(R. E. Snodgrass) A female cricket. The red ring indicates the ear position on her left leg. Drawing courtesy of R. E. Snodgrass, modified by author.
What Animal Hears with Its Legs, and Why?
APRIL 08, 2010April Holladay, HappyNews ColumnistQ: Name a creature which uses its legs to hear.
Alexud, Pensacola, Florida, USA
A: Crickets have ears on their front legs, located about where humans have elbows. Katydids also have leg ears.
In fact, ears "(tympanal organs) lie beneath a drum-like membrane (the tympanum) where they respond to sound," says entomologist John Meyer, professor at North Carolina State University. These 'ears' may be located on the thorax (in some true bugs), on the abdomen (in grasshoppers, cicadas, and some moths), or on the front tibia (in crickets and katydids)."
A calling male cricket creates a racket — chirping loudly at a fixed frequency that depends on his species and the night temperature. A female hears the beckoning calls, determines the direction of the chirp source and tracks down the male chirper, "purely based on auditory cues," says zoologist Martin Lankheet of Wageningen University. She distinguishes direction by listening to the time difference she hears from her right and left ears.
The two ears consist of eardrums (small, pale spots) spaced about 12 millimeters (0.5 in) apart on her left and right legs. She hears a sound coming from right of her position, for example, with her right ear before she hears it with the left. The time delay tells the direction of the chirping male.
Perhaps crickets developed ears on their legs to increase the separation distance between their ears. Indeed:
"Because crickets are very small compared to the wavelength of male sounds, an increase in the separation distance increases the difference in signals between the two ears. Moving the ears further apart therefore helps direction discrimination, and mate finding," emails Lankheet.
Frogs' Hearing, WonderQuest
A closer look at cricket hearing, email from Martin Lankheet.
Cricket directional hearing by Martin Lankheet, Wageningen University, The Netherlands
Mechanorecptors by John R. Meyer, North Carolina State UniversityApril Holladay lives in Albuquerque, New Mexico. Her column, WonderQuest, appears every second Monday of the month on WonderQuest.com. To read April's past columns, please visit her website. If you have a question for April, visit this information page.
(Answered 12 April 2010)