Karl von Frisch (1886–1982) was a professor of zoology at the University of Munich, and his favorite subject of study was bees. As a sensory physiologist and neuroethologist, he highlighted two key behaviours in bees that advanced scientific understanding: their spatial orientation and the secrets of their communication. For this work, he was awarded the Nobel Prize in Physiology or Medicine in 1973, along with Konrad Lorenz and Nikolaas Tinbergen.
Regarding the first point, it has long been known that desert ants can use the sun as a reference for orientation; this was discovered in 1911 by F. Santschi, a Swiss doctor working in Africa. Von Frisch went further, becoming the first to demonstrate that bees use the sun as a compass, helping them choose and maintain a specific spatial direction. This was in 1950, predating L. Pardi & F. Papi and G. Kramer, who independently demonstrated the phenomenon in 1952 for a small marine crustacean and for birds, respectively.
Having a solar compass means being able to compensate for its apparent hourly motion, maintaining a constant spatial direction throughout the day. The bee is thus able to return to the hive after an exploration, not only by recognizing memorized landscape details but also by using a fully developed cognitive map. We will see later that possessing a solar compass is a fundamental element of their communication.
A Little Bit of Bee Biology
Bees are social insects in the order Hymenoptera that have been associated with humans since the Neolithic era and have been effectively domesticated. For them, humans build hives containing vertical supports to hold the wax cells, called combs, where the queen lays her eggs, and the larvae are raised. The hive houses a fertile, reproductive queen and a large number of her sterile daughters, called workers. (Image 1) The workers live an average of about thirty days. During this short period, their tasks change with age (Image 2): initially, they are responsible for cleaning, then caring for the larvae, followed by building the wax cells, guarding and defending the hive, and finally, they become “foragers” who fly outside to collect pollen and flower nectar, the basis of their food and all the products we know so well, starting with honey.
Collecting pollen and nectar can be easy for a forager if the hive is located in the middle of a flowery meadow: just go out and refill the bees’ pollen sacs, then bring them back. But it’s rarely that simple. The forager must do considerable scouting of the surrounding area, sometimes traveling several hundred meters or more. If it finds good places to forage, it faces the challenge of calling its companions, “spreading the news,” and communicating precisely where to gather to ensure success and speed.
Dances as Language
Von Frisch spent a lifetime observing the behaviour of foragers, writing one of the most significant chapters in animal communication. He realized that a forager bee returning to the hive with good news would attract the attention of other foragers by performing a dance in a designated area of the honeycomb. This dance could take two forms: a circular pattern or a figure-eight pattern (Images 3 a and b). In the first case, the information transmitted is very simple: essentially an invitation to leave in search of a nearby food source, clearly visible and detectable even by smell due to the scent of the other bee. It is a form of social activation of food-seeking behaviour.
With the figure-eight or tail-wagging dance, the forager indicates a distant food source, conveying both its distance and direction. As shown in Image 3b, the bee traces a circuit on the vertical surface of the honeycomb, consisting of a central straight section and two elliptical wings, traversed alternately clockwise and counterclockwise. The distance to the food source is indicated by both the frequency with which the bee completes its circuit (the slower it completes the circuit, the farther away the destination is, as shown in Image 4) and the speed at which it travels the central straight section, moving its abdomen (wagging its tail) and emitting a rhythmic buzzing sound. In this case, the faster it moves, the farther away the food source.
The direction to fly is indicated by the angle that the central straight line forms with the vertical (the gravity vector). This angle is what a forager must maintain relative to the sun to head toward food (Image 5), highlighting the importance of using a solar compass in this case. As time passes and the apparent motion of the sun progresses, a bee aiming to continue toward the same point must adjust the angle it maintains with the sun, whose azimuthal displacement (the projection of its position on the horizon) is approximately 15° per hour.
The central part can be travelled from bottom to top or vice versa, indicating whether to fly toward the sun or away from it (Image 6). The figure-eight dance in Image 2b, for example, indicates that the bee must fly directly toward the sun, since the wagging part moves upward and vertically, that is, at a 0° angle relative to gravity. But what if the sun is not directly visible? In this case, bees can detect their position based on the plane of polarisation of light, to which they are highly sensitive.
But how reliable and, above all, comprehensible is this type of information given by a forager bee to her fellow bees? The experiments shown in Images 7 and 8 provide a clear idea. In the test shown in Image 7, von Frisch trained a forager bee to visit a saucer filled with a saturated sugar solution, placed at a specific distance. As the bee returned to the hive to alert its fellow bees, it placed other identical saucers before and after the original one, which it then removed. The alerted bees mostly headed for the two saucers closest to the original location. He used the same method in the experiment shown in Image 8, arranging the saucers in a fan shape at different angles, and again, the bees were unaffected by the angle the forager bee indicated.
Un fatto interessante è che le varie sottospecie di ape (Apis mellifica), hanno un differente concetto di lontano e vicino, o meglio dell’energia da spendere per raggiungere la meta. Questo può non sorprendere, visto che, abitando in contesti ambientali differenti, hanno pressioni selettive altrettanto differenti. Le sottospecie di montagna, come ad esempio Apis mellifica carnica, hanno un concetto di lontano più prossimo al nido rispetto a quelle di pianura come Apis mellifica ligustica, passando dalla danza circolare a quella ad otto già intorno ai 30 m, quando le altre lo fanno dopo i 70. La transizione vicino/lontano dà origine a figurazioni della danza relativa di forma intermedia. La figura 9 ci dà un esempio di tale fenomeno, che può avvenire secondo una transizione a ∞ (infinito) oppure a “falce”, tra la circolare e quella ad otto.
An interesting fact is that the various subspecies of honeybee (Apis mellifera) have different concepts of near and far, or rather of the energy required to reach a destination. This may not be surprising, given that, inhabiting different environmental contexts, they face different selective pressures. Mountain subspecies, such as Apis mellifera carnica, have a concept of near that is closer to the nest than lowland subspecies such as Apis mellifera ligustica, switching from the circular dance to the figure-eight dance already at around 30 m, while the others do so after 70 m. The near/far transition gives rise to figures of the relative dance of intermediate shape. Figure 9 provides an example of this phenomenon, which can occur according to an ∞ (infinity) or “sickle” transition between the circular and figure-eight dances.
The results of von Frisch’s work are so astonishing that they were initially met with disbelief; indeed, they were received cautiously by the scientific community, and many voices expressed disagreement. Today, however, we know he was correct and that those dances were the words of a language he understood firsthand. He achieved this through an evolutionary, comparative, and descriptive approach, conducting experiments in nature and fully applying the methods of ethology. The world was forced to accept that an animal other than humans (and a humble insect at that) could communicate information symbolically (A. Manning, 1979).
Credits
Author: N. Emilio Baldaccini, Former Professor of Ethology and Conservation of Zoocenotic Resources at the University of Pisa. He has published over 300 scientific papers in national and international journals. Actively engaged in scientific education, he is also a co-author of academic textbooks on Ethology, General and Systematic Zoology, and Comparative Anatomy.
Translated by Maria Antonietta Sessa
