Scientists demonstrate for the first time that plants and animals interact using sound

Female moths don’t rely on sight or smell alone. They can also hear stressed plants. Scientists found that these insects detect ultrasonic clicks from plants under drought stress and use them when choosing egg-laying sites.

Plants emit airborne ultrasonic sounds when stressed. These vibrations, previously thought to be undetectable by animals, can travel through the air. The Egyptian cotton leafworm moth, Spodoptera littoralis, hears these sounds.

This species has tympanic ears sensitive to the 20 to 60 kHz range, with peak sensitivity around 38 kHz. That is where many plant clicks fall.

The researchers hypothesized that female moths might use these plant sounds to decide where to lay eggs. Their experiments confirmed this.

Understanding plant communication

Plants may not have mouths or ears, but they definitely talk – and listen. Through their roots, leaves, and even the air, they exchange chemical signals to warn each other of danger, call for help, or share resources.

When a caterpillar chomps on a leaf, for example, some plants release volatile compounds that drift to their neighbors, triggering defensive measures like bitter-tasting chemicals or toughened leaves.

Underground, fungi form vast mycorrhizal networks – often called the “Wood Wide Web” – that help trees and plants share nutrients, send distress signals, and maintain the balance of the ecosystem.

What’s wild is how intentional it all seems. Certain plants send out distress chemicals only when their kin are nearby, suggesting a level of familial recognition.

Others can distinguish between friend and foe based on the scent of another plant’s emissions. It’s not just survival – it’s community.

Moths respond to plant sounds

The study involved multiple experiments with precise setups. In a no-plant environment, moths preferred laying eggs near a speaker playing recorded plant stress sounds.

When these moths were deafened, the preference disappeared. This proved that the response came from hearing, not other cues.

In contrast, when healthy plants were added and the same sounds were played near one, the moths chose the silent plant. This indicated that when real plants were present, moths correctly interpreted the sounds as warnings.

“After proving in the previous study that plants produce sounds, we hypothesized that animals capable of hearing these high-frequency sounds may respond to them and make decisions accordingly,” said study co-author Professor Yossi Yovel from Tel Aviv University.

“Specifically, we know that many insects, which have diverse interactions with the plant world, can perceive plant sounds. We wanted to investigate whether such insects actually detect and respond to these sounds.”

Do plant sounds change moth behavior?

In longer arenas, moths laid more eggs near either the sugar feeder in the center or the sound-emitting speaker at one end. They laid none near the silent resistor at the other end.

These results were consistent across different click rates and setups. When tracked, moths spent more time on the side with plant sounds before deciding.

Even though the courtship sounds of male moths fell in a similar frequency range, females showed no egg-laying preference for the male side. This confirmed that the response was specific to plant sounds.

“We chose to focus on female moths, which typically lay their eggs on plants so that the larvae can feed on them once hatched. We assumed the females seek an optimal site to lay their eggs – a healthy plant that can properly nourish the larvae,” said co-author Professor Lilach Hadany.

“Thus, when the plant signals that it is dehydrated and under stress, would the moths heed the warning and avoid laying eggs on it? To explore this question, we conducted several experiments.”

Integrating sound and smell

Without a visible plant, sound becomes the only cue. So moths associate it with plant presence. But when they can see or smell real plants, and one gives off stress sounds, they avoid it. This shows a context-based decision-making process.

The researchers also tested moth antennae. Using electroantennogram recordings, they found strong differences in odor detection between drying and hydrated plants. This shows that moths integrate sound and smell.

In real tomato plant patches, the click rate reaches about 20 per minute. In experiments, sounds were played at 30 to 60 clicks per minute.

This simulated what a moth might hear near many stressed plants. Sound levels used matched those measured in live plants.

Acoustic interactions in nature

This study reveals that plant sounds can guide insect behavior. Moths may not just rely on smell or touch. Instead, they interpret ultrasonic cues. The researchers think other animals, perhaps pollinators or predators, might also use these sounds.

While the plant clicks likely evolved as a by-product of water loss, they now serve as useful cues. Scientists predict more discoveries in this area.

“In this study, we revealed the first evidence for acoustic interaction between a plant and an insect. We are convinced, however, that this is just the beginning,” noted the researchers.

“Acoustic interaction between plants and animals doubtlessly has many more forms and a wide range of roles. This is a vast, unexplored field – an entire world waiting to be discovered.”

The study is published in the journal eLife.

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