"Each bee on her return is followed by three or four companions . . . how they do it has not yet been observed" Aristotle, Historia Animalium, IX
"In the summer of 1944 a few very simple experiments led to a result that was just as unexpected as it was thrilling" Karl von Frisch on the discovery of the dance language of bees
Soon after the end of World War II in war ravaged Germany, Frisch was observing the dance of bees and "reading" the language he himself had recently deciphered. In a way, he was feeling ecstatic: he could eavesdrop in the bee conversation and interpret their symbolic language. He understood the eight-shaped dance meant, for example, nectar 1.5 km away and at 30 degrees from the current position of the sun. On several occasions he had astonished neighbors by telling them that his bees were feeding from sources on their farms which he had not seen. The human and insect brain had never communicated in such a way before. But at the same time he was baffled.
How could the bee know the position of the sun? At that time he was studying the bee dance on a comb placed horizontally. Previous experiments had proven conclusively that bees used the sun as a compass. He could even rotate at will the dance by replacing the sun with a lamp. If the horizontal comb was covered and illuminated by diffuse light, the dances were disoriented. But somehow they became oriented again if the bee could see a small patch of blue sky. As hard as it was to believe at the time, Frisch concluded that the bee could see the polarization pattern of the sky! Later, other researchers discovered many other animals sensitive to polarized light (eyes), some of which could use it for navigation, as the bee does. But this capacity was discovered in honeybees first because they gave away their secret through their dance language.
The Dance Floor
Bees returning to the beehive after finding a good supply of food will communicate to other bees by dancing at a particular region in the comb: the dance floor. The dance floor is generally close to the entrance but sometimes moves, e.g. goes further inside when it is cold or closer to the entrance when there is lots of activity. In Nature honey combs are vertical, so the dance is generally performed on a vertical plane. This is of great significance for the bee dance as the language must provide information of horizontal directions on a vertical plane. However, when the weather is very warm the dance floor may move outside the entrance to a horizontal flight board. It is also horizontal in some primitive bee species and can always be made horizontal by the human experimenter. Dances on oblique dancing floors can also happen, mainly on the obliquely rounded lower edge of a free-hanging comb or on the rounded swarm cluster bees form when looking for a new nesting place. Notice that in nature the vertical dancing floor is inside the hive and thus quite dark while the horizontal one is generally under the open sky.
The Bee Dancing Repertoire
Round Dance
When a foraging bee finds food close to the beehive, it performs its simplest dance, the Round Dance. This dance doesn't provide much information, it is more of an arousal signal. The forager bee runs in a small circle, leaving a single cell inside it. Every one or two circles it suddenly reverses orientation and this goes on from seconds to minutes. The bees recruited follow the dancer on the floor and then fly off by themselves looking for the food. If these bees haven't been feeding at a particular place before, they will look for food in every direction in the proximity of the beehive. However, the dancing bee also gives away odors that can be recognized by bees frequenting the same flowers, who will fly directly to them.
Tail-Wagging Dance
When the goal is further away, the bees need more sophisticated means of communication. If food is scarce, bees have been known to feed up to about 15 km (~10 miles) from the beehive. In relation to the small size of this animal these distances are outstanding. Although a bee flying to a known source of food uses as references conspicuous landmarks in addition to the sun compass, it can only communicate information about the latter to fellow bees. The Tail-Wagging dance tells the other bees very accurately at what distance and in which direction the food is, so they can look for it by themselves. Some European honeybees start to perform it when the source of food is more than 100 meters away. Other bee species will do them for closer sources, up to just a few meters away in the case of some Indian bees. For intermediate distances there is a gradual transition between the round dance and the tail-wagging dance.
In a typical tail-wagging dance the honeybee (Apis Melliphera) runs straight ahead for a short distance, returns in a semicircle to the starting point, again runs through the straight stretch, describes a semicircle in the opposite direction and so on in regular alternation. The straight part of the run is given particular emphasis by a vigorous wagging of the body (rapid rhythmic sidewise deflections). In addition, during the tail-wagging portion of the dance it emits a buzzing sound. Interestingly, the dance followers can make the dancer pause and give them a taste of the nectar by using a squeaking sound.
