Some science behind the scenes

Frequency of a bee’s hum

The frequency of the hum that we hear from a bee or any insect is due to the beats of its wings.  The sound is actually the result of the bee vibrating its flight muscles, and this can be achieved while the muscles are decoupled from the wings— so they can hum without flying or moving their wings, a feature known in bees but not in other insects. This is especially pronounced in bumblebees, as they must warm up their bodies considerably to get airborne at low ambient temperatures.

A bee flying has varying beats but in various studies the figure is about 150 to 200 beats per second or 150 to 200 Hz. This as we can see is well within the acoustic range.

Even in cooler weather or hovering flight rather than flight that moves the bee forward, although the wing beat does change, it is still audible. Wingbeat frequencies for the same breed of honey bee can vary from about 250 Hz down to 190 Hz [see The Journal of Experimental Biology:
"Honeybee flight metabolic rate: does it depend upon air temperature?"] There is also a genetic element "Africanized" honey bees (the so-called "killer bees") tend to have higher wingbeat frequencies in general than European honey bees.

A honey bee in the hive is normally resting and its wing beats are less.  A hive is often relatively quiet.  The bees are still beating their wings, because honey bees beat their wings to fan the gathered honey and help the water in it to evaporate thus helping it keep.  Once the water has gone they then cap the cells with wax.  So a bee is always busy and always using its wings, but clearly it uses them less in the hive than outside.  On further investigation, however, it appears that when fanning, a bee brings the frequency of its hum down to about 190 Hz. A drone beats its wings at about the same rate. 

Bees Healing Bees  - Valerie Solheim, Ph.D.

This suggests that 190HZ was the natural frequency level of the hive prior to swarming. Based on the above reference, a probable frequency range appears to be between 150-190Hz. Wenner ‘s sound recordings for the hive come in at 250Hz. Given the variances possible, a sound range between approximately 150-250Hz seems reasonable. I brought my brood hive recording to Professor Chang at the University of Colorado School of Music for an explanation of the sound. Professor Chang determined that the sound was an “E3 about 165 Hz with a variance that goes down a perfect fourth and up around a half step”.

The next question might be to ask if other parts or members of the hive are producing sound of a lower frequency, the brood for example, or the bees in the super, or bees during hibernation in winter.

Bees Healing Bees  - Valerie Solheim, Ph.D.

The frequency of bees changes throughout the day, the season, during hibernation, flows, requeening, etc, etc. As Linton observed,

…I would like to record the sound of honey bees in their hive. The sound they make varies over the course of a day and over the course of a season. It is affected by many factors, such as the presence or absence of a healthy queen, diseases, food supply, temperature, etc. Thus, the information, if analyzed in real time, could provide a quick indication of problems within the honey bee colony. For starters, I would like to record 30 seconds of audio every hour, indefinitely. I expect that once I have determined the bees’ patterns of sound, that much less data would be adequate, possibly 10 or 15 seconds of audio every 4 hours might be enough.

This would be overkill, as Linton later deduced. There exists a fundamental or natural frequency range for a healthy hive regardless of the time of year. What changes is the range of related tones around the natural frequency.

So what Valerie found in her studies was that although there is a fundamental frequency many other frequencies were present.  Scientists studying the frequencies tend to measure this fundamental frequency, using it to identify when a colony is sick or about to swarm or is angry.  But the other frequencies may be key in our context.

Valerie found that the brood box seemed to produce some particularly soothing effects…………

Bees Healing Bees  - Valerie Solheim, Ph.D.

The recording made from the brood box produced a continuous band of sound with sympathetic overtones. The brood box recording gave the most consistent and satisfying frequency output..

She also found that a bee produces sound from its tummy when it is communicating with other bees during foraging and other activities.

Bees Healing Bees  - Valerie Solheim, Ph.D.

The elasticity of the bee’s abdomen, growing with nectar and water and shrinking when unloaded in the hive, is attributed to collagen molecules which help tissues withstand stretching. ….Kruszelnicki suggests that the behaviour of bees oscillating their wings against their abdomen plays a role in communication and navigation.

Throughout her stay inside the nest, the recruiting forager produced sounds. During sound production, her folded wings vibrated dorsoventrally over her abdomen and she attracted the attention of follower bees who positioned their antennae closely around her body.

Bees also demonstrate an extraordinary sensitivity to vibrational frequencies

Recruiting foragers actually use several different mechanisms to communicate with other bees  - sound, smell, vision, thermal sense, and tactile sense.  If you think other animals and insects cannot talk because they don’t have language, you need to think again.  A bee has quite a highly developed communication capability.  They use coded signals of some complexity to communicate.

James Nieh - Professor and Vice Chair; Section of Ecology, Behavior and Evolution, UCSD

Stingless bees are an excellent model for the evolution of animal language because they possess the widest diversity of species and communication strategies, including the ability to acoustically encode the distance and height of food sources. Moreover, some species may use functionally referential communication.      For example foragers of the stingless bee, Melipona panamica, can communicate the three-dimensional location of food sources. To achieve this, foragers use a combination of mechanisms, including potential encoding of distance and height through sound pulses produced inside the nest.

The number of bees in a hive can vary throughout the year, and according to the space available to them to produce comb, but a commercial hive in summer can contain well over 60,000 bees.


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