I’m Singin’ in the Rain! Oh no, now I’m dead. The perils of Auditory Communication in Insects

As I mentioned yesterday, we are going to spend a few days looking at the different ways insects communicate.  Today we will venture into the world of auditory communication.

Crickets probably represent the most often thought of insect when it comes to insect sound production.  If you have ever been out in a field on a warm summer evening you can’t hear a darn thing besides those little buggers going at it.  And that’s the point of their sounds, is to “go at it.”  The calling sound we hear is a mating call.  Contrary to what many thing, the sound is not produced by the male cricket rubbing its two legs together, but rather by rubbing its wings together. While there are some insect species which rub the leg against the adjacent forewing (most forward originating wing) this is not true of crickets and katydids.  Being science-type people, we have to give this activity a fancy name and we have dubbed it “Stridulation”…and it was good.  Stridulation is simply the rubbing together of two specific body parts in order to produce a sound.  These two parts are called the file and the scrapper.  The scrapper has “teeth” on it and the file is smoother, though it may still have some bumps.  The sound is produced similarly to how you might rub a pencil over a comb.

YouTube: Cricket Chirping Video

Cool as this may be (well, cool to us nerds) this does have its drawbacks.  Not only do we hear those crickets singin’ away, but so do their predators.  In some areas of the country there is a species of fly which is able to tune into that specific sound the cricket makes, find it and lay a larvae on it.  The larvae then gets inside the cricket and starts to chomp down on the crickets innards, hanging out in its muscle tissue.  The cricket is still alive while the larvae is in there, though it’s not going to have a good few days.  The larvae depletes the crickets needed nutrients and even though the cricket is still eating, it is losing some of what it needs from that food to the parasite.

Not only does that cricket need to worry about predators and parasitoids finding it, it also needs to worry about how much energy it’s using.  Yes, auditory communication has its perks; signals can be sent out quickly, it goes in a variety of directions and information is passed on with or without a direct line of sight to the intended target.  If this was, for example, visual communication, the intended recipient would need to be right in the line of sight to see whatever display was being made, but not with auditory.  However, there are some drawbacks.  It’s horribly expensive and highly inefficient.  A cricket can use around 1/2 of its energy stores in a given evening all with a measly 1% efficiency level.  Yikes!  Not only that, but this poor guy also has to contend with wind, rain, plants and other things that might distort or block the sound from getting where it needs to be.  Being a cricket isn’t so easy, is it?

Tachinid fly pupa on cricket host: Formed after the larvae progressed through its life cycle, exited the cricket and formed a pupa, still attached to its hosts belly.

Given these potential problems, most insects have taken to using substrates (surfaces/substances) as a means to transmit the sounds they are producing.  This typically takes the form of tapping on bark, leaves, stems, etc.  This is especially effective when we’re talking about insects which live on the same plant and need to pass info around.

Once the insect makes its mating call, the auditory fun doesn’t stop there!  Some insects need special sounds to be made before and even during mating in order for the sweet, sweet love to be made.  Take this Noctuid moth for example.  At the end of this video we hear an ultrasonic sound that the male makes while it’s attempting and then succeeding in mating with the female.  If he doesn’t make that sound, she will leave.  She’s a picky lady!

The ability to produce sound is believed to be a rather recent evolutionary adaptation that insects have developed.  I say “recent” as in, compared to other methods that arose with the earliest arthropods 400 million years ago.  Insects and their arthropod relatives have been on this planet a very long time and will continue to populate it long after the zombiepocalypse has doomed us all.  And when that day arrives, somewhere there will be a cricket screaming its wings off trying to find a lady for the night.

So how would you fare during the Zombiepocalypse?  I’ve got my boomstick at the ready.

For more info about what I touched on above check out the following links and resources:

Stridulation

Tachinid Parasitoids Effect on Crickets

Noctuid Mating Sound Article

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