What science tells us

The flower a bee makes vibrate

Some bees have an astonishing way of collecting pollen.

They grip a flower and rapidly activate their flight muscles without taking off. The vibrations transmitted to the flower help eject pollen from anthers that release it through tiny pores.

This is buzz pollination.

In Solanum rostratum, researchers studied this mechanism with a laser vibrometer, which measures movement without touching the flower. A dominant vibration of 300 Hz applied at the base retained its frequency as it travelled through the tissues. Its amplitude, however, could change dramatically: in some anthers and petals it exceeded 400% of the input amplitude.

The flower is therefore not merely being shaken. Its geometry and tissues influence the way the vibration travels, weakens or is amplified.

Between bee and flower, pollination becomes a story of mechanics as well.

When a leaf becomes a sensor

Does a plant know it is being eaten?

The wording is deliberately provocative, because it could suggest that a plant “hears” or “thinks” like an animal. That is not what experiments show. What they reveal is more precise and, in its own way, just as remarkable: a plant can respond to certain mechanical vibrations produced when an herbivore feeds on it.

In 2014, researchers worked with Arabidopsis thaliana. They recorded the vibrations produced by caterpillar chewing and then played those vibrations back to plants that had not yet been attacked. After this exposure, the plants mounted stronger chemical defence responses when they were later attacked.

The most interesting point is selectivity. The plants did not respond in the same way to every movement: chewing vibrations did not have the same effect as wind vibrations or the vibrational song of an insect.

This distinction matters. It lets us preserve the wonder without turning genuine mechanical sensitivity into an imaginary ability.

A network of threads

The spider that senses its web

A little farther away, between two branches, another vibration tells a very different story.

For a spider, a web is not only a trap. It is also a transmission medium.

The movements of prey, those of a potential mate and certain disturbances in the environment do not create identical signals. In web-building spiders, sensory organs distributed along the legs detect deformations and vibrations travelling through the silk.

The geometry of the web, its tension and the properties of different silks themselves influence how this information circulates. Some spiders also use particular vibrations during courtship, allowing a male to announce his presence without being mistaken for prey.

We see a web. The spider also inhabits everything that travels through its threads.

A plant network for communication

The secret conversations of stems

A stem is not merely a support for leaves and flowers. For many insects it can also serve as a transmission route.

True bugs, leafhoppers and other small arthropods produce signals that travel through plants. They tremble, tap, stridulate or vibrate parts of their bodies. These messages can help them find a mate, recognise another member of their species, defend a resource or signal danger.

In some leafhoppers, courtship becomes a genuine vibrational duet. The male sends a signal, the female replies, and the exchange changes as the male approaches. In Empoasca vitis, researchers have shown that the timing of the duet changes between the localisation phase and courtship itself.

More surprisingly, in the grapevine leafhopper Scaphoideus titanus, partners have managed to establish a duet between two nearby leaves that were not touching and were separated by a gap of a few centimetres. Vibrations in one leaf can move the air and excite the neighbouring leaf, which then becomes a vibrating substrate in turn.

A bush that seems silent to us can therefore carry an entire traffic of mechanical messages.

A message through several channels

Inside the hive, the comb carries the message too

The honeybee waggle dance is one of the best-known forms of animal behaviour. A forager returning to the hive can provide other bees with information about the direction and distance of a resource.

But the dance is not merely visual. In the darkness of the hive, bees use several channels at once: touch, air movements, odours, vibrations of the comb and close-range acoustic signals.

Laser vibrometry measurements have detected comb vibrations during the waggle phase mainly around 200 to 300 Hz. Their amplitude is extremely small, but it overlaps with the sensitivity thresholds of some bee mechanoreceptors.

Communication is therefore multimodal. No single sense tells the whole story.

What looks to us like a dance is, to the bees following it, also a scene of touch, smell, movement and vibration.

Before birth

The egg that recognises an approaching snake

In the tropical forests of Central America, the red-eyed treefrog, Agalychnis callidryas, lays its eggs on leaves above water.

When snakes or certain wasps attack an egg clutch, the predator’s movements produce vibrations. The embryos can then hatch earlier than usual, drop into the water and escape the attack.

Heavy rain, however, can also shake the clutch. Hatching at every vibration would be costly: a tadpole that leaves its egg too early is more vulnerable in the water.

Experiments therefore show that embryos do not simply respond to “a lot of vibration”. They use several cues, including vibration duration, intervals between events, frequency content and amplitude. The timing pattern of an attack is not the same as that of rainfall.

