The "Ear" of a Praying Mantis

Hi everyone!

It's common knowledge that insects make sounds; many species in the Order Orthoptera (crickets, grasshoppers, katydids, and weta) make a "chirping" sound come twilight, and Madagascar hissing cockroaches (Gromphadorhina portentosa) creates a hissing sound which it's named after. Cicadas vibrate their bodies to emit a rather ear-piercing racket in which, some books say, can even break the human ear drum! While the insect world is alive with sounds, has anyone ever thought about whether or not insects can hear?

While I was searching for material through various entomology journals, I came across an interesting article  done in 1986 which tested whether or not praying mantis (Order Mantodea) can hear. Written by David D. Yager and Ronald R. Hoy, it looked at the (currently non-existing) Order Dictyoptera, which included mantises, cockroaches, and termites (Since then, this Order has been split up into Mantodea and two suborders of Blattodea--roaches and termites). There are other insect groups which have been reported to have hearing capacity, including the Orthoptera mentioned earlier. Moths (Order: Lepidoptera) can also hear, due to a tympanal organ located on their thorax.

Anyway, the study did some research on a praying mantis species, Mantis religiosa, the European Mantis, and found that there is a tympanal organ located in the ventral midline. As said in the paper, mantises are, indeed, an "auditory cyclops."

Picture 1: Between the second set of legs
 (the metathoracic legs) is the location of the cycloptic ear on a
 praying mantis.

The study used seven males and six females for their research. Researchers used a wide variety of stimulation over a broad range of frequencies to see how the M. religiosa would react. Essentially, mantises can hear the best in the ultrasonic range: 25 to 45 kHz. To compare, I found on Wikipedia.com that humans can only hear 20 Hz to 20 kHz; that is still less than what the M. religiosa can pick up! This "ear" is structurally similar to what one would find on many moth species, lacewings (Order: Neuroptera), and part of a cricket's auditory system. Unfortunately, the tympanal organ does not help with where a sound comes from, just that it exists.

Through some experiments with the mantises, it was found that by covering the ventral area of the insect with melted wax, specifically over a deep, narrow groove found in the midline (between the metathoracic legs), it lost the ability to hear. This midline structure was, therefore, proven as a key part in the tympanal organ's success.

Another really interesting thing about this study was by disecting the mantis "ear", scientists found that it was made up of two tympana that were facing each other. separated by less than 150 micrometers. Since the organs face each other, and are located rather close to one another, this provides an explanation as to why mantises couldn't perceive direction with sounds during the tests.

Picture 2: Do praying mantises "pray"?

So, what's the point of this? Why has a mantis developed a single "ear"? Well, scientists aren't entirely sure (at the point of this study--remember, 1986!), but they did think of something interesting. Since some mantis species fly around looking for mates at night, their hearing can be used as a warning system. Moths, lacewings, and crickets use their hearing as a way of detecting a bat's sonar while flying. Preliminary research has shown that an Asian species of mantis from the Hymenopodidae family will dramatically change its flight pattern upon detecting bat-like ultrasound pulses. Cool, eh?

Well, I never really thought about insect hearing capacity until this point. That clearly does make sense, doesn't it?! What do you guys think?

~Mel







You can find the study at:
http://www.mantislab.com/380.pdf (scroll down a bit--it's towards the middle)

Picture 1:
http://farm4.static.flickr.com/3034/2558924463_aee9d72e23.jpg

Picture 2:
http://farm1.static.flickr.com/132/346799957_3705f17781.jpg