Thursday, July 23, 2009

Cricket ears are amazing

A department store recently used this fact -- Crickets have ears on their knees! -- to peak interest in an email ad. I thought the claim sounded bogus (can you just picture a little cricket with tiny ears sticking out of its legs?), so I took to the Internet to investigate.

It turns out the ad is correct (my apologies to Kohl's). The University of Arizona Center for Insect Science Education Outreach states in their Cricket Information sheet that when the male chirps, "the resulting chirping sound is picked up by the female's ears on her front legs."

Still, I figured that these "ears" would be simple structures, nothing that would even come close to rivaling the complexity of the human ear. But again, I was mistaken. The book Artificial Neural Networks: Biological Inspirations – ICANN 2005 includes a paper entitled "New Ears for a Robot Cricket". The authors, Torben-Nielsen, Webb & Reeve, state that a cricket has "at least four body openings" used in hearing and describes the cricket's auditory system in this way:
[It] consists of two ear drums ... located on the forelegs and connected through a system of tracheal tubes. One extra sound opening on each side of the cricket body ... is also connected to the tracheal tubes.
In short, the cricket's auditory system is nothing less than amazing. The female cricket uses all of this auditory information to track down the location of the chirping male to mate with him.

Male crickets have an equally complex system for "singing", the noise they generate when rubbing their wings together. As scientist Axel Michelsen explains in the fascinating paper "The Tuned Cricket" (News Physiol Sci 13: 32-38, 1998), "a scraper on one wing hits a series of cuticular teeth on the other". (That's the male cricket's instrument!) The male cricket's wing then acts as a "loudspeaker" to amplify the sound so that the female can hear it. The song is optimized to account for the fact that crickets are low to the ground and the resulting frequency of the vibration ensures that the noise can be picked up and heard by the female.

According to Professor L. C. Miall in House, Garden and Field: A Collection of Short Nature Studies, both male and female crickets can hear:
The male cricket hears the sound which he produces, and the female hears the call of the male.
But only male crickets can sing, a fact I learned from the Minnesota Pollution Control Agency. They have a nice page about crickets that includes a coloring sheet, the formula for predicting the temperature based upon the number of cricket chirps in a given amount of time, and a recipe for (eeew!) chocolate-covered crickets.

If bugs are your thing, be sure you drop by The Center for Insect Science Education Outreach. Their website has advice for Using Live Insects in Elementary Classrooms for Early Lessons in Life, with lesson plans, information sheets about various insects (including crickets), and tips for caring and raising the little critters.

Photo credit: Larry Page, through a Creative Commons Attribution 2.0 Generic license.


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