Sound production in Lepidoptera is reported in adults and larvae through a variety of different mechanisms, depending on the species. A recent comparative analysis identified four distinct types of sound production mechanisms for caterpillars of the superfamily Bombycoidea, including whistles, chirps, clicks, and vocalizations. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an Original Essay Vocalization, such as squeaks and hisses, is an unusual and poorly documented form of sound production for insects. Vocalization has been defined as any sound produced as a byproduct of food or through the action of an animal's respiratory system (air flow). These sounds can be produced either through aerodynamic mechanisms or through a mechanically vibrating element. Until recently, caterpillar vocalization was not documented. Initially, sound production using airflow mechanisms was studied extensively and confirmed experimentally for only two insect species, the African moth (Acherontia atropos) and the Madagascar hissing cockroach (Gromphadorhina portentosa). Vocalization is now observed for several caterpillars of the Macroglossinae subfamily. For example, vocalization is reported for Sphecodina abbottii, Amphion floridensis, Pachygonidia drucei and Nyceryx magna. However, the proposed mechanisms for sound production for these species were based solely on the observation that the mandibles (chewing parts) were held in an open position during sound production and have not been verified experimentally. A recent study provided experimental evidence in support of vocalization in Nessus sphinx hawkmoth A. floridensis larvae. A. floridensis larvae force air in and out of the intestine when attacked by birds, making a hissing sound through the oral cavity. The sound is produced by ring-shaped vortices created as the larvae force air through the narrow opening between the crop and the esophagus (chambers of the foregut). Although recent studies have advanced the current understanding of vocalization in some lepidopteran larvae, further research is needed. Unlike vocalization, the whistle is generated by the flow of air through the abdominal spiracles (external respiratory opening of insects). The defensive whistle is observed only in caterpillars of the Smerinthinae subfamily. The North American walnut sphinx (Amorpha juglandis) produces trains of high-pitched whistles by expelling air through two enlarged spiracles on the eighth abdominal segment when attacked by avian predators. A similar mechanism is documented for the worm caterpillar (Langia gingerides). The defensive whistling observed in these two species is an example of convergent evolution, as Amorpha and Langia are not closely related. In larval moths, clicks and chirps are the most common form of sound production and are typically generated through stridulation (the act of producing sounds by rubbing or striking particular body structures). Chirps are generated by rubbing the serrated edge of one jaw against the smooth internal surface of the other, which typically produces a series of pulses. Short clicks are produced by snapping the front side of one mandible against the serrated inner surface of the opposite mandible, while other species have been shown to produce a series of clicks using serrated "teeth" on opposing mandibles. Very few species of the Sphingidae family are known to vocalize as adults as part of a defense strategy. Until recently, squeaking as a defense mechanism was documented.