The Indian Express (Delhi Edition)
They’ve got the vibe
Insects rely on vibrations to make melodies, with high notes and low, often to communicate with each other
DECADES AGO in Mumbai, I remember watching a group of treehoppers lined up on a plant stem, looking like a queue of little thorns. These sap-sucking insects come in various shapes and sizes and colours. There are over 3,000 species worldwide. Recently, I came across these little insects again in Ed Yong’s remarkable book, An Immense World (2022) and they blew me away. Apparently, these silent little insects actually sing and very melodically too, but we can’t hear their songs unless we use what is called a vibrometer, a device which converts vibrations into audible sound. Apparently, the treehoppers cause vibrations on the stem or leaf they’re on by rapidly contracting their abdomen muscles, and these vibrations travel across the surface and up the legs of recipient treehoppers, which, may in turn, respond. The sound, a deep rumble, has been described as a purr, but more lion than pussycat and unlike anything you would expect from an insect. And it’s not only treehoppers that use vibrations to communicate, it’s estimated some 200,000 species of insects do. Treehopper hits are haunting, sometimes mesmerising and may sound more like birds, apes and even musical instruments.
Travelling through the air, sound waves lose energy quickly and so have to be focused in a narrow range of frequencies. Hence, it’s the high-pitched chirps we normally hear from insects. But travelling through a solid, flat medium, they retain their energy, which gives the insects the chance to widen their bandwidth, including high notes and low, making melodies in the bargain. Baby treehoppers will produce a chorus of vibrations when they fear a predator and their Mama may respond by producing vibrations which tell them to be quiet lest they attract even more unwelcome attention. Gentlemen treehoppers emit a whine, followed by sharp pulses and if there’s an interested lady around, she’ll respond with a hum. He’ll figure out where she is and come closer, and whine and pulse again, and she’ll hum again, until they meet up. Of course, matters get complicated if there is a rival gent around — who will try to jam the first gentleman’s calls by interrupting him — rather like what happens in TV debates, I suppose. As treehoppers can gather together in large numbers on a plant, the chorus of calls can make it sound like Goa’s Mapusa market on Fridays!
Acacia ants — which live in the bullhorn acacia, feast on the nectar they produce and the honeydew produced by aphids — will sense the vibrations of any creature, such as a goat attacking the leaves and swarm out in ferocious defence. Some of the other insects using vibrations include grasshoppers, which apparently sound like revving chainsaws, and cicadas, which sound like cows. Spiders use web vibrations to inform them of when dinner has arrived — and even what’s on the menu and the serving size that day. One species even pre-tunes its web to be receptive to a particular item on the menu — say a small fly — and, of course, gentlemen spiders wooing their giant ladies often play the harp on the web strings to lull them into a more romantic, woozy (and less cannibalistic) frame of mind.
Though I haven’t tried it yet, apparently you can hear insects sing even without a vibrometer. Back in 1949, a scientist placed a leafhopper on a blade of grass and put the blade of grass in a testtube and then listened. He was a musician, too, and he transcribed what he heard into musical notes. Apparently you can do this with a simple clip on microphone and speaker. It really is mind-boggling to think that there may be some 200,000 insect species out there all making their own music — like some giant philharmonic orchestra. All we hear is the buzzing of bees and flies, the wailing of mosquitoes and the tinnitus-like shrillness of the cicada in forests. They’ve got the vibes and we’re probably missing out on a concert of a lifetime.
The vibrations of grasshoppers sound like revving chainsaws, while those of cicadas, sound like cows