The chorus of chirps, buzzes, and trills heard on warm summer nights is often created by the katydid, an insect belonging to the Tettigoniidae family, commonly referred to as long-horned grasshoppers or bush crickets. These sounds are acoustic communication signals integral to the insect’s survival and reproduction. The specific patterns of the katydid’s song allow them to communicate with others of their species, facilitating everything from finding a mate to avoiding predators.
The Mechanism of Sound Production
Katydids produce their characteristic sound through a process called stridulation, which involves rubbing two specialized body parts together. In males, the sound apparatus is located on the modified forewings, known as the tegmina. The mechanism consists of a file and a scraper, which are positioned on the base of the wings.
The file is a row of microscopic teeth, or ridges, situated on a vein of one wing, while the scraper is a sharpened edge on the opposing wing. To generate a sound pulse, the insect rapidly opens and closes its forewings, drawing the scraper across the file. This friction causes the wing membrane to vibrate and resonate, amplifying the sound into the air.
The resulting sound is highly dependent on the physical structure of the apparatus. The movement is often asymmetrical, with the right forewing acting as the primary resonator for the sustained sound pulse. Some katydids also produce low-frequency substrate vibrations through their body and legs, which females can detect at close range on a plant or the ground.
The Primary Purpose: Courtship and Mating Calls
The most frequent and loudest sounds made by katydids serve the primary function of sexual signaling and pair formation. The male’s song is an advertisement call, a long-distance beacon designed to attract a receptive female. This call is costly to produce, requiring significant metabolic energy, and it also carries the risk of attracting predators.
Each katydid species possesses a unique calling song defined by specific parameters like frequency, duration, and repetition rate. This species-specific acoustic signature prevents interbreeding, ensuring that only females of the same species recognize and respond to the male’s call. Females often have a narrow range of preferred pulse rates and temporal patterns, using these details to locate a suitable mate.
The female, typically silent, will often produce a short, subtle acoustic response, such as a brief chirp or “tick,” once she is in close proximity to the male. This female response is a localized signal that guides the male to her exact location, completing the final stage of the rendezvous. The acoustic communication system is thus a two-way exchange, with the male initiating the long-distance call and the female providing the final, pinpointing signal.
Acoustic call features are also heavily influenced by the ambient temperature because katydids are cold-blooded. As the air temperature rises, the insect’s muscle activity increases, causing them to rub their wings faster. This physical change results in a higher chirp rate and a shorter interval between calls.
Beyond Reproduction: Territoriality and Defense Signals
While mating is the main driver for sound production, katydid noise also fulfills several other communication and survival needs. Rival males use distinct territorial calls to maintain distance or challenge competitors. These aggressive signals establish dominance and regulate the spatial distribution of singing males, which helps reduce competition for mates.
The insects also employ alarm or distress signals when they are physically captured or threatened by a predator. These sounds are short, harsh bursts designed to startle a potential attacker or warn nearby conspecifics. In some species, these defensive calls are produced by both males and females.