You can hear them from twelve feet away. Rhythmic grating sounds from within a dead white pine tree in our neighbor’s yard. Sarah heard them first on her early morning walk. We returned later in the day, but the munchers had fallen silent. It seems that their appetite is keenest at dawn.
Here are the sounds, with a labeled spectrogram of the same sound. I suspect that the crunching sounds are coming from large Cerambycid larvae (long-horned beetles). The hairy woodpecker that was diligently extracting them from under the bark would know for sure. Beetle larvae that live under bark can thrive on seemingly indigestible wood using a combination of detoxifying enzymes produced by their own guts and through use of cellulose-digesting enzymes that the insects derive from the fungi that live inside the wood. This is a bit like digesting moldy cornflakes by harnessing the power of the mold. A clever strategy, but one that I’ll leave to the beetles.
Spectrogram (time moves left to right; frequency (pitch) is on the vertical axis):