Fascinating. Thank you for posting it.
I've also read that tiny sensitive microphones in a corn field can tell when crops get thirsty (useful for agricultural water conservation) by picking up minute high-frequency "popping" sounds made by capillaries. Click for reference.

While seeking a link to the above, I also ran across this item from last year's Better Homes and Gardens:
    "Every living organism makes noise, but most of us aren't sensitive to it," says Bernie Krause, coauthor of Wild Soundscapes: Discovering the Voice of the Natural World.
    Kids (and most adults) are surprised to learn that ants sing. Krause suggests placing an inexpensive lavaliere microphone, plugged into a tape recorder, in the dirt over a carpenter ant hole and recording sounds. The ants' communication sounds like high-pitched, rhythmical chirps.

Who knew you could learn so much about the world just by listening? (Mama told me, but I didn't listen...)