Years ago, when I was a kid, I heard about a Frank Lutz study in which snowy tree crickets could be used as a thermometer by counting their chirping rate, which, because they are poikilotherms, varies with the ambient temperature. At the time I thought that was interesting, but a little irrelevant, since I had a thermometer. But we don’t always have a thermometer when we’re, say, camping, so a few years ago I had my Biology class make a thermometer by going outside, recording the temperature, and counting the chirps per minute of our local crickets. I don’t know the cricket species, but it is a common one in late summer when school starts. Here are their data, compiled to show a good polynomial fit. The linear equation, upper left, is also a good fit at r = 0.96.