Katydids, belonging to the insect family Tettigoniidae, are known across the world as bush crickets or long-horned grasshoppers. These insects produce a loud, recognizable sound that dominates the summer and autumn soundscape. Although they are masters of camouflage, their distinctive calls make them far easier to hear than to see. Katydids use these species-specific sound signals for long-distance communication.
Describing the Signature Sound
The most common katydid sound is a sharp, rhythmic, and often raspy pulse that is easily mistaken for a bird or a frog. This characteristic sound is a rapid series of pulses or clicks, not a continuous tone. The sound is often high-pitched, though the fundamental frequency varies widely, ranging from the low audio spectrum up to extreme ultrasonic frequencies over 100 kHz.
The insect’s familiar common name comes from the specific song of one North American species, the Common True Katydid (Pterophylla camellifolia). This species produces a loud, three-pulsed song that listeners interpreted as mimicking the phrase “Ka-ty-did.” Variations of this call are sometimes heard as “Katy-didn’t,” or a simpler “Ka-ty.” The perceived quality of the sound is described as percussive and dense rather than a clear musical pitch, due to the presence of many complex overtones.
The Mechanics of Stridulation
Sound production in katydids is achieved through stridulation, a specialized process involving rubbing two modified body parts together. Katydids perform this action using structures located on their forewings, or tegmina, which are held over their backs. The mechanism is asymmetrical, utilizing a file on one wing and a scraper on the other, typically performed by the male.
The anal margin of the left forewing bears a serrated vein known as the stridulatory file, which is a row of tiny teeth. The right forewing possesses a sharp-edged structure called the scraper. Sound is generated when the katydid rapidly sweeps the scraper across the file’s ridges, creating a series of impacts that produce vibrations. These vibrations are immediately amplified by a specialized, drum-like membrane on the right forewing known as the mirror. The size and structure of the file, scraper, and mirror determine the specific frequency and intensity of the call. The entire wing acts as a resonator to project the loud signal.
Communication and Purpose
The primary function of the katydid’s song is sexual communication, serving as a long-distance mating call. The characteristic song is predominantly produced by the male to attract a female to his location. This acoustic signal is species-specific, ensuring the male attracts a female of the correct species.
In many species, the female responds to the male’s calling song with a shorter, often quieter signal. This duet helps the male pinpoint the female’s location for mating. Beyond courtship, katydid calls can also serve other functions, such as communicating territorial boundaries to ward off rival males. Some species may also produce protest or disturbance sounds when they are handled or feel threatened.
Timing and Hearing
The loud chorus of katydids is most often heard during the warm nights of summer and early autumn, as most species are nocturnal singers. Their calls dominate the nighttime soundscape, which is a distinct contrast to the sounds of cicadas, which primarily call during the day. This nocturnal habit means the insects are rarely seen, as they remain hidden high in trees and dense foliage.
The tempo of the katydid’s song is directly related to the ambient temperature, since their metabolism is affected by the environment. On warmer nights, the chirps are faster and higher in pitch, while cooler temperatures cause the tempo to slow down significantly. The directional nature of the sound, coupled with the insect’s camouflage, is essential for the insects to locate each other.