How tree crickets use leaves to amplify mating calls

The tiny insects employ them as loudspeakers to announce that they are looking for a date

The insects follow three rules to

How do you find a mate when you are just two centimetres in size and there aren’t very many who match your profile?

An old trick is to draw attention to yourself by creating a lot of noise. But the tiny tree crickets have taken this a step further: they amplify their mating calls using loudspeakers that they themselves build using leaves.

Now, scientists have discovered that the loudspeakers they make are almost maximally optimised for the purpose at hand: transform any given leaf into the best ‘amplifier’ it could be.

A contraption

When these ingenious insects rub their wings together to generate sound, they also engineer a biological contraption known as a ‘baffle,’ which increases its volume.

They do this by cutting a neat hole near the centre of a leaf, adjusting themselves within the hole, and flapping their wings against the leaf surface, thereby using it as a megaphone.

A group of scientists from the United Kingdom and India studied how these insects (male Oecanthus henryi ) selected the leaves and cut the holes. The findings were published recently in the journal eLife .

The team observed that the insects always followed three design rules for making the baffle: use the largest available leaf; make a hole the size of the wings and place the wings at the centre; and make the hole as close to the centre of the leaf as possible.

They invariably select the best leaf and modify it appropriately, all in a single attempt.

“Brain size is often conflated with intelligence. We ought to look at insects a bit harder and even what we think is stereotyped may not be so. Making baffles is almost certainly an inherited behaviour....and not really studied that much. When given a choice of two leaves, they always pick the bigger. They exercise what we call material selectivity. When it’s hard to find large leaves, they don’t waste time on the small leaves that make poor baffles,” writes Natasha Mhatre, who was part of the team at the University of Bristol, that conducted the study and the first author of the paper.

In an email to The Hindu , Rittik Deb of the Centre for Ecological Sciences, Indian Institute of Science, and co-author of the paper, says: “The discovery that tree crickets can optimise acoustic baffles means we are just about beginning to tap into under-appreciated intelligence of insects.”