Plants can "hear" a caterpillar's munching sound and arm themselves with more chemicals to prepare for predators, a new study has found.

Two University of Missouri scientists conducted research using two groups of plants: a control group kept in silence and a group that was exposed to a recording of caterpillars eating leaves, the New York Times reported.

The set of plants exposed to sounds of munching caterpillars produced more chemicals to repel the predators once they began eating the plants. Study author Reginald B. Cocroft, a behavioral ecologist, noted that the plants responded to extremely small vibrations from the caterpillar sounds.

"There were feeding vibrations that got a strong response from plants that vibrated the leaf up and down by less than one ten-thousandth of an inch," said Cocroft, as quoted by the Times.

Plants exposed to the sound of wind and other insects didn't produce more caterpillar-repelling chemicals, causing the researchers to theorize that plants can tell the difference between predators and other noises. The plants that heard caterpillar chewing prior to being exposed to the insects quickly fortified themselves against the oncoming predators.  

"So when the attack finally happens, it's kaboom," said Heidi Appel, a chemical ecologist and another study author, as quoted by the Times. The anti-caterpillar chemical comes "faster and often in greater amounts."

Prior studies have revealed that plants respond to other sounds; for example, research has shown that rice has two genes that turn on if the plants are exposed to music or clear tones.

For this particular study, scientists wanted to see how plants practically used their sensitivity to sound vibrations to protect themselves.

Plants "don't normally experience music or pure tones in their environment," Cocroft pointed out. "We wanted to ask, 'Why would plants evolve this ability to hear sounds or vibrations?'"

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