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12th January 2009, 13:50

Find the Temperature Using Crickets
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Why and How of Cricket Chirping

You have no doubt heard crickets chirping away in the grass and bushes. The male cricket chirps at regular intervals in order to attract female crickets, ward off predators, or establish territory. He creates the cricket chirping sound by rubbing one of his wings on a hard rigid structure located on its other wing.

You can use these cricket chirps as a way to determine the temperature. But first, a little lesson on why this works:
Cricket Metabolism

Like all insects, crickets are cold blooded. This means that unlike you and me (warm blooded creatures) a cricket produces little or no body heat of its own. Instead, a cricket’s body temperature tends to match the temperature of its surroundings

Because the metabolism of an insect is proportional to its body temperature, if it is too cold the cricket cannot even move. As the temperature of its environment warms, the cricket's body also becomes warmer. Its metabolism increases and the insect can move faster.

You have probably witnessed this increase in insect metabolism as the temperature increases. For example, ants will run must faster when on a hot sunny sidewalk as compared to when it is cool.
Calculating Cricket Temperature

What does all this cold-blooded-temperature-of-the-environment stuff have to do with finding the temperature using crickets? Plenty. You see, the warmer the ambient temperature of the crickets surroundings, the warmer the cricket. And the warmer crickets increased metabolism allows it to chirp faster.

In 1898 Amos Dolbear noticed that warmer crickets seemed to chirp faster. Dolbear made a detailed study of cricket chirp rates based on the temperature of the crickets environment and came up with the cricket chirping temperature formula known as Dolbears Law:

T = 50 + (N - 40) / 4

T = temperature in degrees Fahrenheit.
N = number of chirps per minute.

For those of you who cannot remember your elementary school math, here is the wordy version of the same cricket temperature formula:

Count the number of chirps the cricket makes in 1 minute (60 seconds)
Subtract 40 from this number.
Divide the result by 4
Add 50.

The result of this calculation is close to the temperature of the environment the cricket is in. For example, if the cricket chirps 120 times in one minute then the temperature is about 50 + (120 - 40)/4 = 70 degrees.

If you are working in degrees Celsius here is the Dolbears Law formula for degrees C:
T = 10 + (N - 40) / 7

A simplification of Dolbears Law can sometimes be found listed as something like:

Temperature = Number of chirps in 13 seconds + 40

Which seems to closely agree with the more complicated formula Amos Dolbear came up with.
When Determining Temperature Using Crickets

It is important to note that the cricket chirp temperature formula is based on the temperature of the cricket, which is not necessarily the temperature of where you are. Be aware that the temperature of the grass or bushes close to the ground where the cricket is may be quite different than the temperature several feet off the ground.

Another factor that must be considered is that Amos Dolbear came up with his revolutionary cricket temperature formula while experimenting with Snowy Tree Crickets. Other crickets may give varying results based on the cricket species and age.

Estimating the temperature using cricket chirps is a good approximation of the temperature. Give it a try and amaze your friends!

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