Even before seeing the outside world, an embryo can make a life-saving decision from mechanical information.

Beneath our feet

The elephant that receives the world through the ground

Elephants are famous for very low-frequency vocalisations. Some of the energy generated by these calls and by certain body movements can also travel through the ground as seismic waves.

For several decades, researchers have been studying how elephants might produce, transmit and detect these signals. Proposed anatomical and behavioural mechanisms include sensitivity in the feet and the conduction of vibrations towards structures of the ear.

Not everything has been resolved: the effective range, the importance of this channel in different contexts and its interaction with airborne hearing remain active areas of research.

But one point is well established: the ground is not an immobile backdrop. It too can carry information.

For a large animal travelling over long distances, listening to the world can therefore mean, in part, listening to what passes beneath its feet.

When wings speak

Wings that choose silence

Birds add another variation to this story.

In owls, several features of the wings help make flight remarkably quiet: comb-like serrations along the leading edge of some feathers, fringes, a soft velvety surface and large wings that allow relatively slow flight.

The precise contribution of each of these structures is still being studied. Recent work has shown, in particular, that the “velvet” on some feathers greatly reduces friction noise when feathers slide against one another.

In another bird, by contrast, wing noise has become a message.

The Australian crested pigeon, Ocyphaps lophotes, has a highly modified eighth primary flight feather. It produces a characteristic note with each wingbeat. During a rapid take-off in response to danger, the tempo of the signal increases; playback experiments have shown that other pigeons use this wing sound as alarm information.

In one case, evolution favoured discretion. In the other, it turned wing movement into a signal.

In both cases, movement becomes information.

And what about us?

Vibrations, oscillations and rhythms

We belong to the same physical world, but one word needs to be used carefully here.

Our vocal folds vibrate when we speak: that is a mechanical vibration. Our eardrum vibrates in response to sound waves. Some tissues can also be set into vibration.

By contrast, heartbeat, breathing, nervous-system activity and the sleep–wake cycle are better described as rhythms or biological oscillations. They change over time, sometimes very regularly, but that does not mean they all correspond to a single mechanical vibration.

Our bodies are therefore crossed by many different timescales, from extremely rapid phenomena to circadian rhythms close to twenty-four hours.

Life is not tied to one particular frequency. It consists of many rhythms, oscillations and vibrations.

Back to metal

Why a bell contains several notes

A bell is not simply an object that “rings at one frequency”. When struck, its wall deforms according to several natural modes at the same time. Each mode has its own frequency, amplitude and decay rate.

In a tuned European bell, five main partials are traditionally described: the hum, prime, tierce, quint and nominal. They do not necessarily form a perfect harmonic series like that of an ideal string. Their combination gives a bell its distinctive richness, at once stable and constantly changing.

The material matters, of course, but so do the shape, thickness, profile, diameter and the way the metal has been worked. Over centuries, bell founders developed an extraordinarily refined empirical understanding of these relationships, long before vibrometers and spectral analysis could measure them.

A metal instrument such as an Aum Drum belongs to a different family and has its own geometry. Yet it can evoke a bell because it too involves several modes of vibration, partials that persist for different lengths of time and a long decay.

What the ear perceives is therefore not a fixed note but a sound material that continues to change after the initial strike.

Heritage we can hear

When stone prolongs sound

A bell resonates by itself. A church transforms whatever sound is entrusted to it.

Large volumes, vaults, mineral surfaces, side chapels, pillars and the arrangement of spaces all affect how sound travels. In many historic religious buildings, reverberation times are long: sound persists after its source has stopped because its energy continues to reflect between surfaces.

This acoustic can magnify certain kinds of singing and blur speech. It varies enormously from one building to another according to size, materials, furnishings, occupancy and history.

There is no general evidence that cathedrals or abbeys were designed around a mysterious “sacred frequency”. The relationships between architecture, liturgy and music, however, are very real. Church acoustics are now a research field in their own right, and some researchers regard them as a dimension of heritage worth preserving alongside stone, stained glass and decoration.

Heritage is therefore not only what we can see. A place also has its own particular way of responding when a voice, an organ, a bell or simply a footstep sets it in motion.

A widespread idea

What about the famous “432 Hz”?

One sometimes encounters the claim that music tuned to 432 Hz is a “natural frequency”, supposedly closer to the body, water or the Earth, while the modern 440 Hz standard is artificial — or was even imposed in order to influence populations.

