By Sandra Tuszynska
Bees have different roles in the hive and one of those roles is that of a scout. Scouts search for new sources of food. Once a scout bee locates a source of food that is economically and nutritionally suitable to her colony’s requirements, she comes back to the hive with the good news. She must now let her sisters know that she has found the best food source that there is on offer. However, how does the scout bee inform her sisters of the exact location of this newly found food source and convince them that they should go and check it out?
Bees have an ingenuous communication system which is expressed through an intricately choreographed dance routine. In 1973 Karl von Frisch, received the Nobel Prize for interpreting this highly sophisticated, navigational dance-language of bees. The “waggle dance” otherwise known as the recruitment dance, is an immaculately precise communication system involving movement, geometry, sound and smell. The dancer is nothing less than a mathematical genius that can portray the distance, direction and other essential information about the food source, through her superb choreography.
THE GEOMETRY OF THE WAGGLE DANCE
There are in fact at least three types of dances that bees engage depending on the distance of the food source from the hive. If the location is within 50 metres, the domestic honeybee, Apis mellifera, performs “the round” dance (Tarpy, NCSU). The round dance explains the distance but it is still unclear whether it explains the direction of the food source Dyer, 2002). If the food source is within 50-150 metres, the bee dances the sickle dance, which is a transitional dance between the round and the waggle dances (Tarpy, NCSU). However, if the food source is further than 150 metres from the hive, the bee performs the “waggle dance” (ApisUK, 1014). There are other types of dances used for communication of information not related to sourcing food, but activities such as migration and swarming.
The waggle or recruitment dance is a form of communication system that requires highly sophisticated spacial-information processing. The scout bee must first measure the distance from the hive to the food source and its direction in relation to the sun (Dyer, 2002). If the sun and the food source are in the same direction, the bee dances directly upwards on the honey comb dance floor of its hive, in a vertical straight line called the “waggle run”. If the food source is at a particular angle away from the sun, the bee will dance at that particular angle from the vertical line to demonstrate the angle of the food source in relation to the sun (ApisUK, 2014).
Bees use the solar compass or gravity for spacial orientation. If the sun happens to be behind a cloud, bees use a patch of a blue sky and the polarised light that it reflects as a directional cue. But what happens on a cloudy day? It turns out that bees recognise land marks and can create a path to food by reference to land marks, and even learn and memorise the position of the sun relative to land marks (Dyer, 2002). Bees can work out the sun’s position from the direction of a land mark based on their circadian rhythm, in order to get to a food source on a cloudy day.
Bees actually learn the pattern of solar movement relative to the season and latitude at which they live, within a few days of becoming foragers (Dyer, 2002). Even though young bees have not been able to observe a full day’s sun movement, these incredible creatures possess an inbuilt template of the general patterns in which the sun moves (Dyer, 2002). All bees are born knowing the directions of the sun rise, sun set and how it crosses over during midday. This template is continually updated as they learn more about sun movements, while on the job.
The bee waggles from side to side, while her wings produce a buzzing sound as she performs the waggle run. At the end of the waggle run, the dancer will either turn left or right circling back to the beginning of the run. She will repeat the waggle run and then return in the opposite direction. When the dance is mapped out, it is in the shape of a coffee bean or a squashed figure eight. The geometric shape of the dance changes with changes in the distance to the food source (Frank, 1997). The shorter the distance of the food source to the hive, the shorter the waggle line. At a certain distance the two round shapes split off from one another becoming two separate or divergent waggle runs. When the food source is closer than 50 metres from the hive, the dance becomes a “round dance” taking on a completely different geometric shape (Frank, 1997).
TRANSLATING THE DANCE
The duration of the dance, divulges the distance a bee needs to travel to the food source, the longer the dance the longer the distance. This relationship is almost linear, for example if the waggle run lasts 2.5 seconds, the food source is located about 2 625 meters away (Tarpy, NCSU). But how can a bee measure the distance without a speedometer? Their compound (multifaceted) eyes possess motion capture mechanism; providing a conglomeration of images of their world. To measure distance bees use “optic flow” – the movement-induced streaming of visual texture across a visual field (Dyer, 2002).
