QuestionHouse cricket
Can Crickets Tell the Temperature? Dolbear's Law Explained
Yes, roughly: crickets chirp faster when it is warm and slower when it is cool, so their song can be used as a simple thermometer. For the snowy tree cricket of North America, counting the chirps in 15 seconds and adding 40 gives the temperature in degrees Fahrenheit, usually to within a few degrees.
Contents
How to use a cricket as a thermometer
The best-known method is called Dolbear’s law. It works best with the snowy tree cricket (Oecanthus fultoni), a pale green tree cricket whose males sing in a steady, rhythmic chorus on summer and autumn nights. Its song is often nicknamed the sound of a quiet summer night, and it is used on many film soundtracks.
| What to count | What to do | Result |
|---|---|---|
| Chirps in 15 seconds | Add 40 | Temperature in °F |
| Chirps in 8 seconds | Add 5 | Temperature in °C |
| Chirps in 1 minute (N) | 50 + (N − 40) ÷ 4 | Temperature in °F (Dolbear’s original form) |
| Chirps in 1 minute (N) | (N + 30) ÷ 7 | Temperature in °C (approximate) |
For example, if a snowy tree cricket chirps 28 times in 15 seconds, the formula gives 28 + 40 = 68 °F, which is 20 °C. These formulas use round numbers so they are easy to remember. They are estimates, not precise measurements, and some versions count for 13 or 14 seconds instead of 15.
Who was Dolbear?
Amos Dolbear was an American physicist and inventor who taught at Tufts College in Massachusetts. In 1897 he published a short article called “The Cricket as a Thermometer” in the journal The American Naturalist, giving his formula for estimating the temperature from the chirp rate. He did not name the species he listened to, but later scientists concluded it was the snowy tree cricket.
Dolbear was not the first to notice the link. In 1881, Margarette W. Brooks of Salem, Massachusetts, described the relationship between chirps and temperature in a letter to Popular Science Monthly. Dolbear apparently did not know of her earlier observation, but his formula became the famous one.
There was also confusion about the cricket’s name. For decades it was called Oecanthus niveus, until the American entomologist Thomas J. Walker showed in 1962 that the snowy tree cricket was a separate species. It was named Oecanthus fultoni in honor of the cricket expert Bentley B. Fulton.
Why do crickets chirp faster in the heat?
Crickets are cold-blooded, or ectothermic, which means their body temperature follows that of their surroundings. The chemical reactions that power their muscles and the nerve signals that control them both run faster when the insect is warmer.
A male cricket chirps by rubbing a toothed file on one front wing against a scraper on the other, a process explained in why do crickets chirp. The rhythm of this movement is set by a small network of nerve cells in the cricket’s body, and like a clock that runs faster in the warmth, it speeds up as the temperature rises. In cool weather, the song slows down; below about 10–13 °C (50–55 °F) many crickets hardly sing at all.
What about the females? Studies on field crickets have found that a female’s preference for song rhythm also shifts with temperature, so on a warm night she prefers faster songs. This “temperature coupling” means males and females of the same species still recognize each other whatever the weather.
How accurate is Dolbear’s law?
For the snowy tree cricket, the formula is often accurate to within a few degrees, which is surprisingly good for an insect. Several things can make it less reliable:
- Where the cricket sits. A cricket’s body is at the temperature of its own perch, which may be warmer or cooler than the air where you stand, for example on a sunny wall or in a cool hedge.
- Different species. Each species has its own chirp rate. The western snowy tree cricket (Oecanthus rileyi) and other tree crickets chirp at different rates, and populations of the snowy tree cricket west of the Great Plains also chirp faster.
- Field and house crickets. Common field crickets and the house cricket chirp less regularly. Their rate also depends on age, size, whether they have recently mated and whether other males are nearby.
- Outside the normal range. The formula only works while crickets are singing normally. It cannot work below the temperature at which crickets fall silent, and it breaks down at high temperatures.
Math teachers sometimes use Dolbear’s law as an example of a model with limits: taken literally, it predicts thousands of chirps per minute at temperatures no cricket could survive.
Other insects that keep time with the temperature
The link between temperature and rhythm is not unique to crickets. Katydids, grasshoppers, cicadas and fireflies also tend to sing or flash faster in warm weather, because all are cold-blooded. Grasshoppers make their sound in a different way, usually by rubbing a hind leg against a wing, as described in grasshopper vs cricket.
The snowy tree cricket stands out because so many males sing together in near-perfect unison, which makes their shared rhythm easy to count. On a warm evening in late summer, a chorus of snowy tree crickets in North America can be a surprisingly good guide to the temperature, at least to within a few degrees.
Can you try it yourself?
Yes, and it makes a simple outdoor science activity. Listen on a calm evening for a steady, pulsing chorus of pale green tree crickets in shrubs and trees, then count chirps for 15 seconds with a watch, add 40 and compare the result with a thermometer. Repeating the count several times on different nights shows how closely the insects follow the weather, and where the formula starts to go wrong.
Frequently asked questions
How do you tell the temperature from cricket chirps?
For the snowy tree cricket, count the chirps in 15 seconds and add 40 to get the temperature in degrees Fahrenheit. For Celsius, count the chirps in 8 seconds and add 5. Both are rough estimates.
Does Dolbear's law work for all crickets?
No. The formula was based on the snowy tree cricket of North America, which sings in a steady rhythm. Other crickets, including house and field crickets, chirp at different rates and are affected by age, mating and other factors.
Who discovered that crickets chirp faster in the heat?
The physicist Amos Dolbear published the best-known formula in 1897 in an article called The Cricket as a Thermometer. Margarette W. Brooks had already described the link in a letter to Popular Science Monthly in 1881.
Why do crickets chirp faster when it is hot?
Crickets are cold-blooded, so their body temperature follows their surroundings. Warmth speeds up the chemical reactions in their muscles and nerves, so the wing movements that make each chirp become faster.
At what temperature do crickets stop chirping?
It varies by species, but most crickets sing little or not at all when it is colder than about 10–13 °C (50–55 °F). On very hot days some species also become less active.
Sources and further reading
- Dolbear, A. E., "The cricket as a thermometer", The American Naturalist 31 (1897)
- Walker, T. J. and Moore, T. E., Singing Insects of North America (University of Florida), "Snowy tree cricket, Oecanthus fultoni"
- Encyclopaedia Britannica, "Cricket"
Cite this page
“Can Crickets Tell the Temperature? Dolbear's Law Explained.” Animal Atlas, https://animals.bigworldlist.com/questions/can-crickets-tell-the-temperature/.
