The Song of the Bees: Lightning's Audible Alert

I just came across a phrase I had never heard before, thanks to a video that explains the phenomenon very clearly: the song of the bees. In the mountains, that is the name given to a sound that announces lightning. Anything that turns an audio signal into life-saving information gets my attention, so I started digging. What I found has absolutely nothing to do with insects.

A buzz without a single insect

What French-speaking climbers call the song of the bees is a corona discharge, also known as the corona effect. It belongs to the same family of phenomena as St. Elmo's fire, described by sailors for centuries at the tops of ship masts.

The mechanism comes down to a few numbers. In fair weather, the electric field at ground level runs around 150 volts per meter. Under a thundercloud, it climbs to 15,000 or 20,000 volts per meter. That is still far below the roughly 2.6 million volts per meter needed to ionize air, except that terrain cheats: any sharp point concentrates the field lines and can amplify the local value by several hundred times. A rock ridge, an ice axe blade, the tip of a trekking pole, the crampons strapped to a pack. The threshold gets crossed at the tip of the point, and nowhere else. The air starts snapping in micro discharges.

How a spark becomes a sound

Here is the part that fascinated me. Each micro discharge abruptly heats a tiny bubble of air, which expands and then collapses. That is an acoustic pulse, a micro explosion, exactly the way a lightning bolt produces thunder but on a scale thousands of times smaller. A single discharge would be an imperceptible click. There are hundreds per second, spread across every sharp edge in the vicinity, and they fire in completely random order.

That randomness is what builds the texture. Electrical engineers know it well, since it is the same effect that makes high-voltage power lines sizzle in damp weather. One important difference, though: on an AC line, ions shuttle back and forth at the grid frequency and add a distinctive low hum. In the mountains, a thunderstorm's electric field does not oscillate at 60 hertz. That hum disappears, leaving nothing but the shower of random pulses. Hence the resemblance to a swarm rather than a transformer. Our ears, for lack of anything better, file the crackle under the closest biological category available.

A phrase born in a novel

The image did not come out of a laboratory but out of alpine literature. Roger Frison-Roche planted it in "Premier de cordée," published in 1941 and known in English as "First on the Rope," where two guides recognize the buzzing and understand too late what it means. The expression entered the professional vocabulary and never left.

It deserves a moment of attention. Very few trade expressions are built purely on an act of listening, and fewer still have survived eighty years without distortion. It is a sonic description so accurate that physics never had to correct it, even though the law describing the onset threshold of corona discharge had already been formulated by F. W. Peek back in the 1910s and 1920s.

What researchers have only just seen

The strangest part is that this phenomenon, familiar to generations of mountaineers, had never been directly observed in the field. That changed in February 2026, when a team at Penn State published the first outdoor measurements of corona discharges in Geophysical Research Letters, captured with a telescope coupled to an ultraviolet-sensitive camera.

The targets were not ice axes but trees, under thunderstorms along the East Coast of the United States. On a single sweetgum, the researchers logged 859 signals in an hour and a half. Each discharge lasted between 0.13 and 3.33 seconds, and more importantly, they hopped from one leaf to another in a completely sporadic pattern, sometimes returning to the same leaf. That visual description is an exact match for what the ear interprets as a swarm in motion. Nothing in the paper addresses the acoustics, but the geometry of the phenomenon is finally documented.

A warning, yes, but the last one

One point needs to be clear. This sound is not an early warning signal. The French Ministry of the Interior puts it bluntly: by the time you hear the buzzing characteristic of the corona effect, the ambient electric field is already intense, and you need to get off the ridge immediately. In other words, the ear arrives at the very end of the chain, after the sky, the clouds, and the barometer. It confirms a danger, it does not announce one.

That takes nothing away from its value. It is the only sign of imminent lightning that reaches us through hearing, and the only one that still works in fog, with your back turned, or with your eyes closed.

The missing sound in my library

Let me close with an admission, because it seems more honest than pretending otherwise. I could not find a single scientific recording of this phenomenon in the mountains, no published spectral analysis, no level measurement. Every piece of hard acoustic data available comes from high-voltage power lines, measured in labs or test corridors. What exists on the mountain side is testimony.

That is a startling gap for a sound documented across generations. It puts the song of the bees in the same category as the sound of the northern lights, long dismissed as a storyteller's legend for lack of a clean recording. And it makes the phenomenon a textbook case of geophony, those sounds produced by the planet itself, here without a single living organism involved. Which, for something named after an insect, is not without irony. Real bees have their own acoustic file, since certain flowers respond to their buzzing.

One practical difficulty probably explains this documentary silence: to capture the sound, you have to be standing exactly where you must not stay. Have you ever heard the bees in the mountains, and did you have the reflex, or the madness, to hit record?