The history is both simpler and more interesting.

First, 432 Hz or 440 Hz is not the frequency of all the music. The number refers only to the chosen reference frequency for the A above middle C.

Second, there has never been one universal, immutable tuning standard handed down from Antiquity. Pitch standards varied for centuries according to place, period, ensemble and instrument.

Giuseppe Verdi did advocate a reference close to 432 Hz. His documented concerns were those of a musician: he wanted to curb the tendency for pitch to rise and to avoid excessive strain, particularly on singers’ voices. Recent historical research on his “A” does not attribute to him a theory of therapeutic or cosmic frequency.

As for 440 Hz, its history did not begin with a secret decision by the Nazi regime. In the United States, the music industry had already adopted it as a reference in 1925, followed by the American Standards Association in 1936. An international conference in London also selected 440 Hz in 1939. ISO later adopted it as a recommendation in 1955, before ISO 16 was published in 1975 and remains in force today.

None of this prevents anyone from preferring music tuned slightly lower. Two tunings can create different impressions.

But an aesthetic or sensory preference does not need to be turned into a hidden law of the Universe.

And perhaps this is where reality becomes even more beautiful: we do not need to invent a sacred frequency to discover a world that is extraordinarily rich in vibration.

Epilogue

Receiving a world larger than our senses

At the end of this journey, one simple idea remains.

It would be tempting to conclude that “everything is vibration”. But the phrase is too vague to teach us very much. A circadian rhythm, a sound wave, a vibration in a web, a cellular oscillation and a wingbeat are not all the same physical phenomenon.

What is true — and perhaps more beautiful — is that living things make use of an immense diversity of movements, waves, rhythms and signals.

A bee vibrates a flower. A plant alters its defences after certain chewing vibrations. A leafhopper converses through a stem. A spider receives the world through its web. A treefrog embryo analyses the shaking of its egg. An elephant can receive part of its information through the ground. An owl has evolved quiet wings while a pigeon has turned its wings into an alarm.

And we humans have learned to direct microphones, lasers, accelerometers and equations towards these phenomena so that we can perceive what our unaided senses would miss.

Wonder is therefore not reserved for what we cannot explain. It can also arise from what we come to understand more clearly.

What this inspires in the Knights of Astrée

Protecting what we cannot perceive as well

Caring for living things also begins by understanding that we do not all inhabit the same sensory world.

Where a human sees a yellow flower, a bee may encounter a structure it can set vibrating.

Where we notice a few almost transparent threads, a spider receives a network of information.

Where we hear only a beat of wings, another bird may perceive a warning.

Where an owl crosses the night almost silently, that silence itself tells a story of millions of years of adaptation.

Looking after an oasis of biodiversity therefore does not mean protecting only what is visible. It also means leaving room for quieter things: soils that transmit, stems that oscillate, webs stretched between blades of grass, insects that buzz and birds that communicate in ways other than song.

Receive. Protect. Pass on. Living things are already doing this all around us.

Sources and further reading

• Campanometry — the statistics of bells: the five principal partials of bells.
• Biomechanical properties of a buzz-pollinated flower: vibration transmission in Solanum rostratum.
• A Spider’s Vibration Landscape: vibration and spider webs.
• Acoustics of rubbing feathers: the role of feather velvet in reducing noise.
• Sounds of Modified Flight Feathers Reliably Signal Danger in a Pigeon.
• Recent historical work on “Verdi A”.
• National Bureau of Standards — history of the A=440 pitch standard.
• ISO 16:1975 — standard tuning frequency.
• Biotremology in arthropods: principles and uses of substrate-borne vibrations.
• Plants respond to leaf vibrations caused by insect herbivore chewing: defence responses in Arabidopsis.
• Inter-plant vibrational communication in a leafhopper insect: duets between nearby leaves without contact.
• The reproductive strategy and the vibrational duet of the leafhopper Empoasca vitis.
• Behaviour-locked signal analysis reveals weak 200–300 Hz comb vibrations during the honeybee waggle dance.
• Flexible information sampling in vibrational assessment of predation risk by red-eyed treefrog embryos.
• The Role of Vibration Amplitude in the Escape-Hatching Response of Red-Eyed Treefrog Embryos.
• Keeping an ear to the ground: seismic communication in elephants.
• Church acoustics: A state-of-the-art review after several decades of research.