Take a walk through the woods and youâ€™ll be treated to birds and other animals making their characteristic sounds. But thereâ€™s a hidden world of sound among insects, frogs and other creatures who communicate by vibration. I’m Jim Metzner, and this is the Pulse of the Planet.
ambience: Male thornbug â€œadvertisement signals,â€ female thornbug duet
Weâ€™re listening to a duet between a male and female thornbug, an insect, a species of treehopper, that lives most of its life on the stem of a sapling. A thornbug produces a sound by vibrating its abdomen, transmitting that vibration through the stem of the plant that it lives on. Weâ€™re hearing these vibrations with the help of a sensitive microphone. Still – itâ€™s a big sound for a tiny insect.
â€œSo, weâ€™re used to hearing small things make high pitched sounds and big things make very low pitched sounds. Because for airborne sound, very small animals arenâ€™t very efficient at producing low frequency sounds that can travel very far through the atmosphere.â€
Rex Cocroft is an assistant professor of biology at the University of Missouri.
â€œThe physics of the signal production are very different for plant born vibrations, and so, in fact, even a really small animal can produce a very low frequency signal. So, the relationship between size and frequency that we are so used to in our acoustic world is really no longer there once we move to the vibrational world. So it is very startling sometimes to see a very small insect, that is producing a sound, that is so low pitched, that when we play it as an airborne sound, you have to imagine that this has to be some huge animal. â€œ
â€œMost insects are very good at detecting vibration, and treehoppers – they almost certainly have vibration receptors in their legs and these are what allow them to pick up the vibrations traveling through the plant.â€
Pulse of the Planet is presented by DuPont, bringing you the miracles of science for 200 years, with additional support provided by the National Science Foundation.