep, there are a low number of scout bees that are in charge of guiding the rest of the uninformed colony. However, instead of moving around the other bees to incite change in direction, certain bees called ‘streakers’ zoom through the swarm (faster than the other bees) in the direction the swarm needs to go (Table 1.3). The action of streaking pulls the other bees along the line the streaker bee is moving, therefore slightly changing course. With consistent streaking behavior, the uninformed bees are kept on track during flight towards their destination, and even guided around physical barriers (Janson et al. 2005) (Fig. 3). This all happens while the swarm is moving at up to 7km/h (Beekman et al. 2006).
Approximately 80 m before the nest site is reached, scout bees will cease streaking (Janson et al. 2005). With no direction, uninformed bees will lose velocity until they are at a standstill around 10 m from the nesting cavity. It takes a long time for the swarm to slow down! During this time, scout bees will enter the new nest and release attraction signals from their gland (a gland in their abdomen that produces attraction pheromones) (Table 1.4). The chemical signal tells the swarm “this is our new home” and accelerates acceptance of the colony to the location (Janson et al. 2005).
With a new hive to build, the bees will be under significant pressure for the first month, after which stability and growth will recommence; comb will have been built, resources gathered, and new bees emerging to replace the old swarmed bees. A new beginning will be established by a variety of physical, auditory, visual, and chemical signals that developed a choreography of movement interlinking thousands of honey bees. This sophisticated communication continues to be a wonder of the animal kingdom, representing the intelligence of life in our everyday world.
References:
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