Sunday, April 27, 2003		Nature

The dance code of the bees
Nutan Shukla

THE foraging behaviour of bees has been the subject of exciting research, particularly by the Austrian scientist Prof. Karl von Frisch in the first quarter of the previous century. It was he who first discovered that these insects are able to convey the precise information to their fellow bees about the source of food, whether it is nectar or pollen. Professor Frisch found that the basis for their communication system is their dance language that had remained an enigma until he decoded it in 1923.

Bees perform two kinds of dances - the round dance, used to convey that the food source is not far away from the hive; and the waggle dance to convey the opposite, i.e. the source is far from the hive. As soon as any worker finds the food source, it returns to the nest to tell about his discovery by a ritual dance, each movement of which gives precise information to the fellow bees.

Professor Frisch, who spent about 50 years studying the complex world of bees with unparalleled devotion, concluded that if the food source is within 110 yards of the hive, the discoverer will perform a round dance on the vertical face of the comb within the hive. Meanwhile, other workers in the hive will encircle the informer and communicate by rubbing their antennae against his. After dancing for a while, the dancer stops and regurgitates a small amount of nectar collected from the source, perhaps as a proof or to give his fellows the idea about the flowers involved.

In the second case, where the food source is further from the hive the discoverer tells about it, its distance, location and the direction by performing a different and far more complex dance in which it dances in a ‘figure of eight’ pattern, with two loops separated from one another by a straight line running down the middle. If the line in the middle is straight up the comb, it means that the food is in the direction of the sun; if vertically down then the food is in the opposite direction to the sun. If it is at an angle of 60 degrees to the left of the vertical, the food source is in a direction of 60 degrees to the left of the direction of the sun. Thus the direction of the sun is indicated as vertically upwards and a line of dance at an angle to the vertical shows food at the same angle from the sun’s direction.

As the dance goes on, the performer waggles its abdomen in a rhythmic sequence of movements. The rhythm and the time consumed by the body movement, coupled with the intensity of the low-frequency humming sound produced, conveys the precise message that permits the other members of the hive to fly without any hesitation straight to the food source.

Scientists say the message provided by the dancing bee is remarkably informative, incorporating all the factors of importance in aerial navigation, such as wind conditions, temperature and position of the sun. It is a rare example of a descriptive language among animals. The identity of the flowers concerned is usually indicated by the odour of regurgitated nectar, but in the case of odourless flowers or flowers without a pronounced fragrance, an indication is given by releasing pheromones from the glands situated on the posterior part of the dancing bee’s abdomen. It was believed for a very long time that bees depend entirely on their eyesight but now it has been established that pheromones also feature in their behaviour to a large extent.

Now it is an established fact that the rhythm of the dance conveys information about the distance between the hive and the food source. As the distance increases, the number of circuits decrease. For instance, if the source is 100 m away then the dancer will carry out between 36 to 40 circuits; for a source situated at a distance of 500 m there will be 24 circuits, and if the distance is 1500 m the number of circuits gets reduced to 16. Now the question arises: How do these creatures determine distance? Scientists say that they apparently measure it by the amount of effort put in to cover it.

When the dance is being performed, a humming sound is produced from the varying degrees of vibrations originating in the stomach muscles, while the wings are kept in a resting position. Studies conducted on bee behaviour have further revealed that if the distance increases, the bee will penetrate further into the hive to dance.

The ability of bees to navigate is also remarkable and for this they take the help of the sun, using a kind of internal compass. These insects are also gifted with the ability of seeing ultraviolet light and can also respond to polarised light. Owing to this quality they are able to navigate even in cloudy weather.

Bees are highly industrious creatures, travelling long distances to gather food. Usually, they forage within a radius of just about two km around the hive, but many workers can go up to 6 km and in rare cases, a distance of up to 10 km may be covered. In an experiment, a hive was placed in the middle of an area devoid of plants. It was observed that some of the bees belonging to that hive travelled as far as 13 km in search of food. Another experiment conducted on genera Euplusia, Euplaema and Euglossa revealed that some of these insects inhabiting the tropical forests of Costa Rica, flew as far as 23 km searching for food, indicating that they are capable of considerable feats of navigation.