What sound-producing organs do male katydids rub to sing?

Male katydids rub their forewings together to produce their songs.

The mechanism is a form of stridulation. One forewing bears a toothed file, while the other has a scraper. As the wings move against one another, the file and scraper generate vibrations that are amplified by the wing surfaces. In many species, males use these songs to attract females or communicate during courtship.

Katydid songs are often heard at night, when many species are active and background noise may be lower. Their calls can be species-specific, helping females locate appropriate mates. Some katydids produce ultrasonic components that humans cannot hear, while others have conspicuously loud audible songs.

The hind legs are primarily associated with jumping, which creates a common mix-up. Katydids are related to crickets and grasshoppers, but sound-making structures differ among species, so not every singing orthopteran uses exactly the same body arrangement.