Crickets: Nature's Thermometer

In 1897, a physics professor at Tufts University named Amos Dolbear spent time counting cricket chirps. He noticed the rate changed with the temperature. Being a physicist, he wrote down the numbers and looked for the relationship.

He published what he found in The American Naturalist. Count the number of cricket chirps in fifteen seconds. Add forty. The result is the temperature in Fahrenheit, within a couple of degrees. He named this observation after himself. Dolbear's Law is not named after an entomologist or a naturalist. It is named after a physicist who was paying attention to the wrong thing and found something real.

The formula works because crickets are ectotherms. Their body temperature tracks the air around them, and the processes that drive muscle contraction, the enzyme-catalyzed reactions that power each movement, run faster as temperature rises. A cricket chirp is a muscle event: two sets of ridged wings drawn across each other, one scraping the other to produce the sound. Warmer air, warmer muscles, faster enzyme reactions, more chirps per second. The relationship between temperature and chirp rate is linear within the range crickets are active, which is why a simple formula holds.

The species the formula applies most accurately to is the snowy tree cricket, Oecanthus fultoni, a pale, almost translucent insect that lives in shrubs and low trees. Its song is a steady, even trill rather than the raspy pulse of the field cricket most people picture. The regularity is what makes it countable, and countable is what made Dolbear's observation possible in the first place.

In late July, across most of the eastern United States, the first crickets of the season are audible at night. By August the sound fills every warm evening. It is easy to stop noticing it, the kind of background noise that becomes furniture. It is also a real-time temperature measurement, running continuously, broadcast at whatever volume the night requires.

The test is simple and takes fifteen seconds. Find a cricket, an open window will work. Count its chirps for fifteen seconds. Add forty. That is the temperature in Fahrenheit, give or take, reported by an organism whose metabolic relationship to heat was described by Amos Dolbear in 1897 and has not changed since.

He published that formula in a natural history journal and moved on. The cricket kept reporting.

Going outside on a warm late-summer night and standing still enough to count is a way to use your attention on something specific. The ambient sound that reads as background is a measurement. Rewyld exists for moments like this: when what the living world is doing and what you are actually paying attention to become the same thing.