Highest whistle by a caterpillar

The noisiest caterpillar is that of the walnut sphinx Amorpha juglandis, a widely distributed species of North American hawk moth. If attacked by a predator such as a bird, the caterpillar of this species forcefully expels air from a pair of respiratory holes called "spiracles" on its eighth abdominal segment. This expulsion creates a loud, high-pitched whistling sound, attaining frequencies of up to 22 kHz, whose function is presumably to startle the predator and thence prevent the caterpillar from being eaten by it.

A session, or 'train', of whistling lasts from 44 to 2060 milliseconds, and consists of one to eight whistles. The whistles are of three types: broadband, pure whistles, and multi-harmonic plus broadband, with mean dominant frequencies at 15 kHz, 9 kHz and 22 kHz respectively.