For World Bee Day: Flowers Can Hear Buzzing Bees—And it Makes Their Nectar Sweeter

An evolutionary theorist has set out to prove that plants can hear their surroundings, and she was right; they can.

Her work, not yet peer-reviewed, but available in a preprint repository, looked at the flowers of the evening primrose and used sound tests to prove they responded to the sound of bees’ wings by increasing the sugar quantity in their nectar.

Reasoning that pollinators and flowers have co-evolved over a very, very long time, and that the world is completely saturated with sounds, Lilach Hadany, who teaches at the intersections between mathematics and biology at the University of Tel Aviv, felt it wouldn’t make any sense for plants to ignore them.

Any living creature must make use of all its senses to survive until it can reproduce, and if one takes a moment to imagine how long a deaf or blind wildebeest would last on the Serengeti, they can see where Hadany is coming from.

To test her premise—that sound is an abundant natural resource that greatly aids in the quest to survive and thrive, Hadany subjected the flowers of the evening primrose to five sound tests consisting of three different computer-generated frequencies, silence, and the recording of a honeybee’s wingbeats.

The sweet science

Silence, which they achieved by placing a jar over the flower, computer generated high-frequency notes at 158 to 160 kilohertz, and intermediate-frequency notes at 34 to 35 kilohertz, all had no effect on the flower—the study shows.

However with the ultra-low frequency and the bee wingbeats, the flower spent the following three minutes increasing the sugar content in its nectar by 17-20%, a remarkably clear suggestion that Hadany’s hypothesis was right.

A flower with more nectar is more likely to be detected and visited by pollinators, and Hadany’s team found that pollinators were nine times more likely to choose to visit a flower that had been visited by another pollinator within the last six minutes, showing how valuable that small increase in sugar could be for the flower’s chances of reproduction.

“We were quite surprised when we found out that it actually worked,” Hadany told National Geographic. “But after repeating it in other situations, in different seasons, and with plants grown both indoors and outdoors, we feel very confident in the result.”

As Hadany and her colleagues thought about the nature of sound and flowers, it hit them that a great many flowers are concave, tubular, or bowl shaped—all perfect forms for attracting sound and vibrations.

Amphitheaters, sub-woofers, ears, and radar dishes all share these properties.

In fact, using tools to measure minute vibrations, they discovered that vibrations entering into the primroses increased in strength as a function of the shape of the flower petals, which if distorted or removed, cancelled out the effect.

On a different note, another study found that when the sound of caterpillars eating leaves was played next to a plant from the same family as mustard, they were later found to have flooded their leaves with a chemical caterpillar deterrent compared to those that heard only silence.

These two papers have helped open up a relatively new field of study—phytoacoustics, the study of plants’ interactions with sound.

As this is World Bee Day, it’s important to likewise recognize the importance of their food source, especially when selecting which species to plant in your yard or balcony—perhaps those with radar dish-like flowers?