Not So Silent After All: Caterpillars Actually Whistle Like Tea Kettles

Flying insect numbers drop, threatening world ecosystem
If you thought that caterpillars don’t make sounds, then you couldn't have been more wrong. The insects actually use the same mechanism as a whistling kettle to cry when attacked by predators.  ( Greg Dwyer | Wikimedia Commons )

Who would have thought that certain types of caterpillars could actually produce clicking and hissing sounds when attacked?

These slow-moving insects are known to make noise only when snacking on leaves, but besides that, they are among the most silent in the animal kingdom.

A new study has proven otherwise, however, as a Nessus Sphinx Hawkmoth caterpillar was recorded crying faintly and creating strange sounds that seemed like a combination of spitting and static noise.

At first, scientists were stumped at how the insect is able to make such sounds considering its limited anatomy, but they found out later on that it actually uses the same mechanism a tea kettle does when it begins whistling.

Obtaining Recordings Of Attacked Caterpillars Crying

To obtain sound recordings, a research team from Carleton University in Ottawa, Canada, captured female moths of the species and then waited for their eggs to hatch in the laboratory.

As soon as they emerged into caterpillars, scientists then surrounded the insects with specialized microphones and gently "attacked" them using a pair of forceps.

To imitate a predator's attack, the caterpillars were slightly pinched just right behind their heads triggering them to open their mouths and emit a loud noise. This could only mean that the sound did not come from the critter's mandibles but from inside its body.

At that point, scientists were left with one big dilemma: how would it be possible for them to look into the insect's body to determine which structure allows them to make noise?

"Right now, we don't have the equipment to do that kind of thing," said Jayne Yack, a biology professor at Carleton University and co-researcher of the study.

Determining The Structure Allowing Caterpillar Sound Production

As an alternative, one of the scientists and Carleton University biologist Melanie Scallion opened up the insect's throats to look for the particular structure responsible for sound production. Unfortunately, she came up with no relevant findings.

Another co-researcher thought of taking a different course. Craig Merrett, an assistant professor at Clarkson University's Department of Mechanical and Aeronautical Engineering in New York, decided to build models after analyzing the caterpillar's sound waves.

Through his models, he identified the possible mechanism utilized by the insect when it "cries" during an attack. It makes the unusual sound by forcing air through a constricted structure found between its foregut chambers. Basically, it works like a whistling kettle forcing air through its spout.

The sound only becomes louder as the esophagus amplifies certain frequencies when air passes through the constricted structure, producing the same noise made by a person blowing across a bottle's mouth.

Results have been published Feb. 26 in the Journal of Experimental Biology.

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