Over a span of five years, Jayne Yack, a biology professor at Carleton, and a team of researchers discovered various species of caterpillars make distinct sounds to defend themselves against predators.
During trips to Costa Rica and Ecuador, Yack and her team found four distinct sounds that the caterpillars can make: whistling, chirping, clicking, and vocalizing. The sounds are audible only as vibrations, not as sounds in the air.
“We’re starting to look into how effective the sounds are,” Yack said. “The sounds are very effective, especially the whistling sound . . . some of these sounds freak birds out.”
According to Yack, whistling occurs through the caterpillar’s air holes, while chirping happens when the caterpillar grinds their mandibles together. Clicking, on the other hand, is when the caterpillar ‘clicks’ their mandibles together, creating a ticking sound. Vocalizing happens when caterpillars build up air in their gut and then release it through their mouth.
Yack said she thinks the whistling and vocalizing sounds, which are long in duration and loud, are used to startle the predator.
“It’s probably used to make the predator freak out and hop away and not be bothered by it,” Yack said.
The chirping and clicking sounds are short ticking noises that are often followed by regurgitation or some kind of chemical defence.
“Those sounds are more teaching the predator of what is yet to come,” she said.
To measure the sounds, Yack and her team used a range of microphones that can detect sound frequencies below and above what humans can hear.
“We don’t hurt them, we just give them a little pinch behind their head and that would simulate to some extent the peck of a bird,” she said. “We then videotape them and record with various microphones to see what types of sounds they make.”
The caterpillars that were studied come from a group called Bombycoidea, a species that become moths and are found around the world. Each species examined produced only one type of sound, Yack said.
Although the findings are significant in understanding caterpillar defence, Yack said that she believes that this is just the beginning.
“This is just the tip of the iceberg, as we are just starting to document all these sounds. We’ll probably find more sounds, we’ll probably find all kinds of things,” she said.
“We really just need to start looking at why certain species are making certain sounds. What is it attributed to their evolution history, and what is attributed to the function?” Yack said. “It’s probably a whole new world that we’re just starting to really uncover.”