Distance Information
With increasing distance the number of circuits (8's) per unit time decreases and the length and duration of the individual circuits increases. For example, for a goal at 100 meters it makes 10 short circuits in 15 seconds but at 3 km only 3 long circuits in the same time. The duration of the wagging part has the best correlation with distance. The distance is calculated based on the expenditure of energy on the flight towards the source (a head-wind increases it). Each recruited bee averages many dance circuits or even several dances from different bees to calculate the distance. For each bee species a distance-frequency curve can be plotted. It is remarkably precise, especially if the distance is not close to their foraging range limit.
Compass Information
If the dance floor is horizontal (the least common case in Nature), the indication of direction is straight-forward: the wagging (straight) portion of the eight-figure dance points towards the food source (and in the same direction as the bee runs through it). But, what does the dancing bee use as compass to accurately point in the right direction? The bee reference is the direction of the sun. This can be demonstrated easily by covering the sky and using a lamp as an artificial sun: the direction of dancing will rotate, always maintaining the same angle with the lamp as the angle with the sun during direct flight towards the food.
If the dance floor is vertical the indication of direction requires a higher-level language that can communicate horizontal directions with an indirect, symbolic, representation. In a vertical plane the natural reference is gravity, so the dancer replaces the real reference, the sun, by the "UP" direction. For example, if the bee maintained the sun 70 degrees to her left when flying towards the nectar, the wagging portion of her dance will point 70 degrees in the clockwise direction from the upwards vertical direction. The bee transposes the solar angle into a gravitational angle! On an oblique comb the gravitational transposition works well up to an angle of about 10 degrees to the horizontal.
Steering by Polarized Light
The light from the blue sky is polarized and the direction of polarization at each point depends on the position of the sun, as described elsewhere in this site (Polarization.com has developed an educational Skylight Compass Card.). When the bee cannot directly see the sun, it will infer its position from the polarization pattern of the blue sky. Bees can use this "sense" when flying to a goal or when communicating directions to other bees. For example, they can maintain course under the shadow of a mountain, at twilight, or when only small patches of sky are not clouded. But, attention, their ultraviolet vision can often see the sun through clouds: remember what your mother told you about sun burns on cloudy "cool" days.
On a horizontal dance floor a patch of blue sky is enough for directing the dance towards the food. On a vertical dance floor the bee usually doesn't see the sky and the dance is steered by gravity. But if the bee can see a piece of sky then she will point towards the bisector of the angles determined from the gravity representation of the sun and the polarization-inferred position of the real sun.
Bees orient just as well relative to the polarized light of the blue sky as to the sun itself (only the azimuth of the sun matters, not its elevation above the horizon). However, if the bee can only see a small portion of the sky the polarization pattern may be ambiguous in determining the direction: the bee may point and fly in the correct direction or just in the exact opposite. If neither the sun or the sky are visible in a horizontal dance floor, then the dance becomes completely disoriented. A patch of sky near the sun is not useful as it is not polarized.
The marvelous experiment of rotating the direction of the dance by moving an artificial sun has a counterpart with polarized light. Rotating a polarizing filter in front of the blue sky (with the sun blocked) rotates the dance in sync! I can image such an experiment: it's eerie.
Honeybees can detect polarization in the blue and ultraviolet, but not in the green and yellow. Bees are very sensitive to polarization: they only need between 7 and 10% degree of polarization to orient themselves. Elsewhere in this site we discuss the biological basis of the sensitivity to polarized light of insects and other animals.
Bees need to learn from experience the polarization pattern of the sky, the same way they learn the local trajectory of the sun. However, some spontaneous orientation in preferred directions with respect to the plane of linearly polarized light (0°, 45°, 90°) has also been reported.
Democracy among the bees: dancing and voting
When it comes to choosing a new house to move, the queen has no vote. Swarming is one of the most interesting events in the life of bees. This is how new colonies of bees are created in Nature. In spring, when food is plentiful, about half of the colony leaves the hive, following the mother queen (young queen candidates have been raised in advance to the take over the old house). The moving bees first settle nearby, where they form a swarm structure with their own interlocked bodies hanging, for example, from a branch (true swarming is not seen in the apiary as the beekeeper will immediately surround the swarm with a box). The hanging swarm is well structured: its interior consists of loosely branching chains of bees that leave between them enough space for other bees to pass; its exterior is formed by about three layers of living bees, with just one entrance to the interior.
