Honey Bee Biology
Honey Bee Biology - December 2013
How Bees Measure Distance to a Food Source:
New Scientific Research
Von Frisch (1967) proposed a dance language where bees indicate the direction and distance to food sources with waggle dances performed in the hive (for locations roughly greater than 100 meters from the hive; a meter is a little longer than a yard). In performing the waggle dance, the bee runs on the comb in a squashed figure-eight pattern where the intersection of the loops is compressed into a straight run segment. After the straight run, the bee turns left or right returning to the straight run. During the straight run, the bee waggles, or vibrates, her abdomen from side to side.
The way the bees indicate the direction to the source can be inferred from several indicators: the position of the sun, the light polarization pattern across the sky, landmarks, and maybe magnetic fields (for references see Esch and Burns, 1996). Particularly for the sun position, researchers can use that information to predict the direction the bee is indicating in her dance.
The researcher can use the tempo of the dance to figure out the distance to the food source by measuring, for example, the number of dance cycles (loops) per 15 seconds or the time spent in the straight-run part of the dance. A slower dance tempo indicates greater distances, or correspondingly fewer dance cycles (per 15 seconds) or more time spent in the straight run.
How the bees actually determine the distance, at one time, may have seemed clear, but upon closer examination, not so. Originally, the experiments conducted by von Frisch in 1967 (and others) published in his monumental work, The Dance Language and Orientation of Bees, led to the energy hypothesis, where bees determine distances by the energy they consume during flight, specifically on the outbound flight to the food source. However a close examination of the older experimental results show support for the energy hypothesis was rather weak, as reviewed by Esch and Burns (1996) of the original German papers. For example, here is the “mountain slope” experiment that was conducted by Heran and Wanke. With a hive placed on a steep mountain slope, foragers collected sugar water at up-slope and down-slope feeders. Since the bees traveling up-slope were empty on their outbound flight (flying up) and loaded coming home, flying down with a “push” from gravity, they should expend less energy (determined from the tempo of their dances). The bees traveling down-slope were empty on their outbound flight (flying down) and loaded coming home, flying up working against the “push” from gravity. They should indicate more energy consumed through their dance tempo. Only 2 of 7 experiments showed the bees seem to measure the expended energy on the outbound flight. The remaining 5 experiments were claimed to have wind interference.
A repetition of the essence of the mountain experiment showed different results. With a hive placed 158 meters from a 50-meter tall building, bees collected sugar water at a location at the base of the building and on top of the building. Bees foraging at the top of the building needed more energy for that trip, which was even calculated (1.522 Joules) compared to bees flying horizontally to the base of the building (1.032 Joules). Yet from the tempo of the dances of the two groups (top versus base of the building), no difference was detected (Esch and Burns, 1996), casting considerable doubt on the energy hypothesis.