From evolutionist Charles Darwin onward, scientists have pondered how the Venus' flytrap can snap its leaves closed around an insect in less than a tenth of a second even though it has neither muscles nor nervous system.
Now, using a high-speed camera, a team of researchers has shown that the rapid movement is caused by structural tension similar to that which causes a contact lens to suddenly flip from concave to convex when it is handled.
The key to the action is the complex curvature of the leaves, which creates powerful tension, according to biologist and mechanical engineer Lakshminarayanan Mahadevan of Harvard University.
Mahadevan and his colleagues painted tiny fluorescent dots on the leaves of a flytrap and then filmed it under ultraviolet light. Using mirrors to record different angles, they were able to determine how the leaves' shape changed when an insect was captured.
The leaves' most stable configuration occurs when they are closed to form a chamber. The plant is able to open itself over about an eight-hour period, leaving it in a delicately balanced tension between open and closed.
How the plant opens is not well understood, but scientists believe it involves pumping water into specific cells.
When a fly or other insect lands on the leaves, it apparently triggers the release of fluid from those cells, allowing the leaves to snap back to their normal shape, the team reported this week in the journal Nature.
"I thought it would be fun," Mahadevan said of the project. "Besides, as a vegetarian, it's nice to think about plants that eat animals rather than the other way around."