The first land animals to communicate using sound were, in all probability, insects. Insect acoustics is an exciting field of study that addresses questions such as how insects use their sounds to communicate, how different are the 'languages' or the 'words' that various insects use and how acoustic signals are interpreted by them. An expert in this discipline is Prof. Rohini Balakrishnan from the Center for Ecological Sciences, Indian Institute of Science, Bangalore.
In a recently published book, Insect hearing, Prof. Balakrishnan reviews the latest developments in the field of insect acoustic communication within the larger context of acoustics and hearing in her chapter – Behavioral Ecology of Insect Acoustic Communication. In a captivating (yet highly informative) manner, the professor discusses how various insects use their sounds to communicate and choose mates, the strategies they employ to ensure that their signals don’t get mixed up, and much more.
The book, Insect hearing, is one in the Springer Handbooks’ series on auditory research and has different volumes which deal with a variety of topics like human auditory perception, the evolution of hearing, acoustic communication, sonar and more. These are compilations of contemporary research, each of which is written by an authority on the topic and thus considered excellent reference material by researchers worldwide.
But why, in the first place, are insect sounds so important? Well, for starters, many insects use their sounds mostly to find themselves a mate. For animals that move around together, exaggerated visual displays (such as the peacock that fans out its feathers) could help. But, what if one has no idea where, in the vast wilderness of the forest, to find a potential mate? Insects like the grasshoppers, cicadas and crickets believe in simply calling out loud to let the females know- Hey, I’m here. And thus begins the drama.
It is, of course, not always as simple as only singing out an interest. Females are naturally enamoured by males that have found a perfect spot to lay their eggs and with good local access to nutritional provisions. The males know this and they fight for it– there are even vocal duels that lead to brawls. Some species are known to observe rituals such as ‘nuptial gifting’– the male secretes and stores a sack of nutritive juices on its body for its prospective partner. In such instances, it is the females that get competitive and may even fight over males! In other instances, there are even examples of duets, where the male calls out seeking a female and the female responds in an– I’m here, come to me– fashion.
Courtship conversations are, of course, very specific to the category an insect belongs to. But, these conversations are not only heard by prospective mates, but also by predators lurking around in anticipation of a good meal. To make matters complex, there are so many different kinds of insects inhabiting the same space within a forest. How is a potential mate expected to differentiate between sounds in this loud cacophony? More thought-provoking, however, is the question– How do researchers even attempt to figure all of this out?
Prof. Balakrishnan’s studies and experiments include trips into the woods at dusk and into the night (that’s when most insects prefer to begin their dalliances) to capture sounds for their research. They later process the collected insect babble and use them to reconstruct the acoustic world in an attempt to perceive how the forest would sound to various animal listeners. The expeditions are not at all dreary, as one might imagine. The Professor recollects one instance where several of her students –‘fielders’– were surrounding a tree with a giant singing cricket on the trunk, disturbing it so it glides down, and everyone trying to ‘catch’ it, then getting down on hands and knees and rummaging through the fallen foliage in the hunt for this animal, with a weak torchlight! “It was a different but equally exciting form of ‘cricket’”, she recalls.
About the book chapter
Chapter Title: Behavioral Ecology of Insect Acoustic Communication
Book Title: Insect Hearing