Katydids have their ears near their knees

 

Up close with a Greater Anglewing katydid (Microcentrum rhombifolium). Katydids "sing" with their wings, rubbing the bases together in a process known as stridulation. One wing contains a file, the other a scraper. In the case of the Greater Anglewing, males create a series of soft clicks, as if two pebbles are being tapped together. It stands to reason that these insects would have good hearing, as males create the songs to attract females or maintain unique territories. Indeed, they do hear well, courtesy of ears on their forelegs, just below the knee. It's that elongate vertical slit on the katydid's foreleg in the photo.

Katydids and their orthopteran allies represent the genesis of intentional sound. Fossil records of katydid relatives date back 250 million years ago, replete with the file/scraper sound system. Although life on earth began over 3.5 billion years ago, the earliest animals were mute. Animal sound didn't originate until the katydids came along, and over the eons the faunal soundscape has evolved into a gorgeous, complex aural tapestry that involves legions of different animals making their own types of music.

Alas, the orthopteran symphony will soon cease at northerly latitudes, like where I live in central Ohio. But they're still going strong, and we've probably got another two weeks or so to enjoy their ancient melodies.

A greater Anglewing poses on the foliage of Winged Sumac (Rhus copallinum). The large katydid is a remarkable leaf mimic.