The life of a caterpillar before it enters its cocoon mostly consists of eating as much as it can while avoiding being eaten itself. To stay alive, the Nessus sphinx hawkmoth caterpillar’s defense mechanism is a scream.
It sounds a little like this: ssss- kih-kih-kih.
Scientists recently discovered that this species of caterpillar shouts, which they explain is due to a “mechanism analogous to a whistling kettle” in a study released Monday in the Journal of Experimental Biology. It’s not exactly a voice, but the result of air being forced into and out of its gut. The researchers write:
“We propose that sound is generated by ring vortices created as air flows through the orifice [the mouth] between two foregut chambers (crop and esophagus) … As air flows past the orifice, certain sound frequencies are amplified by a Helmholtz resonator effect of the esophagus chamber. Long sound units occur during inflation, while short sounds units occur during deflation.”
The effect creates the scratchy-hiss displayed below:
The hissing part you hear at the start of the video is thought to be because of the first inhale of air, and then the scratch sound that starts at six seconds is the release of air.
While this in-and-out process is described as similar to a boiling tea kettle, the researchers also note the aeroacoustic mechanisms are “similar to rocket engines.”
The Nessus sphinx hawkmoth caterpillar is unique in how it uses air and its mouth to create noise, but it’s not the only caterpillar that’s capable of making a sound. Study co-author Jayne Yack, Ph.D., has discovered four other sound-producing mechanisms that caterpillars use to ward off predators and communicate with other caterpillars. The masked birch caterpillar, for example, use vibration signals to resolve territorial disputes over their homes. Other caterpillars release oxygen through pores and rub their mouths together to make noise.
Yack notes that “surprisingly little is known about how caterpillars use sounds and vibrations to communicate.” Understanding the vocalization of the Nessus sphinx moth caterpillar is a start — and an opportunity to appreciate our own expansive capacity to communicate.
To avoid becoming bird grub, other species of caterpillars employ a range of defense mechanisms, including camouflage, toxic chemicals, and bristly backs.