We tend to think of plants as static and unchanging. Whatever happens to them, they just take it. But that’s not nearly the case. Not only do plants have ways of picking up cues from their surrounding environment, but they react and adapt to them.

Case in point: when plants “hear” pollinators around, they increase their sugar and nectar volume, and even change their gene expression.

Pollinators? Right this way

When pollinators choose flowers they use more than just their sight. They use their full array of senses, and we’ve mostly ignored vibrations until now.

“Plant-pollinator coevolution has been studied primarily by assessing the production and perception of visual and olfactory cues, even though there is growing evidence that both insects and plants can sense and produce, or transmit, vibroacoustic signals,” says Francesca Barbero, a professor of zoology at the University of Turin. Barbereo and her collaborators (an interdisciplinary mix of entomologists, sound engineers, and plant physiologists) studied these signals to develop noninvasive and efficient methods to monitor pollinator communities.

Recently, they set out to test a simple but provocative idea: can plants actually hear their pollinators?

Plants, obviously, have no ears — no nervous system, either. But they do have various specialized mechanoreceptors. These receptors specialize in external stimuli such as vibrations, even the vibrations produced by a bee’s wingbeats or buzzing. This vibration-sensing ability would, in theory, give the plants the chance to respond to specific pollinators in real time

They chose the common snapdragon (Antirrhinum majus) as their test subject and played recordings of buzzing bees near the flowers using delicate sound equipment. Specifically, they used the sounds of Rhodanthidium sticticum, a bee species well-matched to snapdragons’ floral structure and known to be an effective pollinator.

It worked. The plant sweetened its nectar, made more of it, and rewired its own gene expression.

Plants react

The response wasn’t generic. When the team played recordings of other insects (such as non-pollinating wasps) or ambient background sounds, the flowers didn’t react the same way.

That strategy may be evolutionary in nature. A plant that can detect the buzz of a trustworthy pollinator might use that cue to serve up a sweeter reward, enticing the insect to linger longer, increasing the chances of successful pollination.

“The ability to discriminate approaching pollinators based on their distinctive vibroacoustic signals could be an adaptive strategy for plants,” said Barbero. “By replying to their proper vibroacoustic signal — for instance, an efficient pollinator’s — plants could improve their reproductive success if their responses drive modifications in pollinator behavior.”

However, it’s not clear if this strategy actually works. It’s also unclear whether all or some plants do it.

The team is now exploring this and other questions. Can plant-generated sounds influence insect behavior? Could certain sounds repel nectar robbers — species that take nectar without offering pollination in return? And what happens when a flower is exposed to the buzzing of different pollinators?

Potential for plant “hearing”

This surprising plant behavior, unveiled this week at the 188th Meeting of the Acoustical Society of America in New Orleans, adds to the growing body of evidence that plants are not the passive green fixtures we often imagine. Instead, they are alert, responsive, and astonishingly attuned to the world around them — including, it seems, the sound of their pollinators.

There could even be a potential practical application to this.

“If this response from insects is confirmed, sounds could be used to treat economically relevant plants and crops, and increase their pollinators’ attraction,” said Barbero.

The findings have not yet been published in a peer-reviewed journal.