Q: Is it true that some crickets can tell us the temperature? If so, how does it work and what are the Bay Area species to listen for? —Eddie, Albany
A: I was recently in the Amazon, high up in an observation tower overlooking the canopy and as the tropical morning progressed, the cicadas suddenly started singing…loudly. And our guide said, “It must be getting hot now.” We sure didn’t need those insects to tell us that! But with the cicadas, temperature acts just like an on-off switch. When it reached about 77 degrees, they started singing.
However, throughout North America (except for a few states), we have our very own so-called thermometer cricket—the snowy tree cricket (Oecanthus fultoni). Way back in 1897 a professor at Tufts University figured out a formula to determine the ambient air temperature based on the number of chirps this cricket makes per minute. It’s pretty darn accurate. When west of the Rockies, you count the number of chirps during 12.5 seconds and then add the number 38 to get the temperature in Fahrenheit.
I bet that most of you, like me, have heard these snowy tree crickets in the evening every year beginning around midsummer and on into the fall. They’re widespread in the Bay Area, and while no one’s ever surveyed the regional snowy population, entomologists suspect they’re common in some areas. While they’re mostly herbivorous, they also eat aphids, making them a gardener’s friend. What we hear are the males singing to attract females. Assuming the crooning Casanovas succeed, the females—which look very similar to the males—then lay eggs in the bark of trees or shrubs and even potted garden plants. Those eggs hatch the following spring and very slowly mature into adult tree crickets; by midsummer they are ready to mate.
As the environment around the cricket heats up, the cricket’s own metabolic processes increase in frequency and speed. Among those temperature-dependent processes are chemical reactions that control the muscle contractions involved in vocalizations or stridulations (the rubbing together of body parts to make sounds). When it gets warm enough, the male crickets are able to start singing. They raise their wings to a 45-degree angle and draw the scraper of one wing across the furrows on the underside of the other wing. It is like running your finger along the teeth of a comb and presto—a loud sound from a small insect. This activity increases in direct proportion to the temperature.
There are three other tree cricket (Oecanthus) species, and field crickets, in the Bay Area whose chirping can also be counted, but the snowy tree cricket is much more precise. However, these insects can probably only sing between about 48 and 100 degrees Fahrenheit. So outside of that range, you’ll have to rely on a thermometer.