When Trees Scream

Scientists at Israel’s Tel Aviv University discovered that plants can “scream” ultrasonic sounds when they are in distress, such as when they experience a drought. 

These sounds are out of the range of the human ear, but researchers had believed that they could be heard by other insects or animals. 

They were right: In their new paper, the same team found that female moths can hear the plants’ sounds of distress, which influence their decisions whether to lay eggs on them. 

“This is the first demonstration ever of an animal responding to sounds produced by a plant,” Yossi Yovel, a neuroecologist and co-author of the study, told the BBC. 

For their experiments, Yovel and his colleagues turned to female moths, which lay their eggs on tomato plants to provide a food source for their larvae. 

“We assumed the females seek an optimal site to lay their eggs, a healthy plant that can properly nourish the larvae,” explained co-author Lilach Hadany in a statement. 

In the first test, the moths had to choose between a box with a speaker playing high-frequency distress sounds from dehydrated tomato plants, and another that was silent. Both boxes had no plants. 

The moths flew to the “noisy” box, with scientists suggesting that the choice was based on the fact that there was a living plant nearby – even though it was under stress.  

“In the absence of an actual plant, the moths indeed preferred to lay their eggs in proximity to acoustic signals which represent dehydrating plants,” they wrote. 

When researchers disabled their hearing organs, the insects showed no preference. This confirms that they were hearing and responding to plant-emitted sounds in the earlier experiment. 

Things got interesting in the second experiment, when the insects had to choose between two healthy tomato plants, one of which had a speaker playing the stress sounds of a dehydrated plant. 

Unsurprisingly, the moths flew toward the silent plant, suggesting they were picking the healthier choice.  

But in the third experiment, the females had to choose between a silent box and another that had male moths emitting ultrasonic signals similar to the plants. The females again weren’t picky about where they laid their eggs. The findings further showed that their behavior is specifically triggered by plant distress sounds, not just any ultrasonic signal. 

The study raises intriguing questions about whether other animals also eavesdrop on botanical distress calls and whether plants, in turn, respond to each other.  

The authors insist, however, that plants are not sentient: They noted that the distress sounds are generated through physical effects caused by changing local conditions. 

Even so, the study hints that plants and animals evolved together the ability to produce and listen to the sounds for their mutual benefit. 

“This is a vast, unexplored field,” Hadany told the BBC, an entire world waiting to be discovered.”