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.
 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."
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