Crickets do not rub their legs together. Only males chirp. And you can estimate the temperature just by counting. Here is everything behind that sound.
Cricket chirping is produced by stridulation, rubbing specialized structures on the forewings together. A file on one wing and a scraper on the other combine to produce the familiar sound. In the species we typically hear singing, males produce several distinct songs: a loud calling song to attract distant females, a quieter courtship song used nearby, and an aggressive song for rival males. Many crickets are most active after dark, though the pattern varies by species, season, and temperature. Because crickets are ectothermic, their chirp rate generally rises and falls with the air temperature around them.
In 1897 physicist Amos Dolbear published a mathematical relationship between chirp rate and temperature, later simplified into a shortcut: count chirps for about fourteen seconds, add forty, and get an estimate in Fahrenheit. But the history behind Dolbear’s Law is messier than the name suggests. Margarette W. Brooks had published experiments on the same relationship in 1881, and she herself referred to an even earlier observation by someone identified only as W.G.B. Daniel and Mom trace the anatomy, the behavior, the temperature formula, and the layered attribution history behind one of science’s more charming discoveries.
DanielMom, why do crickets chirp all night? I was lying in bed last night listening to them, and I could not figure out why they never seem to stop.
MomDaniel, the short answer is that they are trying to find a mate. But the longer answer involves wing anatomy, cold blood, and the fact that in 1897, a physicist worked out that you can estimate the outside temperature just by counting cricket chirps.
DanielReally? You can tell the temperature from cricket chirps?
MomYes, there is even a rule for estimating the temperature from cricket chirps. Count for a few seconds, do a tiny bit of arithmetic, and you can get surprisingly close. It traces back to a physicist who published a formula more than a century ago.
DanielHmm. First, how do crickets actually make that sound? Is it by rubbing their legs together?
MomGood guess. Almost everyone thinks that. But no, crickets make the sound by rubbing their wings together. One wing has a ridged edge called a file, the other has a part called a scraper. When the cricket raises its wings and draws one across the other, the scraper runs along the ridges and produces the chirping sound.
MomThe process is called stridulation.
DanielInteresting. So, the chirp is actually a wing sound, not a leg sound.
MomIn the cricket species we usually hear singing, it is the males making those songs. A male's loud calling song is essentially a broadcast, mainly advertising himself to females that are listening. It is not random noise. It is communication.
DanielOkay, but why at night specifically?
MomMany cricket species are most active after dark, and their calling is controlled partly by daily rhythms, as well as temperature and other conditions. But it is not a universal rule, you know. Some crickets call during the day too, and calling patterns can vary with species, season, and temperature.
DanielSo, the nighttime chorus I hear is real, but not every cricket follows the same schedule.
MomAnd what is remarkable is that a single male cricket actually produces several distinct types of sound, rather than just one. There is a loud calling song to attract females from a distance, a quieter courtship song used when a female is nearby, and an aggressive song directed at rival males.
MomResearchers have identified these as functionally different communications, not just variations of the same chirp.
DanielSo what sounds like one cricket doing one thing is actually a cricket with a whole vocabulary.
MomYes, a small vocabulary, but a real one. And now, let's talk about the temperature. Crickets are ectothermic, what people often call cold-blooded, so their body temperature and activity are strongly affected by the temperature around them. As temperature rises, the biological processes controlling their wing movements generally speed up, so the chirp rate rises too.
DanielSo, a cricket on a hot night generally chirps faster than one on a cool night because its body is running at a different rate.
MomConsistently enough that in 1897, an American physicist named Amos Dolbear, published a short paper called The Cricket as a Thermometer. He gave a mathematical relationship between chirp rate and temperature. Today, there is a famous shortcut based on Dolbear's law.
MomCount the chirps for about 14 seconds and add 40 to estimate the temperature in Fahrenheit.
DanielSo you are just counting and adding, no instrument, just a cricket and 14 seconds.
MomBut there is an important catch. The shortcut works especially well with the snowy tree cricket, which is sometimes called the thermometer cricket. Different cricket species chirp at different rates, so you cannot necessarily count any cricket you happen to hear and expect the same formula to work perfectly.
DanielWas Dolder the first person to notice that temperature changes cricket chirping?
MomNo, and this is where the history gets interesting. In 1881, 16 years before Dolder's paper, a woman named Margarette W. Brooks published a letter in Popular Science Monthly describing experiments on how temperature affected cricket chirping. And Brooks herself referred to an even earlier newspaper observation by someone identified only by the initials W.G.B. So, even Margarette Brooks was following a clue somebody else had noticed.
MomExactly. Dolder deserves credit for publishing the mathematical relationship that became famous, but the observation behind it had already been circulating. Science is often less like one person having a sudden idea and more like people noticing, testing, measuring, and building on what came before.
DanielSo calling it Dolder's Law tells us who published the famous formula, not necessarily who first noticed the phenomenon.
MomAnd next time you are lying awake listening to them, you will know what that sound actually is. A male cricket raising his wings and drawing a scraper across a file, trying to be heard above everything else in the dark. Sending out a signal, not knowing if anyone is listening.
DanielThat is actually a very beautiful way to think about crickets.
MomAnd crickets belong to an incredibly ancient branch of insects. Their ancestors were here long before there were humans lying awake listening to them. So, Daniel, what is one thing you are taking with you today?
DanielOh boy, so many fascinating things! About cricket! So, let's see what I remember. Crickets make their sound by rubbing their wings together, not their legs, a process called stridulation. In the species we usually hear singing, males use different songs for different jobs.
DanielA calling song to attract females, a courtship song when a female is nearby, and an aggressive song for rival males. Let's not forget that many crickets call at night, although different species follow different schedules. Because crickets are ectothermic, temperature affects how quickly they chirp.
DanielIn 1897, Amos Dolbear published a mathematical relationship between chirp rate and temperature. And today, a shortcut based on Dolbear's law lets you estimate the temperature by counting chirps. But people had noticed the connection before Dolbear. Margarette Brooks experimented with it in 1881, and even she referred to an earlier observation.
MomA thermometer, a broadcasting station, and a nighttime musician with several different songs, all in one small insect.
DanielI am going to count cricket chirps every summer night for the rest of my life.
Mom Margarette Brooks would be very pleased to hear that.