In 1955 Lindauer was the first one to describe the natural swarming behavior and the dance role in finding the new nesting site. Scout bees leave the swarm to explore for an adequate home and after finding one return to the swarm where they perform wagging dances to "vote" for the location. Other bees then take a look at that location and a voting process that may take from hours to several days goes on. In an exemplary display of democracy ("mother queen" is an spectator), the bees slowly converge to an agreement and most of the dances finally point to the same location. Of course, the most vehement dancers tend to win over the rest. After agreement the swarm dissolves and all the bees fly to their new homestead. Lindauer described how he could often beat the swarm to the new nesting place by "reading" their dance language. He also described a few instances when the voting remained divided, which can be catastrophic as, unfortunately, the queen cannot be cut into two (Vive la Republic!)
Taking a nap, hauling water, and pointing through walls
Brick laying. The same dance language that foragers use to indicate a source of nectar or pollen is also used to indicate the location of a source of resin. Resin for cementing (propolis) is gathered mainly from buds on trees. It is brought in like pollen in the baskets on the legs and is used for sealing cracks in the hive.
Hauling water. The wagging dance is also used to indicate water sources. Water is required by the young bees that take care of the brood and for regulation of the hive temperature. Although bees are poikilothermic individually, they maintain a constant temperature in the brood nest between 34.5 and 35.5 degrees C. The bees can generate warm by clustering together and vibrating their muscles. They cool the beehive by first fanning and if this is not enough by depositing water in the cells so they are cooled by evaporation. For example, Lindauer placed a beehive on a lava field in Salerno, Italy, under full sun, which raised the exterior temperature to more than 70C (158F): the bees were still able to maintain the internal hive temperature as long as they could collect water nearby.
Tropical siesta. Working bees? When the sun is less than 3 degrees from the zenith, tropical bees don't go out to forage. This is because they are unable to use the sun as compass when it is so high.
Say Up, say Down. The language of the bee has no expressions for the directions upward and downward (mischievous researchers have placed beehives on towers and bridges).
Pointing through buildings and mountains. Bees indicate the direction of the air line towards the food source, even if they take a detour to get there. Thus, they somehow "integrate" the flight path (as long as no portion of the path is darkened). For example, if a bee goes around a building to collect nectar, it will still indicate the direction of the source "through" the building. Thus, recruited bees will try to fly over the building. This ability is useful for scout bees, which may have discovered the food source by many detours. However, the distance indication corresponds to their true flight.
Another dance. With nearby sources of food, tail-wagging dances with two diverging straight segments are often seen: the bisector points in the direction of the goal.
No Windsock. Even if the bee flies with crosswind and has to rotate the flight direction with respect to the sun to compensate for it, the dance will point straight to the food source.
Confused but not Misguided. Under some conditions the solar angle indicated in the dance may deviate appreciably from the true solar angle. This happens on the vertical dance when the bee can perceive the sun (or a piece of blue sky). Then the dance points towards the bisector of the directions that would occur for a purely gravitational reference and a light reference. There is also a residual gravity error in the angles: the direction tends to shift towards the vertical or towards the horizontal, whichever is closer. But in neither case it results in a misdirection: the dance followers are subjected to the same influences as the dance leader and understand the language correctly.
Party Animals! The bees compensate for the diurnal movement of the sun in the sky and rotate their dance and flight direction in accordance. In fact, a few overzealous bees that continue dancing for hours can (under diffuse lighting) dance the night away, following the sun in its travel below the horizon! However, they have to learn at some time in their life the rate of movement of the sun in the sky at that location, as it is not innate (but they can extrapolate the whole thing from just a few hours of the day).
Truly Amazing Bees
Few animals are more amazing than honeybees. They live in an intricate society, with queens, guards, builders, cleaners, nurses, heating and cooling technicians, scouts, honey makers, pollen stampers, and collectors of nectar, pollen, water, and resin (each worker bee goes through many different "jobs" during her lifetime). They build complex hives with beautiful honeycombs of perfect hexagons. They make flowering plants and honey-lovers thrive. They accomplish great feats of navigation. They see more colors and smell more scents than we do. They see the polarization pattern in the sky. And they communicate information in a symbolic language without match in the animal kingdom: the bee dance.
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[1] Karl von Frisch, The Dance Language and Orientation of Bees, Harvard University Press, 1967.
Karl von Frisch (1886-1982) shared the 1973 Nobel Prize in Physiology and Medicine with Konrad Lorenz and Nikolaas Tinbergen. Tinbergen recalled from a pre-war visit to Frisch's laboratory in Munich: "My recollection of that visit is a mixture of delight with the man Von Frisch, and an anxiety on his behalf when I saw that he refused to reply to a student's aggressive Heil Hitler by anything but a quiet Grüss Gott."
