Naturalists have long known that queens inside the hive emit two kinds of sound, called "tooting" and "quacking." A close analysis of these sounds and the circumstances of their emission now provides the strongest evidence that bees use sound to convey specific messages.
Tooting is the regal identification of a virgin queen soon after she has emerged from the cell in which she developed. A hive cannot tolerate more than one queen at a time. In a hive that lacks a queen several queen-bearing cells develop simultaneously in a comb, but one matures earlier than the others. Once this queen has emerged, has hardened and has become steady on her legs, she proceeds to visit other queen cells, tear them open and sting to death their potential but not yet mature queens. Often, however, the worker bees do not allow her to dispose of all her potential rivals in this way; they bar her from some of the cells. She then begins to toot and continues to do so day and night, perhaps for a week or more. Her tooting rises in intensity and sometimes can be heard more than 10 feet from the hive.
There's a video of piping queens after the jump.
Meanwhile the maturing queen bees still in cells try to get out in their turn. The worker bees hold them back, however; as fast as one of them opens the cap of her cell the workers push it back in place and glue it shut. Thereupon the imprisoned queens also start to pipe, but in a different pattern and at a lower tone than the free queen. The workers let out some of these quackers, but only one at a time. The reigning queen and the newly released rival then battle until one is killed. Sometimes the series of fights between the survivor and the new rivals goes on until only one queen is left. This survivor, still a virgin, then flies away from the hive to mate successively with several drones (on the wing) and returns to begin laying eggs.
All this has been studied in hives set up for detailed observation. The tooting and the quacking have also been recorded and (9. analyzed spectrographically). The pattern of the first turns out to be a long toot (lasting one second) followed by several shorter toots. Its fundamental frequency is 500 cycles per second, and this is overlaid with overtones that are varied considerably in emphasis, just as they are in human speech [see "Attention and the Perception of Speech," by Donald E. Broadbent; SCIENTIFIC AMERICAN, April, 1962]. The quack differs from the toot in two ways: it has a lower fundamental frequency and it begins with short sounds instead of a drawn-out one.
Do the tooting and the quacking say different things to the bees? We investigated this question with a set of controlled experiments. First we recorded the tooting of a free, reigning queen in its hive. Analysis with the sound spectrograph showed that this tooting put the major emphasis on the third harmonic. We therefore mimicked this harmonic with an oscillator and played it in the same tooting pattern (a long toot followed by several short ones) in a second hive that contained a free queen and a caged one. To each sounding of the artificial toots the caged queen almost invariably responded by quacking (10. see illustrations). We then tried varying the frequency of the tone, while keeping the long-toot-short-toot pattern constant. Within a wide frequency range (600 to 2,000 cycles per second) the change in frequency seemed to make little difference: the queen still responded with quacks as long as the typical pattern of toots was the same. On the other hand, when we played the quacking pattern, the caged queen did not respond at all.
There is not much doubt that the tooting and the quacking represent certain messages. What do the messages say, and what functions do they serve? A reasonable working hypothesis is that (1) the tooting announces the presence of a free queen in the hive, (2) the quacking reports the presence of challengers ready and yearning to be freed from their cells and (3) all this information guides the worker bees. One queen tooting and others quacking means that there is just one free queen, and a quacker (but not more than one) may be released to challenge her. This procedure will result in the rapid killing off of all but one of the contenders, but that may be to the good; it will enable the hive to settle down quickly to a peaceful regime. Occasionally, however, particularly in the spring, a virgin queen or an older egg-laying queen may leave the hive permanently, taking along half of the adult bees, in the phenomenon called swarming. In the swarming season, therefore, it is essential to have a queen in reserve when the free queen departs; a quacking queen may represent survival for the hive and is not to be released until the swarm has left.
Here's a video that demonstrates both sounds (start at the 6:35 mark):