In other words, their compound eyes are sensitive to the “flickering effect” of complex moving objects and the richer the imagery, the greater the distance they perceive (ApisUK, 2014). This means that a bee will perceive a shorter distance if it flies over a calm lake, which provides a weak optic flow, compared to flying over the same lake while roughened up by the wind, providing a stronger optic flow (Dyer, 2002). Bees therefore translate optic flow information, through the duration of their dance into flight distance to the food source.
The waggle dance has a set of specific parameters that the bee uses to communicate the distance related information needed by her mates. The tempo of the dance is fast if the food is near and decreases with flight distance (Dyer, 2002). The tempo is the time it takes a dancer to complete a particular number of dance circuits. A circuit includes the waggling run and the return run before the next circuit begins. While the dance gets slower, the duration of the the dance circuit increases with distance.
The number of waggling runs a scout bee performs indicates the overall value of the resource, including its profitability and how it meets specific colony requirements. Another way to communicate the value of the food source seems to be reflected by the overall excitement of the dancer, the more vigorous the dance, the greater the value of the food resource (Dyer, 2002).
Other parameters also increase with flight distance, including run duration, number of waggles from side to side and the duration of the sound bursts the bee produces while dancing (Dyer, 2002). The buzzing sound bursts are of low audio frequency of 250 to 300 hertz or cycles per second, and are delivered at a rate of about 30 sound bursts per second, lasting around 20 milliseconds each (Tarpy, NCSU). The duration of sound bursts is correlated with distance of the flight. Sound seems to only play an important role in communicating distance while in the dark confines of the hive. However in open-nesting bee species, visual cues such as posture and movement play a key role, while the dancers are silent (Dyer, 2002).
It is important to remember that the dance occurs in complete darkness of the hive in many bee species. So how do the spectator bees pick up all this information from the performing scout? Bees recognise the cues of the dancer through the sound waves produced by her wings, which the spectating bees detect through their antennae (Dyer, 2002). The vibration of the honey comb is also detected by sensory receptor cells, along with tactile cues through physical contact between the dancer and the spectators (Dyer, 2002) .
Bees are excellent mathematicians as they can compensate for taking different routes to a particular food site using a process called path integration to derive parameters for the most direct flight (Dyer, 2002). The dancing bee must incorporate the path integration information into her dance. On the receiving end, recruited bees will need to translate the the information received through the dance into the actual flight and the sensory information provided by the environment outside the nest (Dyer, 2002). They must take into account that the sun has changed its position since the scout has left in search for the food source, as well as environmental factors such as the wind and topography, which result in variation in perceived flight distance (Dyer, 2002).
Scent and smell
The scout bee also picks up molecules from the environment such as the scent of the flowers that she has visited, which her forager mates recognise and use as a source of information in finding the correct food source (Dyer, 2002). Odour cues work best if the food source is relatively close to home. Bees also release pheromones, chemical messengers similar to hormones, which are used to communicate with one another (Dyer, 2002). Each pheromone or scent that the bee produces communicates a different message. Perhaps the chemical signal could be translated into something like this – “Do you remember, those great mango flowers down by the river, 3km from home? Thy are in flower again!” These chemical signals are released during the recruit dance, greatly contributing to the reliability of the information.
Even though we have seemingly come a long way since Von Frisch first began to investigate the dance language of bees in the 1960s, all that we know so far is still not sufficient to explain how a tiny bee can do what it does. Karl von Frisch himself described the honey bees and their dance language as a “magic well” of information and said that “the more you draw from it the more there is to draw” (Dyer, 2002). We simply do not understand the depths of intelligence encoded in these magnificent creatures as they continue to baffle scientists. What else is there to discover about the bees, one of the most studies and yet most secretive species?
ApisUK Beekeeping Science and news (2014). Honeybee Communication. Retrieved from http://apisuk.com/Bees/2013/09/research-%E2%80%93-mysterious-%E2%80%9Cquantum%E2%80%9D-dance-of-the-bees/
Dyer F.D. (2002). The Biology of the Dance Language. Annu. Rev. Entomol. 47:917–49
Frank A., 1997 (November). Quantum Honeybees. How could bees of little brain come up with anything as complex as a dance language? Discover – Science for the Curious. Retrieved from http://discovermagazine.com/1997/nov/quantumhoneybees1263
Tarpy D. R., (n.d.) The Honey Bee Dance Language. New Carolina State University. North Carolina Cooperative Extension Service.