Baffled: Crickets use tools to boost their song

06 March 2018

Interview with

Natasha Mhatre, University of Toronto at Scarborough

TREE CRICKET

A tree cricket calling from a baffle

Crickets have been shown to be able to create and use tools for the first time. The insects can amplify their mating calls by creating 'baffles' from modified leaves, getting a volume increase of up to 400%. Chris Smith heard from Natasha Mhatre, who has been investigating how...

Natasha - These creatures are called Tree Crickets. They’re about a centimetre in length - they’re really beautiful. Most of us see crickets from the pet store which look kind of brown and a bit cockroach-like. Tree crickets are really pretty: they have translucent wings, they have long antennae - those small green things - a there’s tree cricket species more or less all over the world. The ones that we’re working on come from India.

All tree crickets do with really amazing thing which is that they sing to attract mates. They put up their wings, which are resonant, rub them together and set them into vibration and produce really beautiful tonal sounds; that’s what you can hear on a summer nights. These sounds are heard by the females who can use them to identify males of their own species from other males, and find the males.These tree crickets also do this amazing other thing which is that they make an aid that helps them be louder than they would be on their own.

Chris - Really; what do they do?

Natasha - They make a things called a baffle. A baffle is, for a tree cricket, very simply a hole cut in a leaf that they sing from. They place their wings directly against this hole and sing from inside it, and this makes them louder.

Chris - Is that a bit like you see people walking around in the old days on Hollywood sets with a megaphone, which was basically a cone with the end chopped off and they shout into it? Is it sort of doing something similar, they’re creating an amplifier from a leaf to make themselves louder?

Natasha - It’s a bit similar. I’ll try and explain the physics as simply as I can. If you can imagine the wings as a board that’s vibrating back and forth. Every time the board moves forward, it produces high pressure in front of it and behind it it produces low pressure, and this is essentially what sound is - its changes in pressure. But what will happen is that the high pressure and the low pressure will meet at the edge of the board, and when they meet with each other they’ll cancel each other out. This is something we call acoustic short-circuiting.

Now the smaller the board is, the more of the sound that’s produced is short-circuited. If you can somehow prevent these two, high pressure and the low pressure from meeting each other, then you can prevent acoustic short-circuiting. And that’s essentially what’s happening when a cricket puts itself in the hole in the leaf. What happens is that the front face of the wing is, effectively, acoustically separated from the back face of the wing and they end up being louder.

Chris - How does the cricket find the leaf and the hole in the first place?

Natasha - Ah, there’s a big secret in that. One of the things that we did was to see whether there are different baffle designs. It turned out, if you model this, you find that some baffles perform a lot better than others. And the baffle that performs the best is made with the largest leaf with a hole that’s exactly the size of wings and placed dead centre in the leaf.

Chris - Right. So next question then: given that that’s the optimal solution what proportion of the crickets actually opt for that?

Natasha - Well, it depends on the situation. But when we did an experiment in which we gave 19 crickets the choice between a small leaf which wouldn’t make such a good baffle and a large leaf which would make a great baffle, 15 crickets made a baffle and every single one of them made a baffle in the large leaf. They made a baffle in the large leaf with the optimally sized hole and they got pretty close to the centre, so all of the crickets seemed to know how to make an optimal baffle.

Chris - Now, given that crickets sing at night, they’re therefore able to work out the size of a leaf, discriminate between leaves that are bigger and smaller. Then having worked out the size of the leaf and made a choice, they’re then working out where the middle is. How on earth are they doing that?

Natasha - Yeah, they are doing that. We have no idea. There may be different ways in which they’re doing this: one is to walk along the edge of the leaf, the other is use these really beautiful long antennae that they have to touch the edges of the leaf to see if the edges are further away on one leaf than another other and using themselves to centre in the middle of the leaf. But, to be honest, the answer is we don’t know how they’re doing it yet.

Chris - How much louder is the baffled cricket compared with a non-baffled cricket? In other words, what sort of an advantage - a sonic advantage do they gain through doing this?

Natasha - A cricket that’s in an optimal baffle will be four times as loud as a cricket that’s on its own.

Chris - This completely changes our view of insects, doesn’t it? Because we mostly think of insects as sort of dumb automatons but here you’ve got very simple organisms, they’re making a sequence of decisions informed by their own measurements in order to achieve an outcome and that’s really quite striking.

Natasha - Absolutely. It has been a long-held view that invertebrates are stereotyped, and vertebrates, mammals, birds, etc. are extremely clever. We’ve been having to change this view. I think one of the first things that really jolted this was when they found that octopuses can make tools. They were making all sorts of tools. Now, if you think about it a little bit an octopus is a mollusk, it’s the same as a snail. So really, we can’t hold onto this idea any more that invertebrates are simpler animals. They’re just different from us and we’re absolutely going to have to look very closely at how insects behave in order to be able to appreciate what’s going on that’s not immediately apparent on the surface.


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