Venus Fly Trap’s Mystery Revealed

A Harvard professor with a passion for studying everyday phenomena, including how worms wriggle, flags flap, and skin shrivels, has co-authored a report research explaining how the Venus flytrap is able to snap shut almost instantaneously.

Gordon McKay Professor of Applied Mathematics and Mechanics Lakshminarayanan Mahadevan’s research was published in the Jan. 27 issue of the scientific journal Nature.

Yoël Forterre of the Université de Provence, Jan M. Skotheim of the University of Cambridge, and Harvard’s Assistant Professor in the Department of Organismic and Evolutionary Biology Jacques Dumais were co-authors.

Mahadevan explained in an interview that when an insect lands on one of the flytrap’s hinged leaves, it stimulates small hairs on their surfaces. This stimulation moves water within the plant and causes the flytrap to store elastic energy, which is then released as the flytrap shuts. Once the plant snaps shut, it takes hours to reopen.

“When the water moves, it changes the curvature in the leaf in one direction that causes it to flip like a tennis ball or a contact lens,” said Mahadevan, whose first Venus flytrap came in 2002 as a gift from Dumais, who was then a post-doctoral student in Mahadevan’s lab.

“I had been thinking about [the flytrap’s movement] on and off. Then we had it in front of us,” Mahadevan remembers.

“Mahadevan has a way of looking at the world that is just really unique. He’s written a beautiful story about a fascinating event of a plant,” said Howard A. Stone, Joseph professor of engineering and applied mathematics.

To study the flytrap’s movement, Mahadevan used a high speed ultraviolet video, and then developed a mathematical model to describe the movements. Instead of insects, he used a glass rod to stimulate the flytrap’s leaves.

Mahadevan had to stimulate the same hair twice within a 10-15 second time frame in order to get the plant to shut.

This precautionary measure helps the plant prevent a “false alarm,” an unnecessary closing due to a touch such as that of a falling leaf, rather than an insect, he explained.

Mahadevan’s research interests center on things that are familiar, but that are often not understood completely. Some of his past research includes the study of how flies stick and unstick themselves to walls.

Everyday phenomena interest Mahadevan because, he said, “You don’t have to go to a fancy lab. You can look at how honey coils or folds when it hits your toast...how paper crumples or skin wrinkles.”

He credits his Ph.D. advisor, Joseph B. Keller, professor of mathematics and mechanical engineering emeritus at Stanford, for teaching him that one can think of anything and see something interesting in it.

As for the future, Mahadevan says he has a lot of “little plans.”

“I’d like to start thinking about biology and we have started thinking about how fish swim, how cells might move in particular ways, how speech works—how we are able to form consonants by driving air through the vocal folds and out of the mouth,” he said. “If there was a theme, the theme is really trying to look at robust phenomena in our daily world.”