Weather Bug

Have you ever gone camping while the chirping sound of crickets lulled you to sleep? Not only do these small invertebrates produce a pleasant sound on a warm summer evening, but they also have the ability to act as natural thermometers. The species Oecanthus fultoni has an amazing thermometric ability.

When the male cricket rubs one wing against the other, he produces the chirping sound. The frequency of this sound is directly proportional to temperature where the cricket is located.

Every day folk can calculate the outside temperature in degrees Fahrenheit simply by counting the number of chirps in 14 seconds, and adding 40.

The University of California has a more sophisticated formula for those that wish to calculate the temperature more precisely. “Count the chirps per minute, subtract 40, divide by 4, add 50 and that will be the temperature in degrees Fahrenheit.” Yet another study defines the equation as the number of chirps in 15 seconds, added to 37.”

So why are there all these variations? One possible reason is that the actual function is not supposed to be linear.

Figure 1: Linear fit of the number of chirps per 13s versus outside temperature.

Figure 2: Exponential fit of the number of chirps per 13s versus outside temperature.

A group of scientists in the early in the 20^th century gathered the data points on these graphs. They prove that the equation for determining the temperature from a cricket chirp is not linear. All the variations in the proposed equations are therefore only due to the differences in the best line fit of the actual curve.

The equation for the line in figure 2 is:

Chirps per 13 seconds = 5.63 x 10¹⁰ exp[–(6290 K) / T ]

This equation does have a couple of setbacks to it. First of all, it may scare the general public. Apart from this, the real question is who would actually care to memorize it? Even more so, what percentage of the population would bring with them calculators to a campsite?

While it may be a quick and easy way to determine the outside temperature, the simple linear equations are only useful for campers who do not need a precise measurement.