Pine beetle chirps are too quiet for humans to hear, but they play an important role in beetle courtship.
"Upon finding a suitable tree, the female pine beetle will begin constructing a gallery of tunnels inside the bark. She then emits pheromones to attract a male for mating. A male pine beetle arrives quickly and finds the female inside her gallery. The male then gives a courtship chirp to win her over. To make the sound, the male rubs a rasp-like file on the top of his abdomen against the inside of the hard wing covering. The male guards the gallery from other would-be suitors. If another male enters, a violent wrestling match ensues, and both males emit wild, aggressive chirps.
It's important to remember that pine beetle chirps are so quiet that, without tools like a highly sensitive microphone placed inside the tree's bark, we are unable to hear them."
"Mountain Pine Bark Beetle Chirps," written by Eric Ott, read by Caroline Kurtz.
(Broadcast: Fieldnotes, 8/24/14 & 8/25/14)