Read: Trees have their own songs

The concept of floral communication has long been controversial, especially after decades of pseudoscientific (but very popular) claims about plants growing well to classical music or being attuned to human emotions. Those hokey claims “have never been substantiated by rigorous experiments,” says Richard Karban from the University of California at Davis, and they tainted the entire field of study, making scientists skeptical about the very notion of plants exchanging signals.

But after many careful studies, it’s clear that plants can send airborne, chemical messages, warning faraway relatives about marauding plant-eaters, and that animals can eavesdrop on these communiqués. Plants can also influence one another through the network of fungi that connects their roots—a so-called wood-wide web. And they can respond to vibrations moving through their tissues: Many release pollen only when insects land on them and buzz at the right frequency, while others create defensive chemicals when they sense the rumbles of chewing insects.

To Hadany, one of the Tel Aviv University researchers, it seemed weird to think that plants wouldn’t also make use of sounds—airborne vibrations. “Plants have plenty of interactions with animals, and animals both make and hear noises,” she says. “It would be maladaptive for plants to not use sound for communication. We tried to make clear predictions to test that and were quite surprised when it worked out.”

First, two team members, Marine Veits and Itzhak Khait, checked whether beach evening primroses could hear. In both lab experiments and outdoor trials, they found that the plants would react to recordings of a bee’s wingbeats by increasing the concentration of sugar in their nectar by about 20 percent. They did so in response only to the wingbeats and low frequency, pollinator-like sounds, not to those of higher pitch. And they reacted very quickly, sweetening their nectar in less than three minutes. That’s probably fast enough to affect a visiting bee, but even if that insect flies away too quickly, the plant is ready to better entice the next visitor. After all, the presence of one pollinator almost always means that there are more around.

“This shows yet again that plants can behave in remarkably animal-like ways,” says Heidi Appel from the University of Toledo, who has studied plants’ responses to animal vibrations. Crucially, she says, the study is “ecologically relevant”—that is, it involves a sound (bee buzzes) and a response (nectar sweetening) that actually matter to the plant. It’s a far cry from past studies that showed plants reacting to sounds they would never normally encounter, such as classical music, in ways that are hard to interpret (certain genes might switch on or off, but to what end?).