From the June 1949 issue of Natural History, the magazine of the American Museum of Natural History (which is archived here) comes a handy reference guide for telling the temperature based on the number of cricket chirps you hear for two given cricket species, and a third – Mr. X, the mystery cricket.
“Know the insect orchestra, and you can clock the temperature,” promises Mr. Hallenbeck. Mr. X is secretive and shy, so his identity remains unknown, but this cricket is the best insect thermometer I have ever found,” Mr. Hallenbeck says.
Of additional interest to UFO buffs: These insect observations were made in 1949 in Roswell, New Mexico, two years after the famous crash. Chances are, Mr. X is a Hoplosphyrum boreale and not a gray alien … but you never know.
I recommend the whole article for its charm. There’s also a lovely chart of katydid calls by temperature, spelled out in capital and lowercase letter-Ks.