There may be some truth to the speaking abilities of the babbling caterpillar from Alice in Wonderland, but instead of speaking in prose, researchers have found the little insects can whistle like tea kettles.
The hawkmoth and sphinx moth caterpillars screech when they feel threatened by predators, but exactly how remains another question.
It seems an extraordinary feat considering the insects don’t inhale air through their mouth. Unlike most vertebrates, caterpillars don’t have lungs. They breath when air enters through spiracles on the outside of their bodies.
Researchers set up captive caterpillars with their very own recording studio. While poking and prodding the poor crawlies, researchers moved a microphone around the body to record where the sound was coming from.
“You just have to pretend that you are a bird pecking at the caterpillar, so you take blunt forceps and give them a quick pinch to the body,” said researcher Jayne Yack of Canada’s Carleton University in a statement.
At the very least, scientists figured the sounds were coming from the caterpillars' mouths. At first, scientists thought the caterpillars ground their mandibles together to make the spitter-spatter sound resembling a tea kettle, but soon checked that off the list.
“We videotaped the mouth parts using a macro lens and found that the mandibles (chewing parts) were held open during sound production,” said Yack.
This means the whistles had to come from inside the body.
Study co-author Melanie Scallion dissected the caterpillars’ throats to look for structures responsible for the sounds, but couldn’t find anything. What could have been a dead-end became an opportunity for discovery.
Craig Merrett, assistant professor in the Department of Mechanical and Aeronautical Engineering at Clarkson University, analyzed the sound waves produced by the caterpillars. He thinks the caterpillars force air through a constriction between the crop and esophagus (foregut chambers) to generate the whistling sound. As air passes through a constriction in the throat, certain frequencies are amplified in the esophagus. It works the same way sounds are made when you blow across the mouth of a glass bottle.
Essentially, by forcing air in and out of their guts, caterpillars create sound "in much the same way that jet engines generate their roar and kettles whistle." The sounds aren’t random, either. Researchers recorded sounds that were patterns of long and short whistles.
“This is really remarkable, considering that caterpillars are not considered to be ‘acoustic’ insects,” said Yack. Even so, other caterpillars have been found to make sounds, like this walnut sphinx moth larvae.
Scientists still are not sure how the caterpillars draw air into the top portion of their guts, but Yack says she hopes to use X-ray visualization to figure out how to observe the muscle movements within their throats.
They may not be blowing smoke rings, but these little bugs have mastered a similar concept as rocket engines to scare off unwanted predators.
The study was published in the Journal of Experimental Biology.