Step outside on a Long Island evening in late August and the air itself seems to pulse. The sound comes from everywhere and nowhere: the hedges, the foundation plantings, the strip of unmowed grass along the fence. Thousands of small musicians are playing at once, and most of us long ago filed the sound under summer and stopped hearing it. But the chorus is carrying information. Somewhere in it, a pale green cricket is keeping time so faithfully that you can read the temperature by its song.

Who is out there singing

Start with who is making the sound, because it is stranger than it seems. The singers are male, nearly all of them, and they are not singing in any vocal sense. A cricket's instrument is its own body: one wing carries a row of fine ridges like a file, the other a hardened edge like a scraper, and drawing one across the other at speed produces the chirp. The wings themselves, raised and angled, act as the amplifier. The technical word is stridulation, but what it amounts to is a violin the player was born wearing. The song is courtship, each species with its own signature, so that a female in the dark can find her own kind by ear alone.

Listen for a few minutes and the wall of sound separates into layers. Low in the grass and along the pavement cracks is the field cricket, the classic hearty chirper, dark and glossy, singing day and night. In the shrubs and low branches is a different music: a silvery, even, continuous pulse, softer-edged, which is the tree crickets. And after full dark, from high in the oaks, comes the harsh, rhythmic rasp of the katydid, scratching out the three-beat call it is named for: ka-ty-did. Separate the layers once and you will never again hear the night as a single sound.

Why heat sets the tempo

Here is the part that turns the yard into an instrument panel. Crickets are ectotherms: they do not maintain a body temperature, they take on the temperature of the air around them. Every process inside them, nerve signal and muscle contraction alike, is chemistry, and chemistry runs faster warm than cold. Each chirp is a burst of muscle contractions, so on a warm night the whole apparatus fires quicker and the song speeds up. On a cool night it slows, deepens, turns sluggish and drowsy, and near the edge of a cold snap it grows halting. The cricket is not choosing a tempo. The temperature is choosing it.

An idea from 1896 you can test tonight

People had noticed the pattern for as long as anyone had slept with the windows open, but it took a physicist to write it down as arithmetic. In 1896, Amos Dolbear, a physics professor, published a short paper titled The Cricket as a Thermometer, putting numbers to the relationship between chirp rate and air temperature. Boiled down to its handiest form, the rule is this: count the chirps in fourteen seconds, add forty, and you land close to the temperature in degrees Fahrenheit.

The rule works best on one performer in particular: the snowy tree cricket, the pale, even-tempered singer of the shrub layer. Its chirps are mellow, evenly spaced and easy to count, and on many nights every snowy tree cricket in a yard falls into sync, the whole neighborhood pulsing on one beat. Field crickets make less reliable instruments; their rate wanders with age, hunger and the presence of rivals. So the trick is to find the even, silvery pulse, the song that sounds less like chirping and more like a soft ticking laid over the dark, and count that one.

Then test it. Stand outside tonight, count fourteen seconds of chirps, add forty, and check the number against a real thermometer. Most nights you will land within a few degrees, and when you are off, remember that the cricket is reporting conditions where it actually sits, in the still air of a hedge, not at the airport where the official reading lives. You may find, unsettlingly, that the cricket and your porch disagree with the forecast and that the cricket is right.

The urgency in the sound

There is a reason the chorus peaks now, in the back half of August, and it is worth knowing because it changes how the sound lands. Most of the yard's singers began as eggs laid last year, hatched in spring, and spent the summer growing through stages, wingless and silent. Only in the second half of summer do they reach adulthood and, with it, the wings that are their instrument. Singing is what the adult stage is for. The concert you are hearing is the year's whole generation arriving at its purpose at once, with a season that is already closing.

From here the arc bends down. Through September the song thins and slows: cooler nights drag the tempo, and one by one the players drop out. The first hard frost ends the concert outright. What survives the winter is what started it, eggs tucked into soil and plant stems, holding until the ground warms again. The chorus outside your window is not background. It is a finale, played nightly, by musicians who will not see October.

Listening as a practice

The counting trick is a party fact, and it is also something better: it is a reason to stand still in your own yard for one full minute doing nothing but listening. That is rarer than it sounds. Most of what we know about the places we live comes through a windshield or a weather app, secondhand and summarized. Counting chirps is firsthand. It puts you outside, after dark, paying the kind of attention that turns a wall of noise into individual voices, and a yard into a place with inhabitants.

And attention compounds. Stand out there long enough to count fourteen seconds and you will notice other things: which corner of the yard holds the day's warmth longest, where the katydids actually are, how the sound changes after rain. The naturalist's secret was never the Latin names. It is staying put until the ordinary admits it was never ordinary.

So take the fact and use it. Fourteen seconds, add forty. The thermometer was outside your window the whole time, running without batteries, accurate enough to argue with. And in February, when the yard has gone silent, you will know what the silence is made of: the eggs are in the ground, the next orchestra already seated, waiting through the cold for the heat that will set the tempo again.